From: Marcelo Tosatti <mtosatti@redhat.com>
To: kvm@vger.kernel.org
Cc: Andy Lutomirski <luto@amacapital.net>, Rik van Riel <riel@redhat.com>
Subject: Re: x86: kvmclock: drop rdtsc_barrier()
Date: Tue, 28 Apr 2015 22:47:38 -0300 [thread overview]
Message-ID: <20150429014737.GA14997@amt.cnet> (raw)
In-Reply-To: <20150425013614.GA12023@amt.cnet>
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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Ping?
prev parent reply other threads:[~2015-04-29 1:47 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
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 [this message]
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