linux-kernel - Re: [PATCH 05/10] block: remove per-queue plugging

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Message-ID: <4D75F9B5.1050704@fusionio.com>
Date:	Tue, 8 Mar 2011 10:41:09 +0100
From:	Jens Axboe <jaxboe@...ionio.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Mike Snitzer <snitzer@...hat.com>, Shaohua Li <shli@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"hch@...radead.org" <hch@...radead.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH 05/10] block: remove per-queue plugging

On 2011-03-08 10:38, Peter Zijlstra wrote:
> On Mon, 2011-03-07 at 21:46 +0100, Jens Axboe wrote:
>>
>> Great, that'll work for me! Your patch should work as-is, then. Thanks
>> Peter.
> 
> Well I think it would be good to write it like:
> 
>   if (prev->state != TASK_RUNNING && blkneeds_flush(prev)) {
>     raw_spin_unlock(&rq->lock);
>     blk_flush_plug(prev);
>     raw_spin_lock(&rq->lock);
>   }
> 
> To avoid flipping that lock when we don't have to.

Yes good point, in any case the need to flush will be an unlikely event.
So saving the lock/unlock dance for when we really need it is a good
optimization.

-- 
Jens Axboe

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