On Thu, Feb 19, 2009 at 05:42:49PM +1100, Greg Banks wrote: > J. Bruce Fields wrote: > > On Tue, Jan 13, 2009 at 09:26:36PM +1100, Greg Banks wrote: > > > >> Add /proc/fs/nfsd/pool_stats to export to userspace various > >> statistics about the operation of rpc server thread pools. > >> > > > > Could you explainw hy these specific statistics (total packets, > > sockets_queued, threads_woken, overloads_avoided, threads_timedout) are > > the important ones to capture? Could you give examples of what sort of > > problems could be solved using them? > > > Actually I originally added these stats to help debug the > overload-avoiding patch. Then I thought to use them to drive a > userspace control loop for controlling the number of nfsds, which I > never finished writing. > > As you said, an important question for the sysadmin is "should I > > configure more nfsds?" How do they answer that? > > > You can work that out, but it's not obvious, i.e. not human-friendly. > Firstly, you need to rate convert all the stats. > > The total_packets stat tells you how many NFS packets are arriving on > each thread pool. This is your primary load metric, i.e. with more load > you want more nfsd threads. > > The sockets_queued stat tells you that calls are arriving which are not > being immediately serviced by threads, i.e. you're either thread-limited > or CPU-limited rather than network-limited and you might get better > throughput if there were more nfsd threads. > > Conversely the overloads_avoided stat tells you if there are more > threads than can usefully be made runnable on the available CPUs, so > that adding more nfsd threads is unlikely to be helpful. > > The threads_timedout stat will give you a first-level approximation of > whether there are threads that are completely idle, i.e. don't see any > calls for the svc_recv() timeout (which I reduced to IIRC 10 sec as part > of the original version of this patch). This is a clue that you can now > reduce the number of threads. OK, thanks, that makes sense, but: it would be really fantastic if we could update and/or replace some of the howto's and faq's that are out there. The above would be useful, as would be some of the material from your nfs-tuning presentation. Queued up this and the old-stats removal for 2.6.30. --b. -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
