linux-kernel - Re: [PATCH 2/4] block: Implement a blk_yield function to voluntarily give up the I/O scheduler.

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Message-ID: <x49fx2wemwt.fsf@segfault.boston.devel.redhat.com>
Date:	Thu, 15 Apr 2010 11:49:22 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	Vivek Goyal <vgoyal@...hat.com>, linux-kernel@...r.kernel.org,
	linux-ext4@...r.kernel.org
Subject: Re: [PATCH 2/4] block: Implement a blk_yield function to voluntarily give up the I/O scheduler.

Jens Axboe <jens.axboe@...cle.com> writes:

> On Wed, Apr 14 2010, Vivek Goyal wrote:

>> > @@ -1887,6 +1891,9 @@ static void cfq_dispatch_insert(struct request_queue *q, struct request *rq)
>> >  
>> >  	cfqd->rq_in_flight[cfq_cfqq_sync(cfqq)]++;
>> >  	cfqq->nr_sectors += blk_rq_sectors(rq);
>> > +
>> > +	if (cfq_cfqq_yield(cfqq) && RB_EMPTY_ROOT(&cfqq->sort_list))
>> > +		cfq_yield_cfqq(cfqd, cfqq);
>> 
>> Jeff,
>> 
>> I am wondering if cfq_select_queue() will be a better place for yielding
>> the queue.
>> 
>> 	if (cfq_cfqq_yield(cfqq) && RB_EMPTY_ROOT(&cfqq->sort_list))
>> 			goto expire;
>> 
>> We can avoid one unnecessary __blk_run_queue().
>
> Agree, doing it on insert is not the right place.

I see where you're coming from, but that makes things quite a bit
trickier.  I look forward to the review of *that* patch.  ;-)

Cheers,
Jeff
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