linux-kernel - Re: [PATCH]block: make auto block plug flush threshold per-disk based

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Date:	Mon, 09 Apr 2012 10:13:12 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Jens Axboe <axboe@...nel.dk>
Cc:	Shaohua Li <shli@...nel.org>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH]block: make auto block plug flush threshold per-disk based

Jens Axboe <axboe@...nel.dk> writes:

> On 2012-04-06 11:27, Shaohua Li wrote:
>> We do auto block plug flush to reduce latency, the threshold is 16
>> requests. This works well if the task is accessing one or two drives.
>> The problem is if the task is accessing a raid 0 device and the raid
>> disk number is big, say 8 or 16, 16/8 = 2 or 16/16=1, we will have
>> heavy lock contention.
>> 
>> This patch makes the threshold per-disk based. The latency should be
>> still ok accessing one or two drives. The setup with application
>> accessing a lot of drives in the meantime uaually is big machine,
>> avoiding lock contention is more important, because any contention
>> will actually increase latency.
>
> Thanks, applied. It should have been per-queue all along, so this
> makes a lot of sense.

Yeah, I had noticed this before when looking over the code.  Makes
sense.

Acked-by: Jeff Moyer <jmoyer@...hat.com>
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