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

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Message-ID: <4F7F2A3D.3010700@kernel.dk>
Date:	Fri, 06 Apr 2012 11:39:09 -0600
From:	Jens Axboe <axboe@...nel.dk>
To:	Shaohua Li <shli@...nel.org>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH]block: make auto block plug flush threshold per-disk based

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.

-- 
Jens Axboe

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