linux-kernel - Re: cfq-iosched: tiobench regression

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Date:	Thu, 24 Dec 2009 12:40:39 +0100
From:	Corrado Zoccolo <czoccolo@...il.com>
To:	Shaohua Li <shaohua.li@...el.com>,
	Gui Jianfeng <guijianfeng@...fujitsu.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"jens.axboe@...cle.com" <jens.axboe@...cle.com>,
	"jmoyer@...hat.com" <jmoyer@...hat.com>,
	"Zhang, Yanmin" <yanmin.zhang@...el.com>
Subject: Re: cfq-iosched: tiobench regression

The default setting should satisfy most users (how many desktop users
run 32 concurrent seq.readers?).
Those who have particular needs (e.g. DB users) can try their workload
with both settings. low latency can probably benefit them too, if the
workload is latency sensitive.

Corrado

2009/12/24, Shaohua Li <shaohua.li@...el.com>:
> On Thu, Dec 24, 2009 at 03:48:38PM +0800, Gui Jianfeng wrote:
>> Shaohua Li wrote:
>> > We see about 30% regression in tiobench 32 threads 80M file sequential
>> > read.
>> > The regression is caused by below commits.
>> >
>> > 5db5d64277bf390056b1a87d0bb288c8b8553f96
>> > The commit makes the slice too small. In the test, the slice is limitted
>> > to 2 * idle_slice(300ms/32 < 2*idle_slice). This dramatically impacts io
>> > thoughput. The low_latency knob used to be only impact random io, now it
>> > impacts sequential io too. Any idea to fix it?
>>
>> Hi Shaohua,
>>
>> IMHO this shouldn't be a problem. Currently, low_latency is used to
>> improve
>> the latency for the whole system. If someone would like to achieve high
>> throughput,
>> just turn off low_latency knob.
> The concern is low_latency is default on. A end user is unlikely to know the
> knob.
>
> Thanks,
> Shaohua
>

-- 
Inviato dal mio dispositivo mobile

__________________________________________________________________________

dott. Corrado Zoccolo                          mailto:czoccolo@...il.com
PhD - Department of Computer Science - University of Pisa, Italy
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