On Wed, Oct 31, 2012 at 08:46:58PM -0200, Marcelo Tosatti wrote:
> Originally from Jeremy Fitzhardinge.
>
> pvclock_get_time_values, which contains the memory barriers
> will be removed by next patch.
>
> Signed-off-by: Marcelo Tosatti <[email protected]>
>
> Index: vsyscall/arch/x86/kernel/pvclock.c
> ===================================================================
> --- vsyscall.orig/arch/x86/kernel/pvclock.c
> +++ vsyscall/arch/x86/kernel/pvclock.c
> @@ -97,10 +97,10 @@ cycle_t pvclock_clocksource_read(struct
>
> do {
> version = pvclock_get_time_values(&shadow, src);
> - barrier();
> + rdtsc_barrier();
> offset = pvclock_get_nsec_offset(&shadow);
> ret = shadow.system_timestamp + offset;
> - barrier();
> + rdtsc_barrier();
> } while (version != src->version);
>
> if ((valid_flags & PVCLOCK_TSC_STABLE_BIT) &&
>
On a guest without SSE2 rdtsc_barrier() will be nop while rmb() will
be "lock; addl $0,0(%%esp)". I doubt pvclock will work correctly either
way though.
--
Gleb.
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