linux-kernel - Re: [PATCH] perf tools: Dont use openat()

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Date:	Sat, 26 Sep 2009 17:01:03 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Ulrich Drepper <drepper@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Fr??d??ric Weisbecker <fweisbec@...il.com>,
	linux kernel <linux-kernel@...r.kernel.org>,
	linux-perf-users@...r.kernel.org
Subject: Re: [PATCH] perf tools: Dont use openat()


* Eric Dumazet <eric.dumazet@...il.com> wrote:

> Ulrich Drepper a ??crit :
> > -----BEGIN PGP SIGNED MESSAGE-----
> > Hash: SHA1
> > 
> > Eric Dumazet wrote:
> >>> We can certainly remove that reliance - wanna send a patch for it?
> > 
> > Come on, the silliness has to stop.  The kernel must be recent and to
> > use it adequately the C library also must be recent.  And "recent" is
> > not even correct anymore: the functions are available for more then two
> > years.  Removing the use of the modern interfaces makes everything
> > slower and might even re-introduce race conditions my patch fixed.
> > 
> 
> First time I ear that C library *must* be recent. This was never
> mentionned in Documentation/Changes, "Minimal Requirements"
> 
> "perf list" can be 100x slower, and even racy, I dont mind. At all.
> 
> $ time perf list >/dev/null 2>/dev/null
> 
> real    0m0.001s
> user    0m0.000s
> sys     0m0.001s

Yep, doesnt look problematic from a performance POV.

> With openat(), I cannot use "perf" on machines I can only change 
> kernel, since changing glibc is too risky for legacy apps. I could use 
> static and private glibc, but last time I tried this I lost few hours 
> and failed.

Yeah, we generally dont want to force an upgrade of other components if 
possible. The fact that you ran into it in a pre -rc1 kernel means that 
there's a thousand others out there who will run into similar problems.

	Ingo
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