Re: [PATCH] KVM: PPC: e500mc: Relax tlb invalidation condition on vcpu schedule
On 13.06.14 21:42, Scott Wood wrote: On Fri, 2014-06-13 at 16:55 +0200, Alexander Graf wrote: On 13.06.14 16:43, mihai.cara...@freescale.com wrote: -Original Message- From: Alexander Graf [mailto:ag...@suse.de] Sent: Thursday, June 12, 2014 8:05 PM To: Caraman Mihai Claudiu-B02008 Cc: kvm-...@vger.kernel.org; k...@vger.kernel.org; linuxppc- d...@lists.ozlabs.org; Wood Scott-B07421 Subject: Re: [PATCH] KVM: PPC: e500mc: Relax tlb invalidation condition on vcpu schedule On 06/12/2014 04:00 PM, Mihai Caraman wrote: On vcpu schedule, the condition checked for tlb pollution is too tight. The tlb entries of one vcpu are polluted when a different vcpu from the same partition runs in-between. Relax the current tlb invalidation condition taking into account the lpid. Can you quantify the performance improvement from this? We've had bugs in this area before, so let's make sure it's worth it before making this more complicated. Signed-off-by: Mihai Caraman mihai.caraman at freescale.com Your mailer is broken? :) This really should be an @. I think this should work. Scott, please ack. Alex, you were right. I screwed up the patch description by inverting relax and tight terms :) It should have been more like this: KVM: PPC: e500mc: Enhance tlb invalidation condition on vcpu schedule On vcpu schedule, the condition checked for tlb pollution is too loose. The tlb entries of a vcpu are polluted (vs stale) only when a different vcpu within the same logical partition runs in-between. Optimize the tlb invalidation condition taking into account the lpid. Can't we give every vcpu its own lpid? Or don't we trap on global invalidates? That would significantly increase the odds of exhausting LPIDs, especially on large chips like t4240 with similarly large VMs. If we were to do that, the LPIDs would need to be dynamically assigned (like PIDs), and should probably be a separate numberspace per physical core. True, I didn't realize we only have so few of them. It would however save us from most flushing as long as we have spare LPIDs available :). Alex ___ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
RE: [PATCH] KVM: PPC: e500mc: Relax tlb invalidation condition on vcpu schedule
-Original Message- From: Alexander Graf [mailto:ag...@suse.de] Sent: Tuesday, June 17, 2014 12:09 PM To: Wood Scott-B07421 Cc: Caraman Mihai Claudiu-B02008; kvm-...@vger.kernel.org; k...@vger.kernel.org; linuxppc-dev@lists.ozlabs.org Subject: Re: [PATCH] KVM: PPC: e500mc: Relax tlb invalidation condition on vcpu schedule On 13.06.14 21:42, Scott Wood wrote: On Fri, 2014-06-13 at 16:55 +0200, Alexander Graf wrote: On 13.06.14 16:43, mihai.cara...@freescale.com wrote: -Original Message- From: Alexander Graf [mailto:ag...@suse.de] Sent: Thursday, June 12, 2014 8:05 PM To: Caraman Mihai Claudiu-B02008 Cc: kvm-...@vger.kernel.org; k...@vger.kernel.org; linuxppc- d...@lists.ozlabs.org; Wood Scott-B07421 Subject: Re: [PATCH] KVM: PPC: e500mc: Relax tlb invalidation condition on vcpu schedule On 06/12/2014 04:00 PM, Mihai Caraman wrote: On vcpu schedule, the condition checked for tlb pollution is too tight. The tlb entries of one vcpu are polluted when a different vcpu from the same partition runs in-between. Relax the current tlb invalidation condition taking into account the lpid. Can you quantify the performance improvement from this? We've had bugs in this area before, so let's make sure it's worth it before making this more complicated. Signed-off-by: Mihai Caraman mihai.caraman at freescale.com Your mailer is broken? :) This really should be an @. I think this should work. Scott, please ack. Alex, you were right. I screwed up the patch description by inverting relax and tight terms :) It should have been more like this: KVM: PPC: e500mc: Enhance tlb invalidation condition on vcpu schedule On vcpu schedule, the condition checked for tlb pollution is too loose. The tlb entries of a vcpu are polluted (vs stale) only when a different vcpu within the same logical partition runs in-between. Optimize the tlb invalidation condition taking into account the lpid. Can't we give every vcpu its own lpid? Or don't we trap on global invalidates? That would significantly increase the odds of exhausting LPIDs, especially on large chips like t4240 with similarly large VMs. If we were to do that, the LPIDs would need to be dynamically assigned (like PIDs), and should probably be a separate numberspace per physical core. True, I didn't realize we only have so few of them. It would however save us from most flushing as long as we have spare LPIDs available :). Yes, we had this proposal on the table for e6500 multithreaded core. This core lacks tlb write conditional instruction, so an OS needs to use locks to protect itself against concurrent tlb writes executed from sibling threads. When we expose hw treads as single-threaded vcpus (useful when the user opt not to pin vcpus), the guest can't no longer protect itself optimally (it can protect tlb writes across all threads but this is not acceptable). So instead, we found a solution at hypervisor level by assigning different logical partition ids to guest's vcpus running simultaneous on sibling hw threads. Currently in FSL SDK we allocate two lpids to each guest. I am also a proponent for using all LPID space (63 values) per (multi-threaded) physical core, which will lead to fewer invalidates on vcpu schedule and will accommodate the solution described above. -Mike ___ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
Re: [PATCH] KVM: PPC: e500mc: Relax tlb invalidation condition on vcpu schedule
On Thu, 2014-06-12 at 19:04 +0200, Alexander Graf wrote:
On 06/12/2014 04:00 PM, Mihai Caraman wrote:
@@ -140,12 +142,24 @@ static void kvmppc_core_vcpu_load_e500mc(struct
kvm_vcpu *vcpu, int cpu)
mtspr(SPRN_GDEAR, vcpu-arch.shared-dar);
mtspr(SPRN_GESR, vcpu-arch.shared-esr);
- if (vcpu-arch.oldpir != mfspr(SPRN_PIR) ||
- __get_cpu_var(last_vcpu_on_cpu) != vcpu) {
- kvmppc_e500_tlbil_all(vcpu_e500);
+ if (vcpu-arch.oldpir != mfspr(SPRN_PIR)) {
+ /* tlb entries deprecated */
+ inval_tlb = update_last = true;
+ } else if (__get_cpu_var(last_vcpu_on_cpu) != vcpu) {
+ update_last = true;
+ /* tlb entries polluted */
+ inval_tlb = __get_cpu_var(last_lpid_on_cpu) ==
+ vcpu-kvm-arch.lpid;
+ }
What about the following sequence on one CPU:
LPID 1, vcpu A
LPID 2, vcpu C
LPID 1, vcpu B
LPID 2, vcpu C doesn't invalidate
LPID 1, vcpu A doesn't invalidate
In the last line, vcpu A last ran on this cpu (oldpir matches), but LPID
2 last ran on this cpu (last_lpid_on_cpu does not match) -- but an
invalidation has never happened since vcpu B from LPID 1 ran on this
cpu.
-Scott
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RE: [PATCH] KVM: PPC: e500mc: Relax tlb invalidation condition on vcpu schedule
-Original Message- From: Alexander Graf [mailto:ag...@suse.de] Sent: Thursday, June 12, 2014 8:05 PM To: Caraman Mihai Claudiu-B02008 Cc: kvm-...@vger.kernel.org; k...@vger.kernel.org; linuxppc- d...@lists.ozlabs.org; Wood Scott-B07421 Subject: Re: [PATCH] KVM: PPC: e500mc: Relax tlb invalidation condition on vcpu schedule On 06/12/2014 04:00 PM, Mihai Caraman wrote: On vcpu schedule, the condition checked for tlb pollution is too tight. The tlb entries of one vcpu are polluted when a different vcpu from the same partition runs in-between. Relax the current tlb invalidation condition taking into account the lpid. Signed-off-by: Mihai Caraman mihai.caraman at freescale.com Your mailer is broken? :) This really should be an @. I think this should work. Scott, please ack. Alex, you were right. I screwed up the patch description by inverting relax and tight terms :) It should have been more like this: KVM: PPC: e500mc: Enhance tlb invalidation condition on vcpu schedule On vcpu schedule, the condition checked for tlb pollution is too loose. The tlb entries of a vcpu are polluted (vs stale) only when a different vcpu within the same logical partition runs in-between. Optimize the tlb invalidation condition taking into account the lpid. -Mike ___ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
Re: [PATCH] KVM: PPC: e500mc: Relax tlb invalidation condition on vcpu schedule
On 13.06.14 16:43, mihai.cara...@freescale.com wrote: -Original Message- From: Alexander Graf [mailto:ag...@suse.de] Sent: Thursday, June 12, 2014 8:05 PM To: Caraman Mihai Claudiu-B02008 Cc: kvm-...@vger.kernel.org; k...@vger.kernel.org; linuxppc- d...@lists.ozlabs.org; Wood Scott-B07421 Subject: Re: [PATCH] KVM: PPC: e500mc: Relax tlb invalidation condition on vcpu schedule On 06/12/2014 04:00 PM, Mihai Caraman wrote: On vcpu schedule, the condition checked for tlb pollution is too tight. The tlb entries of one vcpu are polluted when a different vcpu from the same partition runs in-between. Relax the current tlb invalidation condition taking into account the lpid. Signed-off-by: Mihai Caraman mihai.caraman at freescale.com Your mailer is broken? :) This really should be an @. I think this should work. Scott, please ack. Alex, you were right. I screwed up the patch description by inverting relax and tight terms :) It should have been more like this: KVM: PPC: e500mc: Enhance tlb invalidation condition on vcpu schedule On vcpu schedule, the condition checked for tlb pollution is too loose. The tlb entries of a vcpu are polluted (vs stale) only when a different vcpu within the same logical partition runs in-between. Optimize the tlb invalidation condition taking into account the lpid. Can't we give every vcpu its own lpid? Or don't we trap on global invalidates? Alex ___ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
Re: [PATCH] KVM: PPC: e500mc: Relax tlb invalidation condition on vcpu schedule
On Fri, 2014-06-13 at 16:55 +0200, Alexander Graf wrote: On 13.06.14 16:43, mihai.cara...@freescale.com wrote: -Original Message- From: Alexander Graf [mailto:ag...@suse.de] Sent: Thursday, June 12, 2014 8:05 PM To: Caraman Mihai Claudiu-B02008 Cc: kvm-...@vger.kernel.org; k...@vger.kernel.org; linuxppc- d...@lists.ozlabs.org; Wood Scott-B07421 Subject: Re: [PATCH] KVM: PPC: e500mc: Relax tlb invalidation condition on vcpu schedule On 06/12/2014 04:00 PM, Mihai Caraman wrote: On vcpu schedule, the condition checked for tlb pollution is too tight. The tlb entries of one vcpu are polluted when a different vcpu from the same partition runs in-between. Relax the current tlb invalidation condition taking into account the lpid. Can you quantify the performance improvement from this? We've had bugs in this area before, so let's make sure it's worth it before making this more complicated. Signed-off-by: Mihai Caraman mihai.caraman at freescale.com Your mailer is broken? :) This really should be an @. I think this should work. Scott, please ack. Alex, you were right. I screwed up the patch description by inverting relax and tight terms :) It should have been more like this: KVM: PPC: e500mc: Enhance tlb invalidation condition on vcpu schedule On vcpu schedule, the condition checked for tlb pollution is too loose. The tlb entries of a vcpu are polluted (vs stale) only when a different vcpu within the same logical partition runs in-between. Optimize the tlb invalidation condition taking into account the lpid. Can't we give every vcpu its own lpid? Or don't we trap on global invalidates? That would significantly increase the odds of exhausting LPIDs, especially on large chips like t4240 with similarly large VMs. If we were to do that, the LPIDs would need to be dynamically assigned (like PIDs), and should probably be a separate numberspace per physical core. -Scott ___ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
Re: [PATCH] KVM: PPC: e500mc: Relax tlb invalidation condition on vcpu schedule
On 06/12/2014 04:00 PM, Mihai Caraman wrote:
On vcpu schedule, the condition checked for tlb pollution is too tight.
The tlb entries of one vcpu are polluted when a different vcpu from the
same partition runs in-between. Relax the current tlb invalidation
condition taking into account the lpid.
Signed-off-by: Mihai Caraman mihai.caraman at freescale.com
Your mailer is broken? :)
This really should be an @.
I think this should work. Scott, please ack.
Alex
Cc: Scott Wood scottwood at freescale.com
---
arch/powerpc/kvm/e500mc.c | 20 +---
1 file changed, 17 insertions(+), 3 deletions(-)
diff --git a/arch/powerpc/kvm/e500mc.c b/arch/powerpc/kvm/e500mc.c
index 17e4562..2e0cd69 100644
--- a/arch/powerpc/kvm/e500mc.c
+++ b/arch/powerpc/kvm/e500mc.c
@@ -111,10 +111,12 @@ void kvmppc_mmu_msr_notify(struct kvm_vcpu *vcpu, u32
old_msr)
}
static DEFINE_PER_CPU(struct kvm_vcpu *, last_vcpu_on_cpu);
+static DEFINE_PER_CPU(int, last_lpid_on_cpu);
static void kvmppc_core_vcpu_load_e500mc(struct kvm_vcpu *vcpu, int cpu)
{
struct kvmppc_vcpu_e500 *vcpu_e500 = to_e500(vcpu);
+ bool update_last = false, inval_tlb = false;
kvmppc_booke_vcpu_load(vcpu, cpu);
@@ -140,12 +142,24 @@ static void kvmppc_core_vcpu_load_e500mc(struct kvm_vcpu *vcpu, int cpu)
mtspr(SPRN_GDEAR, vcpu-arch.shared-dar);
mtspr(SPRN_GESR, vcpu-arch.shared-esr);
- if (vcpu-arch.oldpir != mfspr(SPRN_PIR) ||
- __get_cpu_var(last_vcpu_on_cpu) != vcpu) {
- kvmppc_e500_tlbil_all(vcpu_e500);
+ if (vcpu-arch.oldpir != mfspr(SPRN_PIR)) {
+ /* tlb entries deprecated */
+ inval_tlb = update_last = true;
+ } else if (__get_cpu_var(last_vcpu_on_cpu) != vcpu) {
+ update_last = true;
+ /* tlb entries polluted */
+ inval_tlb = __get_cpu_var(last_lpid_on_cpu) ==
+ vcpu-kvm-arch.lpid;
+ }
+
+ if (update_last) {
__get_cpu_var(last_vcpu_on_cpu) = vcpu;
+ __get_cpu_var(last_lpid_on_cpu) = vcpu-kvm-arch.lpid;
}
+ if (inval_tlb)
+ kvmppc_e500_tlbil_all(vcpu_e500);
+
kvmppc_load_guest_fp(vcpu);
}
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