From: Tao Ma <tm@tao.ma>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: linux-kernel@vger.kernel.org, Jens Axboe <axboe@kernel.dk>
Subject: Re: [PATCH] block: Make cfq_target_latency tunable through sysfs.
Date: Thu, 29 Mar 2012 08:36:37 +0800 [thread overview]
Message-ID: <4F73AE95.1060402@tao.ma> (raw)
In-Reply-To: <20120329003228.GA18424@kroah.com>
On 03/29/2012 08:32 AM, Greg KH wrote:
> On Tue, Mar 27, 2012 at 04:16:53PM +0800, Tao Ma wrote:
>> From: Tao Ma <boyu.mt@taobao.com>
>>
>> In cfq, when we calculate a time slice for a process(or a cfqq to
>> be precise), we have to consider the cfq_target_latency so that all the
>> sync request have an estimated latency(300ms) and it is controlled by
>> cfq_target_latency. But in some hadoop test, we have found that if
>> there are many processes doing sequential read(24 for example), the
>> throughput is bad because every process can only work for about 25ms
>> and the cfqq is switched. That leads to a higher disk seek. We can
>> achive the good throughput by setting low_latency=0, but then some
>> read's latency is too much for the application.
>>
>> So this patch makes cfq_target_latency tunable through sysfs so that
>> we can tune it and find some magic number which is not bad for both
>> the throughput and the read latency.
>
> If you add/modify sysfs files, you HAVE to also have a matching change
> to Documentation/ABI.
OK, I will add it in the next round. Great thanks.
Tao
>
> Please do so.
>
> thanks,
>
> greg k-h
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next prev parent reply other threads:[~2012-03-29 0:36 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-03-27 8:16 Tao Ma
2012-03-29 0:32 ` Greg KH
2012-03-29 0:36 ` Tao Ma [this message]
2012-03-29 10:38 ` Jens Axboe
2012-03-31 15:31 ` [PATCH V2 1/2] " Tao Ma
2012-03-31 15:31 ` [PATCH V2 2/2] Documentation: Add sysfs ABI change for cfq's target latency Tao Ma
2012-04-01 21:33 ` [PATCH V2 1/2] block: Make cfq_target_latency tunable through sysfs Jens Axboe
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