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From: Andy Lutomirski <luto@amacapital.net>
Date: Fri, 19 Dec 2014 09:42:36 -0800
Message-ID: <CALCETrWxziEYyGrujXWScAfNsw2nWGMVEPRK-ck2Rniktjhpfg@mail.gmail.com>
Subject: Re: [PATCH v2 3/3] X86: Add a thread cpu time implementation to vDSO
To: Peter Zijlstra <peterz@infradead.org>
Cc: Shaohua Li <shli@fb.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        X86 ML <x86@kernel.org>, Kernel-team@fb.com,
        "H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
        John Stultz <john.stultz@linaro.org>
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Sender: linux-kernel-owner@vger.kernel.org

On Fri, Dec 19, 2014 at 9:27 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> On Fri, Dec 19, 2014 at 09:07:49AM -0800, Andy Lutomirski wrote:
>> Re-asking my old question: would it make sense to add a vdso helper
>> for the magic self-monitoring interface?  Or, at the very least, we
>> could try to tidy up the docs a bit.
>
> I find it really helps (performance wise) to strip down that magic to
> the bare minimum required.
>
> A VDSO helper would always have to do everything.  I suppose we could
> provide a generic helper, one can always hand code the stuff anyhow.
>
> Then again, what is the benefit of having it in the VDSO as opposed to a
> regular DSO?

The benefit of using the VDSO is that it means that we can change the
data structure whenever we want.  The __vdso_clock_gettime data
structure changes on a somewhat regular basis.

Other than that, a regular DSO is somewhat easier.

>
> Updating the docs is always good.

:)

--Andy

-- 
Andy Lutomirski
AMA Capital Management, LLC
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