linux-kernel - Re: filesystem benchmarking fun

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Date:	Wed, 16 May 2007 16:14:14 -0400
From:	Chris Mason <chris.mason@...cle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Chuck Ebbert <cebbert@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: filesystem benchmarking fun

On Wed, May 16, 2007 at 01:04:13PM -0700, Andrew Morton wrote:
> > The good news is that if you let it run long enough, the times
> > stabilize.  The bad news is:
> > 
> > create dir kernel-86 222MB in 15.85 seconds (14.03 MB/s)
> > create dir kernel-87 222MB in 28.67 seconds (7.76 MB/s)
> > create dir kernel-88 222MB in 18.12 seconds (12.27 MB/s)
> > create dir kernel-89 222MB in 19.77 seconds (11.25 MB/s)
> 
> well hang on.  Doesn't this just mean that the first few runs were writing
> into pagecache and the later ones were blocking due to dirty-memory limits?
> 
> Or do you have a sync in there?
> 
There's no sync,  but if you watch vmstat you can clearly see the log
flushes, even when the overall create times are 11MB/s.  vmstat goes
30MB/s -> 4MB/s or less, then back up to 30MB/s.

On the same box, my shiny new FS writes at 30MB/s the whole time.  For
this part of the benchmark, I think we should all be getting the same
numbers.

-chris

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