linux-kernel - Re: [PATCH] block: strip out locking optimization in put_io

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Date:	Wed, 8 Feb 2012 16:29:53 +0800
From:	Shaohua Li <shaohua.li@...el.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jens Axboe <axboe@...nel.dk>, Vivek Goyal <vgoyal@...hat.com>,
	lkml <linux-kernel@...r.kernel.org>,
	Knut Petersen <Knut_Petersen@...nline.de>, mroos@...ux.ee
Subject: Re: [PATCH] block: strip out locking optimization in put_io_context()

2012/2/8 Shaohua Li <shaohua.li@...el.com>:
> 2012/2/8 Tejun Heo <tj@...nel.org>:
>> Hello,
>>
>> On Tue, Feb 07, 2012 at 08:33:15AM -0800, Linus Torvalds wrote:
>>> Yeah, please just get rid of the crazy code. Maybe *that* fixes the
>>> regression too, who knows?
>>>
>>> For all we know, the "fast case" is what causes extra locking only to
>>> then fail and not even be a fast-path.
>>
>> Yeah, I was about to ask Shaohua to test the version w/o optimization.
>> With heavily loaded request_queue, trylock failure could be frequent,
>> which I wasn't testing.
>>
>> Shaohua, can you please test the version w/o optimization?  Also, can
>> you please give a bit more details on the setup?  Are there multiple
>> swap devices?  Is it SSD or rotating disk?
> the test adds mem=4G in a 2 sockets 16 CPU machine.
> just make several copy of kernel source in tmpfs (so there is swap
> depending on your
> memory size) and run kernel build in the kernel source in the meaning time.
> there is only one swap device which is a rotating disk.
>
> I'll test both patches soon.
Tried all the options, the regression still exists. Any new idea?
I'll spend some time on it if I can get anything

Thanks,
Shaohua
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