kern/131360: [nfs] poor scaling behavior of the NFS server under
rwatson at FreeBSD.org
Sun Mar 1 11:10:03 PST 2009
The following reply was made to PR kern/131360; it has been noted by GNATS.
From: Robert Watson <rwatson at FreeBSD.org>
To: FreeBSD-gnats-submit at FreeBSD.org
Subject: Re: kern/131360: [nfs] poor scaling behavior of the NFS server under
Date: Sun, 1 Mar 2009 19:06:25 +0000 (GMT)
On Wed, 4 Feb 2009, Martin Birgmeier wrote:
> [Please note that the email address given is not valid due
> to security reasons. Just reply to the gnats entry, and
> I'll follow it via the web interface.]
> Between FreeBSD 6.3 and 7.1, the behavior of the NFS server
> changed for the worse. Under 6.3, the load generated by the
> nfsd's would never exceed their number (I am using
> nfs_server_flags="-u -t -n 8"). With 7.1, when the client
> generates a lot of requests, it seems that the load on the
> NFS server can grow nearly without bounds, rendering the
> server all but unusable.
Could I ask you to clarify a few things about the NFS server configuration:
- What device/device driver is on the server?
- Is the mount over TCP or UDP?
There are a number of changes between 7.0, one of the potential changes to
look at is the increased UDP parallelism support due to read-locking in the
UDP stack overwhelming the capabilities of some device/device drivers. We've
had a couple of reports of this specifically with the bge driver. If you're
using UDP, converting to TCP would be interesting; if it's bge, then we could
give you a patch to locally revert the read-locking changes to see if that
helps manage contention better (i.e., more contention higher on a sec of locks
moves the contention off the single device driver lock).
Robert N M Watson
University of Cambridge
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