Re: [Xen-devel] [PATCH v2] x86/paravirt: Don't make vcpu_is_preempted() a callee-save function
On 14/02/17 14:46, Waiman Long wrote: > On 02/14/2017 04:39 AM, Peter Zijlstra wrote: >> On Mon, Feb 13, 2017 at 05:34:01PM -0500, Waiman Long wrote: >>> It is the address of &steal_time that will exceed the 32-bit limit. >> That seems extremely unlikely. That would mean we have more than 4G >> worth of per-cpu variables declared in the kernel. > I have some doubt about if the compiler is able to properly use > RIP-relative addressing for this. Anyway, it seems like constraints > aren't allowed for asm() when not in the function context, at least for > the the compiler that I am using (4.8.5). So it is a moot point. You can work the issue of not having parameters in a plain asm() statement by using an asm-offset, stringizing it, and have C put the string fragments back together. "cmpb $0, " STR(STEAL_TIME_preempted) "(%rax);" ~Andrew ___ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel
Re: [Xen-devel] [PATCH v2] x86/paravirt: Don't make vcpu_is_preempted() a callee-save function
On Tue, Feb 14, 2017 at 09:46:17AM -0500, Waiman Long wrote:
> On 02/14/2017 04:39 AM, Peter Zijlstra wrote:
> > On Mon, Feb 13, 2017 at 05:34:01PM -0500, Waiman Long wrote:
> >> It is the address of &steal_time that will exceed the 32-bit limit.
> > That seems extremely unlikely. That would mean we have more than 4G
> > worth of per-cpu variables declared in the kernel.
>
> I have some doubt about if the compiler is able to properly use
> RIP-relative addressing for this.
Its not RIP relative, &steal_time lives in the .data..percpu section and
is absolute in that.
> Anyway, it seems like constraints
> aren't allowed for asm() when not in the function context, at least for
> the the compiler that I am using (4.8.5). So it is a moot point.
Well kvm_steal_time is (host/guest) ABI anyway, so the offset is fixed
and hard-coding it isn't a problem.
$ readelf -s defconfig-build/vmlinux | grep steal_time
100843: 00017ac064 OBJECT WEAK DEFAULT 35 steal_time
$ objdump -dr defconfig-build/vmlinux | awk '/[<][^>]*[>]:/ { o=0 }
/[<]__raw_callee_save___kvm_vcpu_is_preempted[>]:/ {o=1} { if (o) print $0 }'
810b4480 <__raw_callee_save___kvm_vcpu_is_preempted>:
810b4480: 55 push %rbp
810b4481: 48 89 e5mov%rsp,%rbp
810b4484: 48 8b 04 fd 00 94 46mov-0x7db96c00(,%rdi,8),%rax
810b448b: 82
810b4488: R_X86_64_32S __per_cpu_offset
810b448c: 80 b8 d0 7a 01 00 00cmpb $0x0,0x17ad0(%rax)
810b448e: R_X86_64_32S steal_time+0x10
810b4493: 0f 95 c0setne %al
810b4496: 5d pop%rbp
810b4497: c3 retq
And as you'll note, the displacement is correct and 'small'.
The below relies on the 'extra' cast in PVOP_CALL_ARG1() to extend the
argument to 64bit on the call side of things.
---
arch/x86/kernel/kvm.c | 21 +
1 file changed, 21 insertions(+)
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 099fcba..2c854b8 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -589,6 +589,7 @@ static void kvm_wait(u8 *ptr, u8 val)
local_irq_restore(flags);
}
+#ifdef CONFIG_X86_32
__visible bool __kvm_vcpu_is_preempted(int cpu)
{
struct kvm_steal_time *src = &per_cpu(steal_time, cpu);
@@ -597,6 +598,26 @@ __visible bool __kvm_vcpu_is_preempted(int cpu)
}
PV_CALLEE_SAVE_REGS_THUNK(__kvm_vcpu_is_preempted);
+#else
+
+extern bool __raw_callee_save___kvm_vcpu_is_preempted(int cpu);
+
+asm(
+".pushsection .text;"
+".global __raw_callee_save___kvm_vcpu_is_preempted;"
+".type __raw_callee_save___kvm_vcpu_is_preempted, @function;"
+"__raw_callee_save___kvm_vcpu_is_preempted:"
+FRAME_BEGIN
+"movq __per_cpu_offset(,%rdi,8), %rax;"
+"cmpb $0, 16+steal_time(%rax);"
+"setne %al;"
+FRAME_END
+"ret;"
+".popsection"
+);
+
+#endif
+
/*
* Setup pv_lock_ops to exploit KVM_FEATURE_PV_UNHALT if present.
*/
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Re: [Xen-devel] [PATCH v2] x86/paravirt: Don't make vcpu_is_preempted() a callee-save function
On 02/14/2017 04:39 AM, Peter Zijlstra wrote: > On Mon, Feb 13, 2017 at 05:34:01PM -0500, Waiman Long wrote: >> It is the address of &steal_time that will exceed the 32-bit limit. > That seems extremely unlikely. That would mean we have more than 4G > worth of per-cpu variables declared in the kernel. I have some doubt about if the compiler is able to properly use RIP-relative addressing for this. Anyway, it seems like constraints aren't allowed for asm() when not in the function context, at least for the the compiler that I am using (4.8.5). So it is a moot point. Cheers, Longman ___ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel
Re: [Xen-devel] [PATCH v2] x86/paravirt: Don't make vcpu_is_preempted() a callee-save function
On Mon, Feb 13, 2017 at 05:34:01PM -0500, Waiman Long wrote: > It is the address of &steal_time that will exceed the 32-bit limit. That seems extremely unlikely. That would mean we have more than 4G worth of per-cpu variables declared in the kernel. ___ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel
Re: [Xen-devel] [PATCH v2] x86/paravirt: Don't make vcpu_is_preempted() a callee-save function
On February 13, 2017 2:34:01 PM PST, Waiman Long wrote:
>On 02/13/2017 04:52 PM, Peter Zijlstra wrote:
>> On Mon, Feb 13, 2017 at 03:12:45PM -0500, Waiman Long wrote:
>>> On 02/13/2017 02:42 PM, Waiman Long wrote:
On 02/13/2017 05:53 AM, Peter Zijlstra wrote:
> On Mon, Feb 13, 2017 at 11:47:16AM +0100, Peter Zijlstra wrote:
>> That way we'd end up with something like:
>>
>> asm("
>> push %rdi;
>> movslq %edi, %rdi;
>> movq __per_cpu_offset(,%rdi,8), %rax;
>> cmpb $0, %[offset](%rax);
>> setne %al;
>> pop %rdi;
>> " : : [offset] "i" (((unsigned long)&steal_time) +
>offsetof(struct steal_time, preempted)));
>>
>> And if we could get rid of the sign extend on edi we could avoid
>all the
>> push-pop nonsense, but I'm not sure I see how to do that (then
>again,
>> this asm foo isn't my strongest point).
> Maybe:
>
> movsql %edi, %rax;
> movq __per_cpu_offset(,%rax,8), %rax;
> cmpb $0, %[offset](%rax);
> setne %al;
>
> ?
Yes, that looks good to me.
Cheers,
Longman
>>> Sorry, I am going to take it back. The displacement or offset can
>only
>>> be up to 32-bit. So we will still need to use at least one more
>>> register, I think.
>> I don't think that would be a problem, I very much doubt we declare
>more
>> than 4G worth of per-cpu variables in the kernel.
>>
>> In any case, use "e" or "Z" as constraint (I never quite know when to
>> use which). That are s32 and u32 displacement immediates resp. and
>> should fail compile with a semi-sensible failure if the displacement
>is
>> too big.
>>
>It is the address of &steal_time that will exceed the 32-bit limit.
>
>Cheers,
>Longman
That seems odd in the extreme?
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Re: [Xen-devel] [PATCH v2] x86/paravirt: Don't make vcpu_is_preempted() a callee-save function
On 02/13/2017 04:52 PM, Peter Zijlstra wrote:
> On Mon, Feb 13, 2017 at 03:12:45PM -0500, Waiman Long wrote:
>> On 02/13/2017 02:42 PM, Waiman Long wrote:
>>> On 02/13/2017 05:53 AM, Peter Zijlstra wrote:
On Mon, Feb 13, 2017 at 11:47:16AM +0100, Peter Zijlstra wrote:
> That way we'd end up with something like:
>
> asm("
> push %rdi;
> movslq %edi, %rdi;
> movq __per_cpu_offset(,%rdi,8), %rax;
> cmpb $0, %[offset](%rax);
> setne %al;
> pop %rdi;
> " : : [offset] "i" (((unsigned long)&steal_time) + offsetof(struct
> steal_time, preempted)));
>
> And if we could get rid of the sign extend on edi we could avoid all the
> push-pop nonsense, but I'm not sure I see how to do that (then again,
> this asm foo isn't my strongest point).
Maybe:
movsql %edi, %rax;
movq __per_cpu_offset(,%rax,8), %rax;
cmpb $0, %[offset](%rax);
setne %al;
?
>>> Yes, that looks good to me.
>>>
>>> Cheers,
>>> Longman
>>>
>> Sorry, I am going to take it back. The displacement or offset can only
>> be up to 32-bit. So we will still need to use at least one more
>> register, I think.
> I don't think that would be a problem, I very much doubt we declare more
> than 4G worth of per-cpu variables in the kernel.
>
> In any case, use "e" or "Z" as constraint (I never quite know when to
> use which). That are s32 and u32 displacement immediates resp. and
> should fail compile with a semi-sensible failure if the displacement is
> too big.
>
It is the address of &steal_time that will exceed the 32-bit limit.
Cheers,
Longman
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Re: [Xen-devel] [PATCH v2] x86/paravirt: Don't make vcpu_is_preempted() a callee-save function
On Mon, Feb 13, 2017 at 05:24:36PM -0500, Waiman Long wrote: > >> movsql %edi, %rax; > >> movq __per_cpu_offset(,%rax,8), %rax; > >> cmpb $0, %[offset](%rax); > >> setne %al; > I have thought of that too. However, the goal is to eliminate memory > read/write from/to stack. Eliminating a register sign-extend instruction > won't help much in term of performance. Problem here is that all instructions have dependencies, so if you can get rid of the sign extend mov you kill a bunch of stall cycles (I would expect). But yes, peanuts vs the stack load/stores. ___ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel
Re: [Xen-devel] [PATCH v2] x86/paravirt: Don't make vcpu_is_preempted() a callee-save function
On 02/13/2017 03:06 PM, h...@zytor.com wrote:
> On February 13, 2017 2:53:43 AM PST, Peter Zijlstra
> wrote:
>> On Mon, Feb 13, 2017 at 11:47:16AM +0100, Peter Zijlstra wrote:
>>> That way we'd end up with something like:
>>>
>>> asm("
>>> push %rdi;
>>> movslq %edi, %rdi;
>>> movq __per_cpu_offset(,%rdi,8), %rax;
>>> cmpb $0, %[offset](%rax);
>>> setne %al;
>>> pop %rdi;
>>> " : : [offset] "i" (((unsigned long)&steal_time) + offsetof(struct
>> steal_time, preempted)));
>>> And if we could get rid of the sign extend on edi we could avoid all
>> the
>>> push-pop nonsense, but I'm not sure I see how to do that (then again,
>>> this asm foo isn't my strongest point).
>> Maybe:
>>
>> movsql %edi, %rax;
>> movq __per_cpu_offset(,%rax,8), %rax;
>> cmpb $0, %[offset](%rax);
>> setne %al;
>>
>> ?
> We could kill the zero or sign extend by changing the calling interface to
> pass an unsigned long instead of an int. It is much more likely that a zero
> extend is free for the caller than a sign extend.
I have thought of that too. However, the goal is to eliminate memory
read/write from/to stack. Eliminating a register sign-extend instruction
won't help much in term of performance.
Cheers,
Longman
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Re: [Xen-devel] [PATCH v2] x86/paravirt: Don't make vcpu_is_preempted() a callee-save function
On February 13, 2017 1:52:20 PM PST, Peter Zijlstra
wrote:
>On Mon, Feb 13, 2017 at 03:12:45PM -0500, Waiman Long wrote:
>> On 02/13/2017 02:42 PM, Waiman Long wrote:
>> > On 02/13/2017 05:53 AM, Peter Zijlstra wrote:
>> >> On Mon, Feb 13, 2017 at 11:47:16AM +0100, Peter Zijlstra wrote:
>> >>> That way we'd end up with something like:
>> >>>
>> >>> asm("
>> >>> push %rdi;
>> >>> movslq %edi, %rdi;
>> >>> movq __per_cpu_offset(,%rdi,8), %rax;
>> >>> cmpb $0, %[offset](%rax);
>> >>> setne %al;
>> >>> pop %rdi;
>> >>> " : : [offset] "i" (((unsigned long)&steal_time) +
>offsetof(struct steal_time, preempted)));
>> >>>
>> >>> And if we could get rid of the sign extend on edi we could avoid
>all the
>> >>> push-pop nonsense, but I'm not sure I see how to do that (then
>again,
>> >>> this asm foo isn't my strongest point).
>> >> Maybe:
>> >>
>> >> movsql %edi, %rax;
>> >> movq __per_cpu_offset(,%rax,8), %rax;
>> >> cmpb $0, %[offset](%rax);
>> >> setne %al;
>> >>
>> >> ?
>> > Yes, that looks good to me.
>> >
>> > Cheers,
>> > Longman
>> >
>> Sorry, I am going to take it back. The displacement or offset can
>only
>> be up to 32-bit. So we will still need to use at least one more
>> register, I think.
>
>I don't think that would be a problem, I very much doubt we declare
>more
>than 4G worth of per-cpu variables in the kernel.
>
>In any case, use "e" or "Z" as constraint (I never quite know when to
>use which). That are s32 and u32 displacement immediates resp. and
>should fail compile with a semi-sensible failure if the displacement is
>too big.
Oh, and unless you are explicitly forcing 32-bit addressing mode, displacements
are always "e" (or "m" if you let gcc pick the addressing mode.)
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Re: [Xen-devel] [PATCH v2] x86/paravirt: Don't make vcpu_is_preempted() a callee-save function
On February 13, 2017 1:52:20 PM PST, Peter Zijlstra
wrote:
>On Mon, Feb 13, 2017 at 03:12:45PM -0500, Waiman Long wrote:
>> On 02/13/2017 02:42 PM, Waiman Long wrote:
>> > On 02/13/2017 05:53 AM, Peter Zijlstra wrote:
>> >> On Mon, Feb 13, 2017 at 11:47:16AM +0100, Peter Zijlstra wrote:
>> >>> That way we'd end up with something like:
>> >>>
>> >>> asm("
>> >>> push %rdi;
>> >>> movslq %edi, %rdi;
>> >>> movq __per_cpu_offset(,%rdi,8), %rax;
>> >>> cmpb $0, %[offset](%rax);
>> >>> setne %al;
>> >>> pop %rdi;
>> >>> " : : [offset] "i" (((unsigned long)&steal_time) +
>offsetof(struct steal_time, preempted)));
>> >>>
>> >>> And if we could get rid of the sign extend on edi we could avoid
>all the
>> >>> push-pop nonsense, but I'm not sure I see how to do that (then
>again,
>> >>> this asm foo isn't my strongest point).
>> >> Maybe:
>> >>
>> >> movsql %edi, %rax;
>> >> movq __per_cpu_offset(,%rax,8), %rax;
>> >> cmpb $0, %[offset](%rax);
>> >> setne %al;
>> >>
>> >> ?
>> > Yes, that looks good to me.
>> >
>> > Cheers,
>> > Longman
>> >
>> Sorry, I am going to take it back. The displacement or offset can
>only
>> be up to 32-bit. So we will still need to use at least one more
>> register, I think.
>
>I don't think that would be a problem, I very much doubt we declare
>more
>than 4G worth of per-cpu variables in the kernel.
>
>In any case, use "e" or "Z" as constraint (I never quite know when to
>use which). That are s32 and u32 displacement immediates resp. and
>should fail compile with a semi-sensible failure if the displacement is
>too big.
e for signed, Z for unsigned. Obviously you have to use a matching
instruction: an immediate or displacement in a 64-bit instruction is
sign-extended, in a 32-bit instruction zero-extended. E.g.:
movl %0,%%eax # use Z, all of %rax will be set
movq %0,%%rax # use e
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Re: [Xen-devel] [PATCH v2] x86/paravirt: Don't make vcpu_is_preempted() a callee-save function
On Mon, Feb 13, 2017 at 12:06:44PM -0800, h...@zytor.com wrote: > >Maybe: > > > >movsql %edi, %rax; > >movq __per_cpu_offset(,%rax,8), %rax; > >cmpb $0, %[offset](%rax); > >setne %al; > > > >? > > We could kill the zero or sign extend by changing the calling > interface to pass an unsigned long instead of an int. It is much more > likely that a zero extend is free for the caller than a sign extend. Right, Boris and me talked about that on IRC. I was wondering if the argument was u32 if we could assume the top 32 bits are 0 and then use rdi without prior movzx. That would allow reducing the thing one more instruction. Also, PVOP_CALL_ARG#() have an (unsigned long) cast in them that doesn't make sense. That cast ends up resulting in the calling code doing explicit sign or zero extends into the full 64bit register for no good reason. If one removes that cast things still compile, but I worry something somehow relies on this weird behaviour and will come apart. ___ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel
Re: [Xen-devel] [PATCH v2] x86/paravirt: Don't make vcpu_is_preempted() a callee-save function
On Mon, Feb 13, 2017 at 03:12:45PM -0500, Waiman Long wrote:
> On 02/13/2017 02:42 PM, Waiman Long wrote:
> > On 02/13/2017 05:53 AM, Peter Zijlstra wrote:
> >> On Mon, Feb 13, 2017 at 11:47:16AM +0100, Peter Zijlstra wrote:
> >>> That way we'd end up with something like:
> >>>
> >>> asm("
> >>> push %rdi;
> >>> movslq %edi, %rdi;
> >>> movq __per_cpu_offset(,%rdi,8), %rax;
> >>> cmpb $0, %[offset](%rax);
> >>> setne %al;
> >>> pop %rdi;
> >>> " : : [offset] "i" (((unsigned long)&steal_time) + offsetof(struct
> >>> steal_time, preempted)));
> >>>
> >>> And if we could get rid of the sign extend on edi we could avoid all the
> >>> push-pop nonsense, but I'm not sure I see how to do that (then again,
> >>> this asm foo isn't my strongest point).
> >> Maybe:
> >>
> >> movsql %edi, %rax;
> >> movq __per_cpu_offset(,%rax,8), %rax;
> >> cmpb $0, %[offset](%rax);
> >> setne %al;
> >>
> >> ?
> > Yes, that looks good to me.
> >
> > Cheers,
> > Longman
> >
> Sorry, I am going to take it back. The displacement or offset can only
> be up to 32-bit. So we will still need to use at least one more
> register, I think.
I don't think that would be a problem, I very much doubt we declare more
than 4G worth of per-cpu variables in the kernel.
In any case, use "e" or "Z" as constraint (I never quite know when to
use which). That are s32 and u32 displacement immediates resp. and
should fail compile with a semi-sensible failure if the displacement is
too big.
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Re: [Xen-devel] [PATCH v2] x86/paravirt: Don't make vcpu_is_preempted() a callee-save function
On 02/13/2017 02:42 PM, Waiman Long wrote:
> On 02/13/2017 05:53 AM, Peter Zijlstra wrote:
>> On Mon, Feb 13, 2017 at 11:47:16AM +0100, Peter Zijlstra wrote:
>>> That way we'd end up with something like:
>>>
>>> asm("
>>> push %rdi;
>>> movslq %edi, %rdi;
>>> movq __per_cpu_offset(,%rdi,8), %rax;
>>> cmpb $0, %[offset](%rax);
>>> setne %al;
>>> pop %rdi;
>>> " : : [offset] "i" (((unsigned long)&steal_time) + offsetof(struct
>>> steal_time, preempted)));
>>>
>>> And if we could get rid of the sign extend on edi we could avoid all the
>>> push-pop nonsense, but I'm not sure I see how to do that (then again,
>>> this asm foo isn't my strongest point).
>> Maybe:
>>
>> movsql %edi, %rax;
>> movq __per_cpu_offset(,%rax,8), %rax;
>> cmpb $0, %[offset](%rax);
>> setne %al;
>>
>> ?
> Yes, that looks good to me.
>
> Cheers,
> Longman
>
Sorry, I am going to take it back. The displacement or offset can only
be up to 32-bit. So we will still need to use at least one more
register, I think.
Cheers,
Longman
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Re: [Xen-devel] [PATCH v2] x86/paravirt: Don't make vcpu_is_preempted() a callee-save function
On February 13, 2017 2:53:43 AM PST, Peter Zijlstra
wrote:
>On Mon, Feb 13, 2017 at 11:47:16AM +0100, Peter Zijlstra wrote:
>> That way we'd end up with something like:
>>
>> asm("
>> push %rdi;
>> movslq %edi, %rdi;
>> movq __per_cpu_offset(,%rdi,8), %rax;
>> cmpb $0, %[offset](%rax);
>> setne %al;
>> pop %rdi;
>> " : : [offset] "i" (((unsigned long)&steal_time) + offsetof(struct
>steal_time, preempted)));
>>
>> And if we could get rid of the sign extend on edi we could avoid all
>the
>> push-pop nonsense, but I'm not sure I see how to do that (then again,
>> this asm foo isn't my strongest point).
>
>Maybe:
>
>movsql %edi, %rax;
>movq __per_cpu_offset(,%rax,8), %rax;
>cmpb $0, %[offset](%rax);
>setne %al;
>
>?
We could kill the zero or sign extend by changing the calling interface to pass
an unsigned long instead of an int. It is much more likely that a zero extend
is free for the caller than a sign extend.
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Re: [Xen-devel] [PATCH v2] x86/paravirt: Don't make vcpu_is_preempted() a callee-save function
On 02/13/2017 05:53 AM, Peter Zijlstra wrote:
> On Mon, Feb 13, 2017 at 11:47:16AM +0100, Peter Zijlstra wrote:
>> That way we'd end up with something like:
>>
>> asm("
>> push %rdi;
>> movslq %edi, %rdi;
>> movq __per_cpu_offset(,%rdi,8), %rax;
>> cmpb $0, %[offset](%rax);
>> setne %al;
>> pop %rdi;
>> " : : [offset] "i" (((unsigned long)&steal_time) + offsetof(struct
>> steal_time, preempted)));
>>
>> And if we could get rid of the sign extend on edi we could avoid all the
>> push-pop nonsense, but I'm not sure I see how to do that (then again,
>> this asm foo isn't my strongest point).
> Maybe:
>
> movsql %edi, %rax;
> movq __per_cpu_offset(,%rax,8), %rax;
> cmpb $0, %[offset](%rax);
> setne %al;
>
> ?
Yes, that looks good to me.
Cheers,
Longman
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Re: [Xen-devel] [PATCH v2] x86/paravirt: Don't make vcpu_is_preempted() a callee-save function
On 02/13/2017 05:47 AM, Peter Zijlstra wrote:
> On Fri, Feb 10, 2017 at 12:00:43PM -0500, Waiman Long wrote:
>
+asm(
+".pushsection .text;"
+".global __raw_callee_save___kvm_vcpu_is_preempted;"
+".type __raw_callee_save___kvm_vcpu_is_preempted, @function;"
+"__raw_callee_save___kvm_vcpu_is_preempted:"
+FRAME_BEGIN
+"push %rdi;"
+"push %rdx;"
+"movslq %edi, %rdi;"
+"movq$steal_time+16, %rax;"
+"movq__per_cpu_offset(,%rdi,8), %rdx;"
+"cmpb$0, (%rdx,%rax);"
> Could we not put the $steal_time+16 displacement as an immediate in the
> cmpb and save a whole register here?
>
> That way we'd end up with something like:
>
> asm("
> push %rdi;
> movslq %edi, %rdi;
> movq __per_cpu_offset(,%rdi,8), %rax;
> cmpb $0, %[offset](%rax);
> setne %al;
> pop %rdi;
> " : : [offset] "i" (((unsigned long)&steal_time) + offsetof(struct
> steal_time, preempted)));
>
> And if we could get rid of the sign extend on edi we could avoid all the
> push-pop nonsense, but I'm not sure I see how to do that (then again,
> this asm foo isn't my strongest point).
Yes, I think that can work. I will try to ran this patch to see how
thing goes.
+"setne %al;"
+"pop %rdx;"
+"pop %rdi;"
+FRAME_END
+"ret;"
+".popsection");
+
+#endif
+
/*
* Setup pv_lock_ops to exploit KVM_FEATURE_PV_UNHALT if present.
*/
>>> That should work for now. I have done something similar for
>>> __pv_queued_spin_unlock. However, this has the problem of creating a
>>> dependency on the exact layout of the steal_time structure. Maybe the
>>> constant 16 can be passed in as a parameter offsetof(struct
>>> kvm_steal_time, preempted) to the asm call.
> Yeah it should be well possible to pass that in. But ideally we'd have
> GCC grow something like __attribute__((callee_saved)) or somesuch and it
> would do all this for us.
That will be really nice too. I am not too fond of working in assembly.
>> One more thing, that will improve KVM performance, but it won't help Xen.
> People still use Xen? ;-) In any case, their implementation looks very
> similar and could easily crib this.
In Red Hat, my focus will be on KVM performance. I do believe that there
are still Xen users out there. So we still need to keep their interest
into consideration. Given that, I am OK to make it work better in KVM
first and then think about Xen later.
>> I looked into the assembly code for rwsem_spin_on_owner, It need to save
>> and restore 2 additional registers with my patch. Doing it your way,
>> will transfer the save and restore overhead to the assembly code.
>> However, __kvm_vcpu_is_preempted() is called multiple times per
>> invocation of rwsem_spin_on_owner. That function is simple enough that
>> making __kvm_vcpu_is_preempted() callee-save won't produce much compiler
>> optimization opportunity.
> This is because of that noinline, right? Otherwise it would've been
> folded and register pressure would be much higher.
Yes, I guess so. The noinline is there so that we know what the CPU time
is for spinning rather than other activities within the slowpath.
>
>> The outer function rwsem_down_write_failed()
>> does appear to be a bit bigger (from 866 bytes to 884 bytes) though.
> I suspect GCC is being clever and since all this is static it plays
> games with the calling convention and pushes these clobbers out.
>
>
Cheers,
Longman
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Re: [Xen-devel] [PATCH v2] x86/paravirt: Don't make vcpu_is_preempted() a callee-save function
On Mon, Feb 13, 2017 at 11:47:16AM +0100, Peter Zijlstra wrote:
> That way we'd end up with something like:
>
> asm("
> push %rdi;
> movslq %edi, %rdi;
> movq __per_cpu_offset(,%rdi,8), %rax;
> cmpb $0, %[offset](%rax);
> setne %al;
> pop %rdi;
> " : : [offset] "i" (((unsigned long)&steal_time) + offsetof(struct
> steal_time, preempted)));
>
> And if we could get rid of the sign extend on edi we could avoid all the
> push-pop nonsense, but I'm not sure I see how to do that (then again,
> this asm foo isn't my strongest point).
Maybe:
movsql %edi, %rax;
movq __per_cpu_offset(,%rax,8), %rax;
cmpb $0, %[offset](%rax);
setne %al;
?
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Re: [Xen-devel] [PATCH v2] x86/paravirt: Don't make vcpu_is_preempted() a callee-save function
On Fri, Feb 10, 2017 at 12:00:43PM -0500, Waiman Long wrote:
> >> +asm(
> >> +".pushsection .text;"
> >> +".global __raw_callee_save___kvm_vcpu_is_preempted;"
> >> +".type __raw_callee_save___kvm_vcpu_is_preempted, @function;"
> >> +"__raw_callee_save___kvm_vcpu_is_preempted:"
> >> +FRAME_BEGIN
> >> +"push %rdi;"
> >> +"push %rdx;"
> >> +"movslq %edi, %rdi;"
> >> +"movq$steal_time+16, %rax;"
> >> +"movq__per_cpu_offset(,%rdi,8), %rdx;"
> >> +"cmpb$0, (%rdx,%rax);"
Could we not put the $steal_time+16 displacement as an immediate in the
cmpb and save a whole register here?
That way we'd end up with something like:
asm("
push %rdi;
movslq %edi, %rdi;
movq __per_cpu_offset(,%rdi,8), %rax;
cmpb $0, %[offset](%rax);
setne %al;
pop %rdi;
" : : [offset] "i" (((unsigned long)&steal_time) + offsetof(struct steal_time,
preempted)));
And if we could get rid of the sign extend on edi we could avoid all the
push-pop nonsense, but I'm not sure I see how to do that (then again,
this asm foo isn't my strongest point).
> >> +"setne %al;"
> >> +"pop %rdx;"
> >> +"pop %rdi;"
> >> +FRAME_END
> >> +"ret;"
> >> +".popsection");
> >> +
> >> +#endif
> >> +
> >> /*
> >> * Setup pv_lock_ops to exploit KVM_FEATURE_PV_UNHALT if present.
> >> */
> > That should work for now. I have done something similar for
> > __pv_queued_spin_unlock. However, this has the problem of creating a
> > dependency on the exact layout of the steal_time structure. Maybe the
> > constant 16 can be passed in as a parameter offsetof(struct
> > kvm_steal_time, preempted) to the asm call.
Yeah it should be well possible to pass that in. But ideally we'd have
GCC grow something like __attribute__((callee_saved)) or somesuch and it
would do all this for us.
> One more thing, that will improve KVM performance, but it won't help Xen.
People still use Xen? ;-) In any case, their implementation looks very
similar and could easily crib this.
> I looked into the assembly code for rwsem_spin_on_owner, It need to save
> and restore 2 additional registers with my patch. Doing it your way,
> will transfer the save and restore overhead to the assembly code.
> However, __kvm_vcpu_is_preempted() is called multiple times per
> invocation of rwsem_spin_on_owner. That function is simple enough that
> making __kvm_vcpu_is_preempted() callee-save won't produce much compiler
> optimization opportunity.
This is because of that noinline, right? Otherwise it would've been
folded and register pressure would be much higher.
> The outer function rwsem_down_write_failed()
> does appear to be a bit bigger (from 866 bytes to 884 bytes) though.
I suspect GCC is being clever and since all this is static it plays
games with the calling convention and pushes these clobbers out.
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Re: [Xen-devel] [PATCH v2] x86/paravirt: Don't make vcpu_is_preempted() a callee-save function
On 02/10/2017 11:35 AM, Waiman Long wrote:
> On 02/10/2017 11:19 AM, Peter Zijlstra wrote:
>> On Fri, Feb 10, 2017 at 10:43:09AM -0500, Waiman Long wrote:
>>> It was found when running fio sequential write test with a XFS ramdisk
>>> on a VM running on a 2-socket x86-64 system, the %CPU times as reported
>>> by perf were as follows:
>>>
>>> 69.75% 0.59% fio [k] down_write
>>> 69.15% 0.01% fio [k] call_rwsem_down_write_failed
>>> 67.12% 1.12% fio [k] rwsem_down_write_failed
>>> 63.48% 52.77% fio [k] osq_lock
>>> 9.46% 7.88% fio [k] __raw_callee_save___kvm_vcpu_is_preempt
>>> 3.93% 3.93% fio [k] __kvm_vcpu_is_preempted
>>>
>> Thinking about this again, wouldn't something like the below also work?
>>
>>
>> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
>> index 099fcba4981d..6aa33702c15c 100644
>> --- a/arch/x86/kernel/kvm.c
>> +++ b/arch/x86/kernel/kvm.c
>> @@ -589,6 +589,7 @@ static void kvm_wait(u8 *ptr, u8 val)
>> local_irq_restore(flags);
>> }
>>
>> +#ifdef CONFIG_X86_32
>> __visible bool __kvm_vcpu_is_preempted(int cpu)
>> {
>> struct kvm_steal_time *src = &per_cpu(steal_time, cpu);
>> @@ -597,6 +598,31 @@ __visible bool __kvm_vcpu_is_preempted(int cpu)
>> }
>> PV_CALLEE_SAVE_REGS_THUNK(__kvm_vcpu_is_preempted);
>>
>> +#else
>> +
>> +extern bool __raw_callee_save___kvm_vcpu_is_preempted(int);
>> +
>> +asm(
>> +".pushsection .text;"
>> +".global __raw_callee_save___kvm_vcpu_is_preempted;"
>> +".type __raw_callee_save___kvm_vcpu_is_preempted, @function;"
>> +"__raw_callee_save___kvm_vcpu_is_preempted:"
>> +FRAME_BEGIN
>> +"push %rdi;"
>> +"push %rdx;"
>> +"movslq %edi, %rdi;"
>> +"movq$steal_time+16, %rax;"
>> +"movq__per_cpu_offset(,%rdi,8), %rdx;"
>> +"cmpb$0, (%rdx,%rax);"
>> +"setne %al;"
>> +"pop %rdx;"
>> +"pop %rdi;"
>> +FRAME_END
>> +"ret;"
>> +".popsection");
>> +
>> +#endif
>> +
>> /*
>> * Setup pv_lock_ops to exploit KVM_FEATURE_PV_UNHALT if present.
>> */
> That should work for now. I have done something similar for
> __pv_queued_spin_unlock. However, this has the problem of creating a
> dependency on the exact layout of the steal_time structure. Maybe the
> constant 16 can be passed in as a parameter offsetof(struct
> kvm_steal_time, preempted) to the asm call.
>
> Cheers,
> Longman
One more thing, that will improve KVM performance, but it won't help Xen.
I looked into the assembly code for rwsem_spin_on_owner, It need to save
and restore 2 additional registers with my patch. Doing it your way,
will transfer the save and restore overhead to the assembly code.
However, __kvm_vcpu_is_preempted() is called multiple times per
invocation of rwsem_spin_on_owner. That function is simple enough that
making __kvm_vcpu_is_preempted() callee-save won't produce much compiler
optimization opportunity. The outer function rwsem_down_write_failed()
does appear to be a bit bigger (from 866 bytes to 884 bytes) though.
Cheers,
Longman
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Re: [Xen-devel] [PATCH v2] x86/paravirt: Don't make vcpu_is_preempted() a callee-save function
On 02/10/2017 11:19 AM, Peter Zijlstra wrote:
> On Fri, Feb 10, 2017 at 10:43:09AM -0500, Waiman Long wrote:
>> It was found when running fio sequential write test with a XFS ramdisk
>> on a VM running on a 2-socket x86-64 system, the %CPU times as reported
>> by perf were as follows:
>>
>> 69.75% 0.59% fio [k] down_write
>> 69.15% 0.01% fio [k] call_rwsem_down_write_failed
>> 67.12% 1.12% fio [k] rwsem_down_write_failed
>> 63.48% 52.77% fio [k] osq_lock
>> 9.46% 7.88% fio [k] __raw_callee_save___kvm_vcpu_is_preempt
>> 3.93% 3.93% fio [k] __kvm_vcpu_is_preempted
>>
> Thinking about this again, wouldn't something like the below also work?
>
>
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index 099fcba4981d..6aa33702c15c 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -589,6 +589,7 @@ static void kvm_wait(u8 *ptr, u8 val)
> local_irq_restore(flags);
> }
>
> +#ifdef CONFIG_X86_32
> __visible bool __kvm_vcpu_is_preempted(int cpu)
> {
> struct kvm_steal_time *src = &per_cpu(steal_time, cpu);
> @@ -597,6 +598,31 @@ __visible bool __kvm_vcpu_is_preempted(int cpu)
> }
> PV_CALLEE_SAVE_REGS_THUNK(__kvm_vcpu_is_preempted);
>
> +#else
> +
> +extern bool __raw_callee_save___kvm_vcpu_is_preempted(int);
> +
> +asm(
> +".pushsection .text;"
> +".global __raw_callee_save___kvm_vcpu_is_preempted;"
> +".type __raw_callee_save___kvm_vcpu_is_preempted, @function;"
> +"__raw_callee_save___kvm_vcpu_is_preempted:"
> +FRAME_BEGIN
> +"push %rdi;"
> +"push %rdx;"
> +"movslq %edi, %rdi;"
> +"movq$steal_time+16, %rax;"
> +"movq__per_cpu_offset(,%rdi,8), %rdx;"
> +"cmpb$0, (%rdx,%rax);"
> +"setne %al;"
> +"pop %rdx;"
> +"pop %rdi;"
> +FRAME_END
> +"ret;"
> +".popsection");
> +
> +#endif
> +
> /*
> * Setup pv_lock_ops to exploit KVM_FEATURE_PV_UNHALT if present.
> */
That should work for now. I have done something similar for
__pv_queued_spin_unlock. However, this has the problem of creating a
dependency on the exact layout of the steal_time structure. Maybe the
constant 16 can be passed in as a parameter offsetof(struct
kvm_steal_time, preempted) to the asm call.
Cheers,
Longman
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Re: [Xen-devel] [PATCH v2] x86/paravirt: Don't make vcpu_is_preempted() a callee-save function
On 10/02/2017 16:43, Waiman Long wrote:
> It was found when running fio sequential write test with a XFS ramdisk
> on a VM running on a 2-socket x86-64 system, the %CPU times as reported
> by perf were as follows:
>
> 69.75% 0.59% fio [k] down_write
> 69.15% 0.01% fio [k] call_rwsem_down_write_failed
> 67.12% 1.12% fio [k] rwsem_down_write_failed
> 63.48% 52.77% fio [k] osq_lock
> 9.46% 7.88% fio [k] __raw_callee_save___kvm_vcpu_is_preempt
> 3.93% 3.93% fio [k] __kvm_vcpu_is_preempted
>
> Making vcpu_is_preempted() a callee-save function has a relatively
> high cost on x86-64 primarily due to at least one more cacheline of
> data access from the saving and restoring of registers (8 of them)
> to and from stack as well as one more level of function call. As
> vcpu_is_preempted() is called within the spinlock, mutex and rwsem
> slowpaths, there isn't much to gain by making it callee-save. So it
> is now changed to a normal function call instead.
>
> With this patch applied on both bare-metal & KVM guest on a 2-socekt
> 16-core 32-thread system with 16 parallel jobs (8 on each socket), the
> aggregrate bandwidth of the fio test on an XFS ramdisk were as follows:
>
>Bare MetalKVM Guest
>I/O Type w/o patchwith patch w/o patchwith patch
> --- ---
>random read 8650.5 MB/s 8560.9 MB/s 7602.9 MB/s 8196.1 MB/s
>seq read 9104.8 MB/s 9397.2 MB/s 8293.7 MB/s 8566.9 MB/s
>random write 1623.8 MB/s 1626.7 MB/s 1590.6 MB/s 1700.7 MB/s
>seq write 1626.4 MB/s 1624.9 MB/s 1604.8 MB/s 1726.3 MB/s
>
> The perf data (on KVM guest) now became:
>
> 70.78% 0.58% fio [k] down_write
> 70.20% 0.01% fio [k] call_rwsem_down_write_failed
> 69.70% 1.17% fio [k] rwsem_down_write_failed
> 59.91% 55.42% fio [k] osq_lock
> 10.14% 10.14% fio [k] __kvm_vcpu_is_preempted
>
> On bare metal, the patch doesn't introduce any performance
> regression. On KVM guest, it produces noticeable performance
> improvement (up to 7%).
>
> Signed-off-by: Waiman Long
> ---
> v1->v2:
> - Rerun the fio test on a different system on both bare-metal and a
> KVM guest. Both sockets were utilized in this test.
> - The commit log was updated with new performance numbers, but the
> patch wasn't changed.
> - Drop patch 2.
>
> arch/x86/include/asm/paravirt.h | 2 +-
> arch/x86/include/asm/paravirt_types.h | 2 +-
> arch/x86/kernel/kvm.c | 7 ++-
> arch/x86/kernel/paravirt-spinlocks.c | 6 ++
> arch/x86/xen/spinlock.c | 4 +---
> 5 files changed, 7 insertions(+), 14 deletions(-)
>
> diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
> index 864f57b..2515885 100644
> --- a/arch/x86/include/asm/paravirt.h
> +++ b/arch/x86/include/asm/paravirt.h
> @@ -676,7 +676,7 @@ static __always_inline void pv_kick(int cpu)
>
> static __always_inline bool pv_vcpu_is_preempted(int cpu)
> {
> - return PVOP_CALLEE1(bool, pv_lock_ops.vcpu_is_preempted, cpu);
> + return PVOP_CALL1(bool, pv_lock_ops.vcpu_is_preempted, cpu);
> }
>
> #endif /* SMP && PARAVIRT_SPINLOCKS */
> diff --git a/arch/x86/include/asm/paravirt_types.h
> b/arch/x86/include/asm/paravirt_types.h
> index bb2de45..88dc852 100644
> --- a/arch/x86/include/asm/paravirt_types.h
> +++ b/arch/x86/include/asm/paravirt_types.h
> @@ -309,7 +309,7 @@ struct pv_lock_ops {
> void (*wait)(u8 *ptr, u8 val);
> void (*kick)(int cpu);
>
> - struct paravirt_callee_save vcpu_is_preempted;
> + bool (*vcpu_is_preempted)(int cpu);
> };
>
> /* This contains all the paravirt structures: we get a convenient
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index 099fcba..eb3753d 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -595,7 +595,6 @@ __visible bool __kvm_vcpu_is_preempted(int cpu)
>
> return !!src->preempted;
> }
> -PV_CALLEE_SAVE_REGS_THUNK(__kvm_vcpu_is_preempted);
>
> /*
> * Setup pv_lock_ops to exploit KVM_FEATURE_PV_UNHALT if present.
> @@ -614,10 +613,8 @@ void __init kvm_spinlock_init(void)
> pv_lock_ops.wait = kvm_wait;
> pv_lock_ops.kick = kvm_kick_cpu;
>
> - if (kvm_para_has_feature(KVM_FEATURE_STEAL_TIME)) {
> - pv_lock_ops.vcpu_is_preempted =
> - PV_CALLEE_SAVE(__kvm_vcpu_is_preempted);
> - }
> + if (kvm_para_has_feature(KVM_FEATURE_STEAL_TIME))
> + pv_lock_ops.vcpu_is_preempted = __kvm_vcpu_is_preempted;
> }
>
> #endif /* CONFIG_PARAVIRT_SPINLOCKS */
> diff --git a/arch/x86/kernel/paravirt-spinlocks.c
> b/arch/x86/kernel/paravirt-spinlocks.c
> index 6259327..da050bc 100644
> --- a/arch/x86/kernel/paravirt-spinlocks.c
> +++ b/arch/x86/kernel/paravirt-spinlocks.c
> @@ -24,12 +24,10 @@ __visible bool __native_vcpu_is_preempted(int cpu)
> {
> return false;
>
Re: [Xen-devel] [PATCH v2] x86/paravirt: Don't make vcpu_is_preempted() a callee-save function
On Fri, Feb 10, 2017 at 10:43:09AM -0500, Waiman Long wrote:
> It was found when running fio sequential write test with a XFS ramdisk
> on a VM running on a 2-socket x86-64 system, the %CPU times as reported
> by perf were as follows:
>
> 69.75% 0.59% fio [k] down_write
> 69.15% 0.01% fio [k] call_rwsem_down_write_failed
> 67.12% 1.12% fio [k] rwsem_down_write_failed
> 63.48% 52.77% fio [k] osq_lock
> 9.46% 7.88% fio [k] __raw_callee_save___kvm_vcpu_is_preempt
> 3.93% 3.93% fio [k] __kvm_vcpu_is_preempted
>
Thinking about this again, wouldn't something like the below also work?
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 099fcba4981d..6aa33702c15c 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -589,6 +589,7 @@ static void kvm_wait(u8 *ptr, u8 val)
local_irq_restore(flags);
}
+#ifdef CONFIG_X86_32
__visible bool __kvm_vcpu_is_preempted(int cpu)
{
struct kvm_steal_time *src = &per_cpu(steal_time, cpu);
@@ -597,6 +598,31 @@ __visible bool __kvm_vcpu_is_preempted(int cpu)
}
PV_CALLEE_SAVE_REGS_THUNK(__kvm_vcpu_is_preempted);
+#else
+
+extern bool __raw_callee_save___kvm_vcpu_is_preempted(int);
+
+asm(
+".pushsection .text;"
+".global __raw_callee_save___kvm_vcpu_is_preempted;"
+".type __raw_callee_save___kvm_vcpu_is_preempted, @function;"
+"__raw_callee_save___kvm_vcpu_is_preempted:"
+FRAME_BEGIN
+"push %rdi;"
+"push %rdx;"
+"movslq %edi, %rdi;"
+"movq$steal_time+16, %rax;"
+"movq__per_cpu_offset(,%rdi,8), %rdx;"
+"cmpb$0, (%rdx,%rax);"
+"setne %al;"
+"pop %rdx;"
+"pop %rdi;"
+FRAME_END
+"ret;"
+".popsection");
+
+#endif
+
/*
* Setup pv_lock_ops to exploit KVM_FEATURE_PV_UNHALT if present.
*/
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[Xen-devel] [PATCH v2] x86/paravirt: Don't make vcpu_is_preempted() a callee-save function
It was found when running fio sequential write test with a XFS ramdisk
on a VM running on a 2-socket x86-64 system, the %CPU times as reported
by perf were as follows:
69.75% 0.59% fio [k] down_write
69.15% 0.01% fio [k] call_rwsem_down_write_failed
67.12% 1.12% fio [k] rwsem_down_write_failed
63.48% 52.77% fio [k] osq_lock
9.46% 7.88% fio [k] __raw_callee_save___kvm_vcpu_is_preempt
3.93% 3.93% fio [k] __kvm_vcpu_is_preempted
Making vcpu_is_preempted() a callee-save function has a relatively
high cost on x86-64 primarily due to at least one more cacheline of
data access from the saving and restoring of registers (8 of them)
to and from stack as well as one more level of function call. As
vcpu_is_preempted() is called within the spinlock, mutex and rwsem
slowpaths, there isn't much to gain by making it callee-save. So it
is now changed to a normal function call instead.
With this patch applied on both bare-metal & KVM guest on a 2-socekt
16-core 32-thread system with 16 parallel jobs (8 on each socket), the
aggregrate bandwidth of the fio test on an XFS ramdisk were as follows:
Bare MetalKVM Guest
I/O Type w/o patchwith patch w/o patchwith patch
--- ---
random read 8650.5 MB/s 8560.9 MB/s 7602.9 MB/s 8196.1 MB/s
seq read 9104.8 MB/s 9397.2 MB/s 8293.7 MB/s 8566.9 MB/s
random write 1623.8 MB/s 1626.7 MB/s 1590.6 MB/s 1700.7 MB/s
seq write 1626.4 MB/s 1624.9 MB/s 1604.8 MB/s 1726.3 MB/s
The perf data (on KVM guest) now became:
70.78% 0.58% fio [k] down_write
70.20% 0.01% fio [k] call_rwsem_down_write_failed
69.70% 1.17% fio [k] rwsem_down_write_failed
59.91% 55.42% fio [k] osq_lock
10.14% 10.14% fio [k] __kvm_vcpu_is_preempted
On bare metal, the patch doesn't introduce any performance
regression. On KVM guest, it produces noticeable performance
improvement (up to 7%).
Signed-off-by: Waiman Long
---
v1->v2:
- Rerun the fio test on a different system on both bare-metal and a
KVM guest. Both sockets were utilized in this test.
- The commit log was updated with new performance numbers, but the
patch wasn't changed.
- Drop patch 2.
arch/x86/include/asm/paravirt.h | 2 +-
arch/x86/include/asm/paravirt_types.h | 2 +-
arch/x86/kernel/kvm.c | 7 ++-
arch/x86/kernel/paravirt-spinlocks.c | 6 ++
arch/x86/xen/spinlock.c | 4 +---
5 files changed, 7 insertions(+), 14 deletions(-)
diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index 864f57b..2515885 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -676,7 +676,7 @@ static __always_inline void pv_kick(int cpu)
static __always_inline bool pv_vcpu_is_preempted(int cpu)
{
- return PVOP_CALLEE1(bool, pv_lock_ops.vcpu_is_preempted, cpu);
+ return PVOP_CALL1(bool, pv_lock_ops.vcpu_is_preempted, cpu);
}
#endif /* SMP && PARAVIRT_SPINLOCKS */
diff --git a/arch/x86/include/asm/paravirt_types.h
b/arch/x86/include/asm/paravirt_types.h
index bb2de45..88dc852 100644
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -309,7 +309,7 @@ struct pv_lock_ops {
void (*wait)(u8 *ptr, u8 val);
void (*kick)(int cpu);
- struct paravirt_callee_save vcpu_is_preempted;
+ bool (*vcpu_is_preempted)(int cpu);
};
/* This contains all the paravirt structures: we get a convenient
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 099fcba..eb3753d 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -595,7 +595,6 @@ __visible bool __kvm_vcpu_is_preempted(int cpu)
return !!src->preempted;
}
-PV_CALLEE_SAVE_REGS_THUNK(__kvm_vcpu_is_preempted);
/*
* Setup pv_lock_ops to exploit KVM_FEATURE_PV_UNHALT if present.
@@ -614,10 +613,8 @@ void __init kvm_spinlock_init(void)
pv_lock_ops.wait = kvm_wait;
pv_lock_ops.kick = kvm_kick_cpu;
- if (kvm_para_has_feature(KVM_FEATURE_STEAL_TIME)) {
- pv_lock_ops.vcpu_is_preempted =
- PV_CALLEE_SAVE(__kvm_vcpu_is_preempted);
- }
+ if (kvm_para_has_feature(KVM_FEATURE_STEAL_TIME))
+ pv_lock_ops.vcpu_is_preempted = __kvm_vcpu_is_preempted;
}
#endif /* CONFIG_PARAVIRT_SPINLOCKS */
diff --git a/arch/x86/kernel/paravirt-spinlocks.c
b/arch/x86/kernel/paravirt-spinlocks.c
index 6259327..da050bc 100644
--- a/arch/x86/kernel/paravirt-spinlocks.c
+++ b/arch/x86/kernel/paravirt-spinlocks.c
@@ -24,12 +24,10 @@ __visible bool __native_vcpu_is_preempted(int cpu)
{
return false;
}
-PV_CALLEE_SAVE_REGS_THUNK(__native_vcpu_is_preempted);
bool pv_is_native_vcpu_is_preempted(void)
{
- return pv_lock_ops.vcpu_is_preempted.func ==
- __raw_callee_save___native_vcpu_is_preempted;
+ return pv_lock_ops.vcpu_i
