* x86: kvmclock: drop rdtsc_barrier()
@ 2015-04-25 1:36 Marcelo Tosatti
2015-04-25 1:45 ` Rik van Riel
2015-04-29 1:47 ` Marcelo Tosatti
0 siblings, 2 replies; 3+ messages in thread
From: Marcelo Tosatti @ 2015-04-25 1:36 UTC (permalink / raw)
To: kvm; +Cc: Andy Lutomirski, Rik van Riel
Drop unnecessary rdtsc_barrier(), as has been determined empirically,
see 057e6a8c660e95c3f4e7162e00e2fee1fc90c50d for details.
Noticed by Andy Lutomirski.
Improves clock_gettime() by approximately 15% on
Intel i7-3520M @ 2.90GHz.
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
diff --git a/arch/x86/include/asm/pvclock.h b/arch/x86/include/asm/pvclock.h
index 25b1cc0..a5beb23 100644
--- a/arch/x86/include/asm/pvclock.h
+++ b/arch/x86/include/asm/pvclock.h
@@ -86,7 +86,6 @@ unsigned __pvclock_read_cycles(const struct pvclock_vcpu_time_info *src,
offset = pvclock_get_nsec_offset(src);
ret = src->system_time + offset;
ret_flags = src->flags;
- rdtsc_barrier();
*cycles = ret;
*flags = ret_flags;
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: x86: kvmclock: drop rdtsc_barrier()
2015-04-25 1:36 x86: kvmclock: drop rdtsc_barrier() Marcelo Tosatti
@ 2015-04-25 1:45 ` Rik van Riel
2015-04-29 1:47 ` Marcelo Tosatti
1 sibling, 0 replies; 3+ messages in thread
From: Rik van Riel @ 2015-04-25 1:45 UTC (permalink / raw)
To: Marcelo Tosatti, kvm; +Cc: Andy Lutomirski
On 04/24/2015 09:36 PM, Marcelo Tosatti wrote:
>
> Drop unnecessary rdtsc_barrier(), as has been determined empirically,
> see 057e6a8c660e95c3f4e7162e00e2fee1fc90c50d for details.
>
> Noticed by Andy Lutomirski.
>
> Improves clock_gettime() by approximately 15% on
> Intel i7-3520M @ 2.90GHz.
>
> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Acked-by: Rik van Riel <riel@redhat.com>
--
All rights reversed
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: x86: kvmclock: drop rdtsc_barrier()
2015-04-25 1:36 x86: kvmclock: drop rdtsc_barrier() Marcelo Tosatti
2015-04-25 1:45 ` Rik van Riel
@ 2015-04-29 1:47 ` Marcelo Tosatti
1 sibling, 0 replies; 3+ messages in thread
From: Marcelo Tosatti @ 2015-04-29 1:47 UTC (permalink / raw)
To: kvm; +Cc: Andy Lutomirski, Rik van Riel
On Fri, Apr 24, 2015 at 10:36:14PM -0300, Marcelo Tosatti wrote:
>
> Drop unnecessary rdtsc_barrier(), as has been determined empirically,
> see 057e6a8c660e95c3f4e7162e00e2fee1fc90c50d for details.
>
> Noticed by Andy Lutomirski.
>
> Improves clock_gettime() by approximately 15% on
> Intel i7-3520M @ 2.90GHz.
>
> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
>
> diff --git a/arch/x86/include/asm/pvclock.h b/arch/x86/include/asm/pvclock.h
> index 25b1cc0..a5beb23 100644
> --- a/arch/x86/include/asm/pvclock.h
> +++ b/arch/x86/include/asm/pvclock.h
> @@ -86,7 +86,6 @@ unsigned __pvclock_read_cycles(const struct pvclock_vcpu_time_info *src,
> offset = pvclock_get_nsec_offset(src);
> ret = src->system_time + offset;
> ret_flags = src->flags;
> - rdtsc_barrier();
>
> *cycles = ret;
> *flags = ret_flags;
>
> --
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