linux-kernel - Re: [PATCH v2 3/3] X86: Add a thread cpu time implementation to vDSO

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

On Fri, Dec 19, 2014 at 9:27 AM, Peter Zijlstra <peterz@...radead.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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