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? Cheers Trond --------------------------------------------------------------------- >From 85e3f5860a9063d193bdb45516b3d3d347b87301 Mon Sep 17 00:00:00 2001 From: Trond Myklebust <Trond.Myklebust@xxxxxxxxxx> Date: Thu, 14 May 2009 10:33:07 -0400 Subject: [PATCH] SUNRPC: Always allow the NFS server to process at least one request Signed-off-by: Trond Myklebust <Trond.Myklebust@xxxxxxxxxx> --- net/sunrpc/svcsock.c | 9 ++++++++- 1 files changed, 8 insertions(+), 1 deletions(-) diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c index 8962355..4837442 100644 --- a/net/sunrpc/svcsock.c +++ b/net/sunrpc/svcsock.c @@ -972,9 +972,16 @@ static int svc_tcp_has_wspace(struct svc_xprt *xprt) { struct svc_sock *svsk = container_of(xprt, struct svc_sock, sk_xprt); struct svc_serv *serv = svsk->sk_xprt.xpt_server; + int reserved; int required; - required = (atomic_read(&xprt->xpt_reserved) + serv->sv_max_mesg) * 2; + reserved = atomic_read(&xprt->xpt_reserved); + /* Always allow the server to process at least one request, whether + * or not the TCP window is large enough + */ + if (reserved == 0) + return 1; + required = (reserved + serv->sv_max_mesg) << 1; if (sk_stream_wspace(svsk->sk_sk) < required) goto out_nospace; return 1; -- 1.6.0.4 -- 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
