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Re: Poor performance using discard

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: Poor performance using discard
From: Thomas Lynema <lyz27@xxxxxxxxx>
Date: Fri, 02 Mar 2012 10:11:28 -0500
Cc: xfs@xxxxxxxxxxx
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In-reply-to: <20120229040819.GZ3592@dastard>
References: <1330469778.9688.7.camel@core24> <20120229012259.GW3592@dastard> <1330480826.9688.23.camel@core24> <20120229040819.GZ3592@dastard>
[....]

> Any errors in dmesg?

None

> 
> Also, I think you need to provide a block trace (output of
> blktrace/blkparse for the rm -rf workloads) for both the XFS and
> ext4 cases so we can see what discards are actually being issued and
> how long they take to complete....

Here's the output from running similar
commands as Christoph:

blkparse xfs.trace.blktrace.* | grep -w D | wc -l 
1134996
blkparse ext4.trace.blktrace.* | grep -w D | wc -l 
27240

Attached archives of most of the ext4 results. 
> 
> Cheers,
> 
> Dave.


Peter was right then.  Per multiple recommendations
I'm switching to fstrim, it is quicker than the deletes.

time fstrim -v /usr
/usr: 9047117824 bytes were trimmed

real    0m56.121s
user    0m0.110s
sys     0m0.000s

The subsequent runs consistently takes about a minute to run on a 40GB
volume.

time fstrim -v /usr
/usr: 9047117824 bytes were trimmed

real    0m56.121s
user    0m0.090s
sys     0m0.000s

I see that the running of fstrim was already discussed
http://oss.sgi.com/archives/xfs/2011-05/msg00338.html.

Please add something to the FAQ about using SSDs.  It would be great if
people could see the recommended mount options and fstrim crontab entry
(or other option) for running xfs on a SSD.  

Thanks for the input and patience.  

~tom




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