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Subject: Re: AIM7 40% regression with 2.6.26-rc1
From: "Zhang, Yanmin" <yanmin_zhang@linux.intel.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Ingo Molnar <mingo@elte.hu>, Matthew Wilcox <matthew@wil.cx>,
       LKML <linux-kernel@vger.kernel.org>,
       Alexander Viro <viro@ftp.linux.org.uk>,
       Linus Torvalds <torvalds@linux-foundation.org>
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Date: Wed, 07 May 2008 12:46:16 +0800
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On Tue, 2008-05-06 at 20:59 -0700, Andrew Morton wrote:
> On Wed, 07 May 2008 11:41:52 +0800 "Zhang, Yanmin" <yanmin_zhang@linux.intel.com> wrote:
> 
> > As system idle is more than 50%, so the schedule/schedule_timeout caller is important
> > information.
> > 1) lock_kernel causes most schedule/schedule_timeout;
> > 2) When lock_kernel calls down, then __down, __down calls ___schedule_timeout for
> > lots of times in a loop;
> 
> Really?  Are you sure?  That would imply that we keep on waking up tasks
> which then fail to acquire the lock.  But the code pretty plainly doesn't
> do that.
Yes, totally based on the data.
The data means the calling times among functions. Initially , I just collected the caller
of schedule and schedule_timeout. Then I found most schedule/schedule_timeout are called by
__down which is called down. Then, I changes kernel to collect more functions' calling info.

If comparing the calling times of down, __down and schedule_timeout, we could find
schedule_timeout is called by __down for 222330308, but __down is called only for 153190.

> 
> Odd.
> 
> > 3) Caller of lcok_kernel are sys_fcntl/vfs_ioctl/tty_release/chrdev_open.
> Still :(
Yes. The data has an error difference, but the difference is small. My patch doesn't
use lock to protect data in case it might introduces too much overhead.