Trond Myklebust <trond.myklebust@xxxxxxxxxx> writes: > On Thu, 2009-05-14 at 09:34 -0400, Jeff Moyer wrote: >> Trond Myklebust <trond.myklebust@xxxxxxxxxx> writes: >> >> > On Wed, 2009-05-13 at 15:29 -0400, Jeff Moyer wrote: >> >> Hi, netdev folks. The summary here is: >> >> >> >> A patch added in the 2.6.30 development cycle caused a performance >> >> regression in my NFS iozone testing. The patch in question is the >> >> following: >> >> >> >> commit 47a14ef1af48c696b214ac168f056ddc79793d0e >> >> Author: Olga Kornievskaia <aglo@xxxxxxxxxxxxxx> >> >> Date: Tue Oct 21 14:13:47 2008 -0400 >> >> >> >> svcrpc: take advantage of tcp autotuning >> >> >> >> which is also quoted below. Using 8 nfsd threads, a single client doing >> >> 2GB of streaming read I/O goes from 107590 KB/s under 2.6.29 to 65558 >> >> KB/s under 2.6.30-rc4. I also see more run to run variation under >> >> 2.6.30-rc4 using the deadline I/O scheduler on the server. That >> >> variation disappears (as does the performance regression) when reverting >> >> the above commit. >> > >> > It looks to me as if we've got a bug in the svc_tcp_has_wspace() helper >> > function. I can see no reason why we should stop processing new incoming >> > RPC requests just because the send buffer happens to be 2/3 full. If we >> > see that we have space for another reply, then we should just go for it. >> > OTOH, we do want to ensure that the SOCK_NOSPACE flag remains set, so >> > that the TCP layer knows that we're congested, and that we'd like it to >> > increase the send window size, please. >> > >> > Could you therefore please see if the following (untested) patch helps? >> >> I'm seeing slightly better results with the patch: >> >> 71548 >> 75987 >> 71557 >> 87432 >> 83538 >> >> But that's still not up to the speeds we saw under 2.6.29. The packet >> capture for one run can be found here: >> http://people.redhat.com/jmoyer/trond.pcap.bz2 >> >> Cheers, >> Jeff > > Yes. Something is very wrong there... > > See for instance frame 1195, where the client finishes sending a whole > series of READ requests, and we go into a flurry of ACKs passing > backwards and forwards, but no data. It looks as if the NFS server isn't > processing anything, probably because the window size falls afoul of the > svc_tcp_has_wspace()... > > Does something like this help? Sorry for the previous, stupid question. I applied the patch in addition the last one and here are the results: 70327 71561 68760 69199 65324 A packet capture for this run is available here: http://people.redhat.com/jmoyer/trond2.pcap.bz2 Any more ideas? ;) -Jeff -- 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
