linux-kernel - Re: [PATCH] cfq-iosched: non-rot devices do not need read queue merging

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Date:	Tue, 05 Jan 2010 16:19:08 -0500
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Vivek Goyal <vgoyal@...hat.com>,
	Corrado Zoccolo <czoccolo@...il.com>
Cc:	Jens Axboe <jens.axboe@...cle.com>,
	Linux-Kernel <linux-kernel@...r.kernel.org>,
	Shaohua Li <shaohua.li@...el.com>,
	Gui Jianfeng <guijianfeng@...fujitsu.com>
Subject: Re: [PATCH] cfq-iosched: non-rot devices do not need read queue merging

Vivek Goyal <vgoyal@...hat.com> writes:

> Thanks Jeff, one thing comes to mind. Now with recent changes, we drive deeper
> depths on SSD with NCQ and there are not many pending cfqq on service tree
> until and unless number of parallel threads exceed NCQ depth (32). If
> that's the case, then I think we might not be seeing lot of queue merging
> happening in this test case until and unless dump utility is creating more
> than 32 threads.
>
> If time permits, it might also be interesting to run the same test with queue
> depth 1 and see if SSDs without NCQ will suffer or not.

Corrado, I think what Vivek is getting at is that you should check for
both blk_queue_nonrot and cfqd->hw_tag (like in cfq_arm_slice_timer).
Do you agree?

Cheers,
Jeff
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