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From: Raghavendra D Prabhu <raghu.prabhu13@gmail.com>
To: Brian Candler <brian@soundmouse.com>
Cc: Christoph Hellwig <hch@infradead.org>, xfs@oss.sgi.com
Subject: Re: Performance problem - reads slower than writes
Date: Wed, 1 Feb 2012 06:20:57 +0530	[thread overview]
Message-ID: <20120201005057.GA44385@Xye> (raw)
In-Reply-To: <20120131215210.GB47420@soundmouse.com>


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Hi,


* On Tue, Jan 31, 2012 at 09:52:10PM +0000, Brian Candler <brian@soundmouse.com> wrote:
>On Tue, Jan 31, 2012 at 09:52:05AM -0500, Christoph Hellwig wrote:
>> You don't just read a single file at a time but multiple ones, don't
>> you?
>
>It's sequential at the moment, although I'll do further tests with the -c
>(concurrency) option to bonnie++
>
>> Try playing with the following tweaks to get larger I/O to the disk:
>>
>>  a) make sure you use the noop or deadline elevators
>>  b) increase /sys/block/sdX/queue/max_sectors_kb from its low default
>>  c) dramatically increase /sys/devices/virtual/bdi/<major>:<minor>/read_ahead_kb
>
>Thank you very much: I will do further tests with these.
>
>Is the read_ahead_kb knob aware of file boundaries? That is, is there any
>risk that if I set it too large it would read useless blocks past the end of
>the file?

     The read_ahead_kb knob is used the by memory subsystem 
     readahead code to set the initial readahead to scale from (it 
     uses a dynamic scaling window). It is set by default based on 
     device readahead value (probably obtained in a way similar to 
     hdparm -I). 
     
     Setting it higher will be beneficial for sequential workloads 
     and the risk you mentioned is not there since it file 
     boundary aware -- check 
     http://lxr.linux.no/linux+*/mm/readahead.c#L151 for more 
     details.
>
>Regards,
>
>Brian.
>
>_______________________________________________
>xfs mailing list
>xfs@oss.sgi.com
>http://oss.sgi.com/mailman/listinfo/xfs


Regards,
-- 
Raghavendra Prabhu
GPG Id : 0xD72BE977
Fingerprint: B93F EBCB 8E05 7039 CD3C A4B8 A616 DCA1 D72B E977
www: wnohang.net

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  reply	other threads:[~2012-02-01  0:51 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-01-30 22:00 Performance problem - reads slower than writes Brian Candler
2012-01-31  2:05 ` Dave Chinner
2012-01-31 10:31   ` Brian Candler
2012-01-31 14:16     ` Brian Candler
2012-01-31 20:25       ` Dave Chinner
2012-02-01  7:29         ` Stan Hoeppner
2012-02-03 18:47         ` Brian Candler
2012-02-03 19:03           ` Christoph Hellwig
2012-02-03 21:01             ` Brian Candler
2012-02-03 21:17               ` Brian Candler
2012-02-05 22:50                 ` Dave Chinner
2012-02-05 22:43               ` Dave Chinner
2012-01-31 14:52     ` Christoph Hellwig
2012-01-31 21:52       ` Brian Candler
2012-02-01  0:50         ` Raghavendra D Prabhu [this message]
2012-02-01  3:59         ` Dave Chinner
2012-02-03 11:54       ` Brian Candler
2012-02-03 19:42         ` Stan Hoeppner
2012-02-03 22:10           ` Brian Candler
2012-02-04  9:59             ` Stan Hoeppner
2012-02-04 11:24               ` Brian Candler
2012-02-04 12:49                 ` Stan Hoeppner
2012-02-04 20:04                   ` Brian Candler
2012-02-04 20:44                     ` Joe Landman
2012-02-06 10:40                       ` Brian Candler
2012-02-07 17:30                       ` Brian Candler
2012-02-05  5:16                     ` Stan Hoeppner
2012-02-05  9:05                       ` Brian Candler
2012-01-31 20:06     ` Dave Chinner
2012-01-31 21:35       ` Brian Candler

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