linux-kernel - Re: [patch]block: revert a patch

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Date:	Thu, 11 Aug 2011 10:39:48 +0200
From:	Jens Axboe <jaxboe@...ionio.com>
To:	Shaohua Li <shaohua.li@...el.com>
CC:	"boyu.mt@...bao.com" <boyu.mt@...bao.com>,
	Christoph Hellwig <hch@...radead.org>,
	"dan.j.williams@...el.com" <dan.j.williams@...el.com>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [patch]block: revert a patch

On 2011-08-11 09:11, Shaohua Li wrote:
> This patch reverts commit 35ae66e0a09ab70ed(block: Make rq_affinity = 1
> work as expected). The purpose is to avoid an unnecessary IPI.
> Let's take an example. My test box has cpu 0-7, one socket. Say request is
> added from CPU 1, blk_complete_request() occurs at CPU 7. Without the reverted
> patch, softirq will be done at CPU 7. With it, an IPI will be directed to CPU
> 0, and softirq will be done at CPU 0. In this case, doing softirq at CPU 0 and
> CPU 7 have no difference from cache sharing point view and we can avoid an
> ipi if doing it in CPU 7.
> An immediate concern is this is just like QUEUE_FLAG_SAME_FORCE, but actually
> not. blk_complete_request() is running in interrupt handler, and currently
> I/O controller doesn't support multiple interrupts (I checked several LSI
> cards and AHCI), so only one CPU can run blk_complete_request(). This is
> still quite different as QUEUE_FLAG_SAME_FORCE.
> Since only one CPU runs softirq, the only difference with below patch is
> softirq not always runs at the first CPU of a group.

Thanks, I applied this but fixed up your subject line. You can't just
call it 'revert a patch', does not carry a lot of meaning!

-- 
Jens Axboe

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