[Top] [All Lists]

Re: Performance problem - reads slower than writes

To: Brian Candler <brian@xxxxxxxxxxxxxx>
Subject: Re: Performance problem - reads slower than writes
From: Raghavendra D Prabhu <raghu.prabhu13@xxxxxxxxx>
Date: Wed, 1 Feb 2012 06:20:57 +0530
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
Dkim-signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=date:from:to:cc:subject:message-id:mail-followup-to:references :mime-version:content-type:content-disposition:in-reply-to :x-operating-system:x-editor:user-agent; bh=d9UC8/F9tUNHiMmPMTfNLpIVhFRQDobA/yKOsawlgNE=; b=iJCZdF+F0p0rmgQPgkH0P7Vorxt1Fnh8jXKrkNyMR23iGFOGK6NIPxdZ+HFOZBSRTf YeklbfRYmgtsT48eN30p7YB928WNng80nQQaWiI2PVhY3Asa/6eYdjakizcijgs6eEMX FxfkuxnB6OnTMDuLuPBJF2h+P/WM6xhGqDNO8=
In-reply-to: <20120131215210.GB47420@xxxxxxxxxxxxxx>
Mail-followup-to: Brian Candler <brian@xxxxxxxxxxxxxx>, Christoph Hellwig <hch@xxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
References: <20120130220019.GA45782@xxxxxxxx> <20120131020508.GF9090@dastard> <20120131103126.GA46170@xxxxxxxx> <20120131145205.GA6607@xxxxxxxxxxxxx> <20120131215210.GB47420@xxxxxxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-12-30)

* On Tue, Jan 31, 2012 at 09:52:10PM +0000, Brian Candler 
<brian@xxxxxxxxxxxxxx> 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

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.



xfs mailing list

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

Attachment: pgpoCP3RXuwA7.pgp
Description: PGP signature

<Prev in Thread] Current Thread [Next in Thread>