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List:       fuse-devel
Subject:    Re: [fuse-devel] stat performance on multicore systems: measurements
From:       Han-Wen Nienhuys <hanwenn () gmail ! com>
Date:       2012-07-25 20:02:18
Message-ID: CAOw_e7aLFVJy6zY7fE6YNMAicNF6FwdCzg1cH29mogDzxNkN2A () mail ! gmail ! com
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On Wed, Jul 25, 2012 at 10:48 AM, Stefan Westerfeld <stefan@space.twc.de> wrote:
>    Hi!
>
> On Wed, Jul 25, 2012 at 10:24:04AM -0700, Han-Wen Nienhuys wrote:
>> On Wed, Jul 25, 2012 at 9:12 AM, Stefan Westerfeld <stefan@space.twc.de> wrote:
>>
>> >> Similar results here:
>> >>
>> >> [...]
>> >>
>> >> Implementing this in FUSE seems like a worthwhile optimization point.
>> >
>> > Ok, I'll try to create a patch against FUSE to get this speedup.
>> >
>>
>> What will happen if the FS is accessed from multiple processes running
>> on different CPUs?
>
> The way I think it should work is that the FUSE fs will have different worker
> threads which are bound to one cpu per thread. If two processes running on cpu
> 1 and 3 access the filesystem, FUSE should use a worker thread bound to cpu 1
> to process requests from the userspace process running on cpu 1 and another
> worker thread bound to cpu 3 to process requests from the userspace process
> running on cpu 3.

This will perform poorly: the fuse library has a critical section
protected by mutexes, which are taken for each request. (see
fuse_loop_mt.c). If you make those run on different cpus, you will
have cache line bouncing for each request.

> Of course in this case the filesystem worker threads will not fully reside on
> the same cpu as the userspace processes, so it may not perform as good as in
> the case I measured with my test.
>
>    Cu... Stefan
> --
> Stefan Westerfeld, Hamburg/Germany, http://space.twc.de/~stefan



-- 
Han-Wen Nienhuys - hanwen@xs4all.nl - http://www.xs4all.nl/~hanwen

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