From: "J. Bruce Fields" <bfields@fieldses.org>
To: jens kusch <jens.kusch@oracle.com>
Cc: linux-nfs@vger.kernel.org
Subject: Re: strange nfsd scheduling in 2.6.32
Date: Mon, 3 Jun 2013 15:37:58 -0400 [thread overview]
Message-ID: <20130603193758.GB2109@fieldses.org> (raw)
In-Reply-To: <51A8B08C.3090309@oracle.com>
On Fri, May 31, 2013 at 04:15:40PM +0200, jens kusch wrote:
> Hi all,
>
> we have a problem with nfsd performance in 2.6.32. They don't seem
> to able to cope with the load. This is different in 2.6.18. Anybody
> seen this before?
>
> On Linux 2.6.32:
>
> - IOs are often processed by nfsd processes in a delayed fashion, as
> if they have been queued before (seen from application traces).
> - NFS pool statistics show only a smaller fraction processed
> immediately (10..20%). The rest is queued or delayed.
> - On the other hand there are lots of nfsd processes that sit idle
> at the same time!
> - CPU usage is very unevenly distributed among the nfsd servers,
> many are never used
>
> I'd just like to emphasize one detail: note the output from
> /proc/fs/nfsd/pool_stats below:
>
> # pool packets-arrived sockets-enqueued threads-woken
> overloads-avoided threads-timedout
> 0 7740103 1837083 885771 1837081 480
>
> The stat overloads-avoided always gets incremented in our runs. Here
> is a brief description:
The patch that added the "overload-avoidance" thing didn't work in
practice, and I couldn't figure out what it was meant to do, so it got
revoked with
78c210efdefe07131f91ed512a3308b15bb14e2f Revert "knfsd: avoid
overloading the CPU scheduler with enormous load averages"
Does appling that revoke help?
--b.
>
> Counts how many times the sunrpc server layer chose not to wake an
> nfsd thread, despite the presence of idle nfsd threads, because too
> many nfsd threads had been recently woken but could not get enough
> CPU time to actually run. In our runs, CPU utilization never gets
> close to 100%, so I wonder why NFS decided not to wake up one of the
> idle threads we see.
>
> In our runs, CPU utilization never gets close to 100%, so I wonder
> why NFS decided not to wake up one of the idle threads we see.
>
>
> On Linux 2.6.18
>
> - Performance via NFS is better
> - CPU usage is more evenly distributed among the nfsd processes, all
> nfsd processes are really used
>
> We would appreciate any hint about what could be wrong in 2.6.32.
>
> Best regards,
> Jens
> --
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next prev parent reply other threads:[~2013-06-03 19:37 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-05-31 14:15 strange nfsd scheduling in 2.6.32 jens kusch
2013-06-03 19:37 ` J. Bruce Fields [this message]
2013-06-04 16:16 ` jens kusch
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