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Re: Performance problem - reads slower than writes

To: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Subject: Re: Performance problem - reads slower than writes
From: Brian Candler <brian@xxxxxxxxxxxxxx>
Date: Tue, 31 Jan 2012 21:52:10 +0000
Cc: Dave Chinner <david@xxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
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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?



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