Date: Mon, 3 Jun 2013 15:37:58 -0400
To: jens kusch <jens.kusch@oracle.com>
Cc: linux-nfs@vger.kernel.org
Subject: Re: strange nfsd scheduling in 2.6.32
Message-ID: <20130603193758.GB2109@fieldses.org>
References: <51A8B08C.3090309@oracle.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
In-Reply-To: <51A8B08C.3090309@oracle.com>
From: "J. Bruce Fields" <bfields@fieldses.org>
Sender: linux-nfs-owner@vger.kernel.org

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
> --
> To unsubscribe from this list: send the line "unsubscribe linux-nfs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html