From: Gleb Natapov <gleb@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: kvm@vger.kernel.org
Subject: Re: [PATCH kvm-unit-tests] pmu: fixes for Sandy Bridge hosts
Date: Mon, 3 Jun 2013 09:38:54 +0300 [thread overview]
Message-ID: <20130603063854.GU4725@redhat.com> (raw)
In-Reply-To: <51AC38A9.5010703@redhat.com>
On Mon, Jun 03, 2013 at 08:33:13AM +0200, Paolo Bonzini wrote:
> Il 02/06/2013 17:32, Gleb Natapov ha scritto:
> > On Thu, May 30, 2013 at 07:43:07PM +0200, Paolo Bonzini wrote:
> >> This patch includes two fixes for SB:
> >>
> >> * the 3rd fixed counter ("ref cpu cycles") can sometimes report
> >> less than the number of iterations
> >>
> > Is it documented? It is strange for "architectural" counter to behave
> > differently on different architectures.
>
> It just counts the CPU cycles. If the CPU can optimize the loop better,
> it will take less CPU cycles to execute it.
>
We should try and change the loop so that it will not be so easily optimized.
Making the test succeed if only 10% percent of cycles were spend on a loop
may result in the test missing the case when counter counts something
different.
--
Gleb.
next prev parent reply other threads:[~2013-06-03 6:38 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-05-30 17:43 [PATCH kvm-unit-tests] pmu: fixes for Sandy Bridge hosts Paolo Bonzini
2013-05-30 17:43 ` [PATCH] " Paolo Bonzini
2013-05-30 17:45 ` Paolo Bonzini
2013-06-02 15:32 ` [PATCH kvm-unit-tests] " Gleb Natapov
2013-06-03 6:33 ` Paolo Bonzini
2013-06-03 6:38 ` Gleb Natapov [this message]
2013-06-03 7:08 ` Paolo Bonzini
2013-06-03 7:38 ` Gleb Natapov
2013-06-03 7:44 ` Paolo Bonzini
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