From: William Lee Irwin III <wli@holomorphy.com>
To: Andrew Morton <akpm@osdl.org>
Cc: Con Kolivas <kernel@kolivas.org>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] Instrumenting high latency
Date: Mon, 12 Jul 2004 01:02:59 -0700 [thread overview]
Message-ID: <20040712080259.GV21066@holomorphy.com> (raw)
In-Reply-To: <20040712003418.02997a12.akpm@osdl.org>
On Mon, Jul 12, 2004 at 12:34:18AM -0700, Andrew Morton wrote:
> OK, small problem. We have code which does, effectively,
> if (need_resched()) {
> drop_the_lock();
> schedule();
> grab_the_lock();
> }
> so if need_resched() stays false then this will hold the lock for a long
> time and bogus reports are generated:
> 46ms non-preemptible critical section violated 1 ms preempt threshold starting at exit_mmap+0x26/0x188 and ending at exit_mmap+0x154/0x188
> To fix that you need to generate high scheduling pressure so that
> need_resched() is frequently true. On all CPUs. Modify realfeel to pin
> itself to each CPU, or something like that.
I suspect it's better to drop in hooks to trap those e.g. in
cond_resched() and cond_resched_lock().
On Mon, Jul 12, 2004 at 12:34:18AM -0700, Andrew Morton wrote:
> This rather decreases the patch's usefulness.
> The way I normally do this stuff is with
> http://www.zip.com.au/~akpm/linux/patches/stuff/rtc-debug.patch
> and `amlat', from http://www.zip.com.au/~akpm/linux/amlat.tar.gz
> It _might_ be sufficient to redefine need_resched() to just return 1 all
> the time. If that causes the kernel to livelock then we need to fix that
> up anyway.
Less code... not sure how nasty performance the implications are.
-- wli
next prev parent reply other threads:[~2004-07-12 8:03 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-07-12 6:29 Con Kolivas
2004-07-12 6:37 ` Andrew Morton
2004-07-12 6:43 ` Con Kolivas
2004-07-12 6:58 ` Andrew Morton
2004-07-12 7:00 ` [PATCH] " William Lee Irwin III
2004-07-12 7:34 ` Andrew Morton
2004-07-12 8:02 ` William Lee Irwin III [this message]
2004-07-12 8:38 ` William Lee Irwin III
2004-07-12 11:31 ` William Lee Irwin III
2004-07-12 14:32 ` William Lee Irwin III
2004-07-12 17:09 ` Martin Josefsson
2004-07-12 8:29 ` Arjan van de Ven
2004-07-12 8:42 ` William Lee Irwin III
2004-07-12 8:47 ` William Lee Irwin III
2004-07-12 10:41 ` Rajput
2004-07-12 10:44 ` William Lee Irwin III
2004-07-12 14:24 ` Martin J. Bligh
2004-07-12 14:27 ` Con Kolivas
2004-07-12 14:33 ` Martin J. Bligh
2004-07-12 14:42 ` Con Kolivas
2004-07-12 14:47 ` Martin J. Bligh
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