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

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Message-ID: <CANejiEW46KSZHLqn5-ZLCpMV_MyQsJB2kghrvzcEpvigod+9zA@mail.gmail.com>
Date:	Tue, 14 Feb 2012 10:36:36 +0800
From:	Shaohua Li <shli@...nel.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	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,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] block: strip out locking optimization in put_io_context()

2012/2/14 Tejun Heo <tj@...nel.org>:
> Hello, Shaohua.
>
> Can you please test the following patch?  It's combination of three
> patches which invokes elevator icq exit from exit_io_context().  This
> unfortunately ends up adding another reverse locking loop and using
> RCU could be better; unfortunately, the change isn't trivial due to
> q->queue_lock modification during blk_cleanup_queue() and ioc cleanup
> being called after that from blk_release_queue() - IOW, while holding
> RCU, we might end up grabbing the wrong q lock (I don't think this is
> a new problem).
>
> Now that we have proper request draining on queue exit, we can
> probably move ioc clearing and other operations to blk_cleanup_queue()
> and then apply RCU, but that's for another merge window.
This fixed the regression. Thanks!
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