Re: [patch 11/11] x66/vdso: Add CLOCK_TAI support
On Fri, 14 Sep 2018, Andy Lutomirski wrote: > > On Sep 14, 2018, at 7:27 AM, Thomas Gleixner wrote: > > On Fri, 14 Sep 2018, Andy Lutomirski wrote: > >> That’s... horrible. In an amazing way. Can you add BUILD_BUG_ON somewhere > >> to assert that this actually works? > > > > Sure, but changing any of the clock ids will cause more wreckage than that. > > > I’m more concerned that we add a new one and break the magic > masking. Maybe two start sharing the same slot. You are right. The obvious extension is CLOCK_BOOTTIME. That's id 7 which indeed conflicts. I'll remove the magic. Thanks, tglx___ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization
Re: [patch 11/11] x66/vdso: Add CLOCK_TAI support
> On Sep 14, 2018, at 7:27 AM, Thomas Gleixner wrote: > > On Fri, 14 Sep 2018, Andy Lutomirski wrote: >>> On Sep 14, 2018, at 5:50 AM, Thomas Gleixner wrote: >>> >>> With the storage array in place it's now trivial to support CLOCK_TAI in >>> the vdso. Instead of extending the array to accomodate CLOCK_TAI, make use >>> of the fact that: >>> >>> - CLOCK ids are set in stone >>> - CLOCK_THREAD_CPUTIME is never going to be supported in the VDSO so >>> the array slot 3 is unused >>> - CLOCK_TAI is id 11 which results in 3 when masked with 0x3 >>> >>> Add the mask to the basetime array lookup and set up the CLOCK_TAI base >>> time in update_vsyscall(). >> >> That’s... horrible. In an amazing way. Can you add BUILD_BUG_ON somewhere >> to assert that this actually works? > > Sure, but changing any of the clock ids will cause more wreckage than that. > I’m more concerned that we add a new one and break the magic masking. Maybe two start sharing the same slot. > Thanks, > >tglx ___ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization
Re: [patch 11/11] x66/vdso: Add CLOCK_TAI support
On Fri, 14 Sep 2018, Andy Lutomirski wrote: > > On Sep 14, 2018, at 5:50 AM, Thomas Gleixner wrote: > > > > With the storage array in place it's now trivial to support CLOCK_TAI in > > the vdso. Instead of extending the array to accomodate CLOCK_TAI, make use > > of the fact that: > > > > - CLOCK ids are set in stone > > - CLOCK_THREAD_CPUTIME is never going to be supported in the VDSO so > > the array slot 3 is unused > > - CLOCK_TAI is id 11 which results in 3 when masked with 0x3 > > > > Add the mask to the basetime array lookup and set up the CLOCK_TAI base > > time in update_vsyscall(). > > That’s... horrible. In an amazing way. Can you add BUILD_BUG_ON somewhere > to assert that this actually works? Sure, but changing any of the clock ids will cause more wreckage than that. Thanks, tglx___ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization
Re: [patch 11/11] x66/vdso: Add CLOCK_TAI support
> On Sep 14, 2018, at 5:50 AM, Thomas Gleixner wrote:
>
> With the storage array in place it's now trivial to support CLOCK_TAI in
> the vdso. Instead of extending the array to accomodate CLOCK_TAI, make use
> of the fact that:
>
> - CLOCK ids are set in stone
> - CLOCK_THREAD_CPUTIME is never going to be supported in the VDSO so
> the array slot 3 is unused
> - CLOCK_TAI is id 11 which results in 3 when masked with 0x3
>
> Add the mask to the basetime array lookup and set up the CLOCK_TAI base
> time in update_vsyscall().
That’s... horrible. In an amazing way. Can you add BUILD_BUG_ON somewhere to
assert that this actually works?
>
> The performance impact of the mask operation is within the noise.
>
> Signed-off-by: Thomas Gleixner
> ---
> arch/x86/entry/vdso/vclock_gettime.c|2 +-
> arch/x86/entry/vsyscall/vsyscall_gtod.c |4
> arch/x86/include/asm/vgtod.h|6 +-
> 3 files changed, 10 insertions(+), 2 deletions(-)
>
> --- a/arch/x86/entry/vdso/vclock_gettime.c
> +++ b/arch/x86/entry/vdso/vclock_gettime.c
> @@ -140,7 +140,7 @@ notrace static inline u64 vgetcyc(int mo
>
> notrace static int do_hres(clockid_t clk, struct timespec *ts)
> {
> -struct vgtod_ts *base = >basetime[clk];
> +struct vgtod_ts *base = >basetime[clk & VGTOD_HRES_MASK];
>u64 cycles, last, ns;
>unsigned int seq;
>
> --- a/arch/x86/entry/vsyscall/vsyscall_gtod.c
> +++ b/arch/x86/entry/vsyscall/vsyscall_gtod.c
> @@ -51,6 +51,10 @@ void update_vsyscall(struct timekeeper *
>base->sec = tk->xtime_sec;
>base->nsec = tk->tkr_mono.xtime_nsec;
>
> +base = >basetime[VGTOD_TAI];
> +base->sec = tk->xtime_sec + (s64)tk->tai_offset;
> +base->nsec = tk->tkr_mono.xtime_nsec;
> +
>base = >basetime[CLOCK_MONOTONIC];
>base->sec = tk->xtime_sec + tk->wall_to_monotonic.tv_sec;
>nsec = tk->tkr_mono.xtime_nsec;
> --- a/arch/x86/include/asm/vgtod.h
> +++ b/arch/x86/include/asm/vgtod.h
> @@ -19,9 +19,13 @@ struct vgtod_ts {
> };
>
> #define VGTOD_BASES(CLOCK_MONOTONIC_COARSE + 1)
> -#define VGTOD_HRES(BIT(CLOCK_REALTIME) | BIT(CLOCK_MONOTONIC))
> +#define VGTOD_HRES(BIT(CLOCK_REALTIME) | BIT(CLOCK_MONOTONIC) |
> BIT(CLOCK_TAI))
> #define VGTOD_COARSE(BIT(CLOCK_REALTIME_COARSE) |
> BIT(CLOCK_MONOTONIC_COARSE))
>
> +/* Abuse CLOCK_THREAD_CPUTIME_ID for VGTOD CLOCK TAI */
> +#define VGTOD_HRES_MASK0x3
> +#define VGTOD_TAI(CLOCK_TAI & VGTOD_HRES_MASK)
> +
> /*
> * vsyscall_gtod_data will be accessed by 32 and 64 bit code at the same time
> * so be carefull by modifying this structure.
>
>
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[patch 11/11] x66/vdso: Add CLOCK_TAI support
With the storage array in place it's now trivial to support CLOCK_TAI in
the vdso. Instead of extending the array to accomodate CLOCK_TAI, make use
of the fact that:
- CLOCK ids are set in stone
- CLOCK_THREAD_CPUTIME is never going to be supported in the VDSO so
the array slot 3 is unused
- CLOCK_TAI is id 11 which results in 3 when masked with 0x3
Add the mask to the basetime array lookup and set up the CLOCK_TAI base
time in update_vsyscall().
The performance impact of the mask operation is within the noise.
Signed-off-by: Thomas Gleixner
---
arch/x86/entry/vdso/vclock_gettime.c|2 +-
arch/x86/entry/vsyscall/vsyscall_gtod.c |4
arch/x86/include/asm/vgtod.h|6 +-
3 files changed, 10 insertions(+), 2 deletions(-)
--- a/arch/x86/entry/vdso/vclock_gettime.c
+++ b/arch/x86/entry/vdso/vclock_gettime.c
@@ -140,7 +140,7 @@ notrace static inline u64 vgetcyc(int mo
notrace static int do_hres(clockid_t clk, struct timespec *ts)
{
- struct vgtod_ts *base = >basetime[clk];
+ struct vgtod_ts *base = >basetime[clk & VGTOD_HRES_MASK];
u64 cycles, last, ns;
unsigned int seq;
--- a/arch/x86/entry/vsyscall/vsyscall_gtod.c
+++ b/arch/x86/entry/vsyscall/vsyscall_gtod.c
@@ -51,6 +51,10 @@ void update_vsyscall(struct timekeeper *
base->sec = tk->xtime_sec;
base->nsec = tk->tkr_mono.xtime_nsec;
+ base = >basetime[VGTOD_TAI];
+ base->sec = tk->xtime_sec + (s64)tk->tai_offset;
+ base->nsec = tk->tkr_mono.xtime_nsec;
+
base = >basetime[CLOCK_MONOTONIC];
base->sec = tk->xtime_sec + tk->wall_to_monotonic.tv_sec;
nsec = tk->tkr_mono.xtime_nsec;
--- a/arch/x86/include/asm/vgtod.h
+++ b/arch/x86/include/asm/vgtod.h
@@ -19,9 +19,13 @@ struct vgtod_ts {
};
#define VGTOD_BASES(CLOCK_MONOTONIC_COARSE + 1)
-#define VGTOD_HRES (BIT(CLOCK_REALTIME) | BIT(CLOCK_MONOTONIC))
+#define VGTOD_HRES (BIT(CLOCK_REALTIME) | BIT(CLOCK_MONOTONIC) |
BIT(CLOCK_TAI))
#define VGTOD_COARSE (BIT(CLOCK_REALTIME_COARSE) |
BIT(CLOCK_MONOTONIC_COARSE))
+/* Abuse CLOCK_THREAD_CPUTIME_ID for VGTOD CLOCK TAI */
+#define VGTOD_HRES_MASK0x3
+#define VGTOD_TAI (CLOCK_TAI & VGTOD_HRES_MASK)
+
/*
* vsyscall_gtod_data will be accessed by 32 and 64 bit code at the same time
* so be carefull by modifying this structure.
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