From: Jens Axboe <jens.axboe@oracle.com>
To: Shaohua Li <shaohua.li@intel.com>
Cc: linux-kernel@vger.kernel.org, czoccolo@gmail.com,
vgoyal@redhat.com, jmoyer@redhat.com, guijianfeng@cn.fujitsu.com
Subject: Re: [PATCH] cfq-iosched: quantum check tweak --resend
Date: Mon, 1 Mar 2010 09:02:34 +0100 [thread overview]
Message-ID: <20100301080233.GO5768@kernel.dk> (raw)
In-Reply-To: <20100301015047.GA16630@sli10-desk.sh.intel.com>
On Mon, Mar 01 2010, Shaohua Li wrote:
> Currently a queue can only dispatch up to 4 requests if there are other queues.
> This isn't optimal, device can handle more requests, for example, AHCI can
> handle 31 requests. I can understand the limit is for fairness, but we could
> do a tweak: if the queue still has a lot of slice left, sounds we could
> ignore the limit. Test shows this boost my workload (two thread randread of
> a SSD) from 78m/s to 100m/s.
> Thanks for suggestions from Corrado and Vivek for the patch.
As mentioned before, I think we definitely want to ensure that we drive
the full queue depth whenever possible. I think your patch is a bit
dangerous, though. The problematic workload here is a buffered write,
interleaved with the occasional sync reader. If the sync reader has to
endure 32 requests every time, latency rises dramatically for him.
--
Jens Axboe
next prev parent reply other threads:[~2010-03-01 8:02 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-03-01 1:50 [PATCH] cfq-iosched: quantum check tweak --resend Shaohua Li
2010-03-01 8:02 ` Jens Axboe [this message]
2010-03-01 8:15 ` Shaohua Li
2010-03-01 8:19 ` Jens Axboe
2010-03-01 8:22 ` Shaohua Li
2010-03-01 8:25 ` Jens Axboe
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