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From: Paolo Bonzini <pbonzini@redhat.com>
To: Jintack Lim <jintack@cs.columbia.edu>, kvm@vger.kernel.org
Cc: Christoffer Dall <christofferdall@gmail.com>,
	Shih-Wei Li <shihwei@cs.columbia.edu>
Subject: Re: rdtsc() in kvm-unit-tests on x86
Date: Mon, 10 Aug 2015 11:02:16 +0200	[thread overview]
Message-ID: <55C86898.3000003@redhat.com> (raw)
In-Reply-To: <CAHyh4xjBcSRZSkWpAT6whpxnNhrr8K4Y-Z23aw2P0Q2nx=ySOQ@mail.gmail.com>



On 07/08/2015 21:19, Jintack Lim wrote:
> Hi all,
> 
> While I was looking at rdtsc() code in kvm-unit-tests (e.g. x86/vmexit.c),
> I was getting curious that out-of-order execution on the processor
> may make rdtsc() executed not in the place we expect.
> 
> Referring to this document from intel,
> http://www.intel.com/content/www/us/en/embedded/training/ia-32-ia-64-benchmark-code-execution-paper.html
> they suggested to use rdtscp instruction and other techniques to
> serialize reading tsc register.
> 
> I wonder how the serialization is achieved when using rdtsc() in
> kvm-unit-tests code.
> Or, maybe the serialization is not necessary for some reason?

kvm-unit-tests executes the instruction thousands of times, so any error
due to lack of serialization is lost in the noise.

Paolo

  reply	other threads:[~2015-08-10  9:02 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-08-07 19:19 rdtsc() in kvm-unit-tests on x86 Jintack Lim
2015-08-10  9:02 ` Paolo Bonzini [this message]
     [not found]   ` <CAEDV+g+hwvSqWUjNAKcJVcTf-6vXx5j+YiN=aaYKJbo=pmWcEw@mail.gmail.com>
2015-08-10 13:58     ` Paolo Bonzini
2015-08-10 14:14       ` Jintack Lim
2015-08-10 14:47         ` Paolo Bonzini
2015-08-10 15:38           ` Jintack Lim

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