linux-ext4 - Re: ext4 unlink performance

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Date:	Wed, 19 Nov 2008 16:18:40 -0500
From:	Theodore Tso <tytso@....edu>
To:	Andreas Dilger <adilger@....com>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: ext4 unlink performance

On Wed, Nov 19, 2008 at 12:10:01PM -0600, Andreas Dilger wrote:
> 
> That may be a side-effect of the mballoc per-CPU cache again, where
> files being written in the same subdirectory are spread apart because
> of the write thread being rescheduled to different cores.
> 

It would be good for us to get confirmation one way or another about
this theory.  Bruce, if you have multiple CPU's (or cores on your
system --- i.e., cat /proc/cpuinfo reports multiple processors), can
you try unpacking your tarball on a test ext4 filesystem using
something like:

    taskset 1 tar xjf /path/to/my/tarball.tar.bz2

The "taskset 1" will bind the tar process to only run on a single
processors.  If that significantly changes the time to do run rm -rf,
can you save a raw e2image using that workload?  That would be very
useful indeed.

Alternatively, if you don't have the taskset command handy, you can
also add maxcpus=1 to the kernel boot command-line, which will force
the system to only use one cpu.  Using taskset is much more
convenient, though.

Thanks!!

						- Ted
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