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From: Roberto Spadim <roberto@spadim.com.br>
To: Shaohua Li <shli@kernel.org>
Cc: linux-raid@vger.kernel.org, neilb@suse.de, axboe@kernel.dk
Subject: Re: [patch 2/3 v3] raid1: read balance chooses idlest disk for SSD
Date: Mon, 2 Jul 2012 01:36:53 -0300	[thread overview]
Message-ID: <CABYL=Tp745DWrzC=ZixVvEa4CHANP8ozpcc_E7Amy+m3HkcO3A@mail.gmail.com> (raw)
In-Reply-To: <CABYL=Tresfnb+9369_Y4_PrF0-RY3FjgRZ6e_N8d5iPrTRVr-Q@mail.gmail.com>

sorry about many posts, i will stop a bit now...

could we turn off disk NCQ? ok nobody want to read this, but could we
turn off NCQ and get better performace? since we do a good elevator at
linux code... maybe turn off disk cache too... (it´s only 32MB for
sata/sas, and can be alot to raid controller...), just some ideas to
get better performace... (i didn´t think before write if cache help or
not when we send I/O to disk, but check if it´s a good question or
not)

2012/7/2 Roberto Spadim <roberto@spadim.com.br>:
> for SSD without inteligent parts (cache and queue) i think this could
> works nice... (at least in theory)
> for USB sticks and microsd cards may work too...
>
>
> 2012/7/2 Shaohua Li <shli@kernel.org>:
>> On Sun, Jul 01, 2012 at 11:13:42PM -0300, Roberto Spadim wrote:
>>> nice =) very very nice =)
>>> maybe to get better than this... select the disk with min(pending time)
>>>
>>> time could be estimated with something like:
>>> (distance * time/distance unit) + (blocks to read/write * time to
>>> read/write 1 block) + (non sequencial penalty time)
>>
>> I didn't think there is way to measure request time. Disks support NCQ, they
>> can dispatch several requests at one time and finish them almost at the same
>> time. I used to measure this time (to make CFQ ioscheduler self tune), but
>> failed.
>>
>> Thanks,
>> Shaohua
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
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>
>
>
> --
> Roberto Spadim
> Spadim Technology / SPAEmpresarial



-- 
Roberto Spadim
Spadim Technology / SPAEmpresarial
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  reply	other threads:[~2012-07-02  4:36 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-07-02  1:08 [patch 0/3 v3] Optimize raid1 read balance for SSD Shaohua Li
2012-07-02  1:08 ` [patch 1/3 v3] raid1: make sequential read detection per disk based Shaohua Li
2012-07-04  5:38   ` NeilBrown
2012-07-02  1:08 ` [patch 2/3 v3] raid1: read balance chooses idlest disk for SSD Shaohua Li
2012-07-02  2:13   ` Roberto Spadim
2012-07-02  3:02     ` Shaohua Li
2012-07-02  3:57       ` Roberto Spadim
2012-07-02  4:33         ` Roberto Spadim
2012-07-02  4:31       ` Roberto Spadim
2012-07-02  4:36         ` Roberto Spadim [this message]
2012-07-04  5:45   ` NeilBrown
2012-07-02  1:08 ` [patch 3/3 v3] raid1: prevent merging too large request Shaohua Li
2012-07-04  5:59   ` NeilBrown
2012-07-04  8:01     ` Shaohua Li

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