linux-kernel - Re: [PATCH] perf: add 'perf bench syscall'

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Date:	Tue, 21 Jun 2016 09:55:39 -0500
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Rik van Riel <riel@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>, clark@...hat.com,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH] perf: add 'perf bench syscall'

On Mon, Jun 20, 2016 at 12:16:22PM -0700, Andy Lutomirski wrote:
> On Mon, Jun 20, 2016 at 11:00 AM, Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> 
> >
> > From: Josh Poimboeuf <jpoimboe@...hat.com>
> > Subject: [PATCH] perf: add 'perf bench syscall'
> >
> > Add a basic 'perf bench syscall' benchmark which does a getppid() system
> > call in a tight loop.
> >
> 
> My one suggestion would be to use a different syscall than getppid(),
> as getppid() can have unusual performance characteristics on kernels
> with pid namespaces enabled.  I'm a fan of prctl(-1, 0, 0, 0, 0).

Hm, can you elaborate on the unusual performance characteristics of
getppid()?  The code seems pretty minimal.

prctl() actually seems much worse to me, because of all the security
module cruft.

-- 
Josh