From: Andi Kleen <andi@firstfloor.org>
To: Ingo Molnar <mingo@elte.hu>
Cc: Hitoshi Mitake <mitake@dcl.info.waseda.ac.jp>,
andi@firstfloor.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH][RFC] Adding information of counts processes acquired how many spinlocks to schedstat II
Date: Wed, 1 Jul 2009 15:50:34 +0200 [thread overview]
Message-ID: <20090701135034.GU6760@one.firstfloor.org> (raw)
In-Reply-To: <20090701090749.GA13535@elte.hu>
On Wed, Jul 01, 2009 at 11:07:49AM +0200, Ingo Molnar wrote:
> His arguments are bogus: both lockstat and perfcounters are optional
> (and default off), and the sw counter can be made near zero cost
> even if both perfcounters and lockstat is enabled. Also, sw counters
> are generally per CPU, etc. so not a performance issue.
BTW I looked through the code generated by this again. As far as I
can see it still uses a global flag word to enable/disable the counter.
The standard problem -- discussed a lot -- with that set up used to be that
if the kernel is entered cache cold then you end up with a potential full cache
miss (200-1000 cycles) just to access that global variable. The old LTT
had a neat optimization to patch in immediate values to avoid this problem.
Has this been considered for these counters? With such a change
it might be indeed a "small" cost even in the worst cases.
-Andi
--
ak@linux.intel.com -- Speaking for myself only.
next prev parent reply other threads:[~2009-07-01 13:50 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-07-01 6:21 [PATCH][RFC] Adding information of counts processes acquired how many spinlocks to schedstat Hitoshi Mitake
2009-07-01 7:31 ` Ingo Molnar
2009-07-01 8:21 ` Hitoshi Mitake
2009-07-01 13:45 ` Frederic Weisbecker
2009-07-01 13:50 ` Ingo Molnar
2009-07-01 14:17 ` mitake
2009-07-01 7:38 ` Andi Kleen
2009-07-01 8:42 ` Hitoshi Mitake
2009-07-01 9:07 ` Ingo Molnar
2009-07-01 9:42 ` Hitoshi Mitake
2009-07-01 11:06 ` Ingo Molnar
2009-07-01 12:53 ` Hitoshi Mitake
2009-07-01 15:44 ` Frederic Weisbecker
2009-07-06 5:20 ` mitake
2009-07-06 8:51 ` Peter Zijlstra
2009-07-06 11:54 ` Andi Kleen
2009-07-10 12:45 ` mitake
2009-07-10 12:52 ` Peter Zijlstra
2009-07-10 13:43 ` Ingo Molnar
2009-07-10 13:46 ` Frederic Weisbecker
2009-07-10 13:50 ` Ingo Molnar
2009-07-10 13:56 ` Peter Zijlstra
2009-07-12 7:23 ` Hitoshi Mitake
2009-07-12 13:24 ` Peter Zijlstra
2009-07-13 6:06 ` Hitoshi Mitake
2009-07-13 8:51 ` Ingo Molnar
2009-07-14 0:48 ` Hitoshi Mitake
2009-07-18 13:25 ` Ingo Molnar
2009-07-01 12:40 ` Andi Kleen
2009-07-01 13:50 ` Andi Kleen [this message]
2009-07-01 9:48 ` Andi Kleen
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