linux-kernel - Re: [patch]block: fix ioc locking warning

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Date:	Tue, 7 Feb 2012 08:31:22 +0800
From:	Shaohua Li <shaohua.li@...el.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Vivek Goyal <vgoyal@...hat.com>, Jens Axboe <axboe@...nel.dk>,
	lkml <linux-kernel@...r.kernel.org>,
	Knut Petersen <Knut_Petersen@...nline.de>, mroos@...ux.ee
Subject: Re: [patch]block: fix ioc locking warning

2012/2/7 Tejun Heo <tj@...nel.org>:
> On Mon, Feb 06, 2012 at 09:27:06AM -0800, Tejun Heo wrote:
>> It's one wq scheduling on exit for any task which has issued an IO.  I
>> don't think it would matter except for task fork/exit microbenchs (or
>> workloads which approximate to that).  I'll get some measurements and
>> strip the optimization if it doesn't really show up.
>
> I'm still playing with test methods and getting numbers but the
> following is the simplified one of the three setups I'm playing with -
> the current one, simplified and no optimization.  There *seems* to be
> appreciable performance degradation on fork/exit w/ ioc microbenchs so
> I'm likely to go with the following.  I'll post when I know more.
Hi,
Since you are talking about performance, one of our microbenchmark (swap)
shows a regression. Alex bisect it to be b2efa05265d62bc2, which is related to
the ioc change. A little strange to me, don't expect such change can cause
performance issue. I haven't double check the issue, but if you have
ideas, please
let me know.

Thanks,
Shaohua
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