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List:       fuse-devel
Subject:    Re: [fuse-devel] fuse stat performance on multicore systems
From:       Stefan Westerfeld <stefan () space ! twc ! de>
Date:       2012-06-20 10:09:52
Message-ID: 20120620100952.GB7140 () space ! twc ! de
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   Hi!

On Wed, Jun 13, 2012 at 12:21:09PM -0300, Han-Wen Nienhuys wrote:
> On Wed, Jun 13, 2012 at 11:52 AM, Stefan Westerfeld <stefan@space.twc.de> wrote:
> 
> > So it seems that FuSE becomes really slow for stat/readdir when more than
> > one CPU is available (probably because the userspace client and filesystem
> > work ends up being done on different CPUs).
> 
> You should probably verify this theory first? You can instrument the
> library to measure how much time it spends to answer stat calls.

Ok, I'll try to gather more data by instrumenting libfuse. I'll be on vacation
for three weeks now, and won't have access to a multicore machine there. So I
will collect more data when I'm back, and mail it to the list.

> FUSE creates a thread per request, reusing threads if possible.
> Another possible slowdown is that the FUSE threads run on different
> CPUs and contend for shared locks to inspect the in-process inode
> tree.

I don't believe that can be the cause, because if there is a single userspace
process that does stat/readdir calls, then only one FuSE thread should be
active, as there is at most one open FuSE request to process at any given time.

   Cu... Stefan
-- 
Stefan Westerfeld, Hamburg/Germany, http://space.twc.de/~stefan

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