On Fri, Jan 25, 2013 at 03:35:21PM -0500, J. Bruce Fields wrote: > On Fri, Jan 25, 2013 at 03:21:07PM -0500, J. Bruce Fields wrote: > > > > > On Fri, Jan 25, 2013 at 01:29:35PM -0600, Ben Myers wrote: > > > > Hey Bruce & Jim & Olga, > > > > > > > > On Fri, Jan 25, 2013 at 02:16:20PM -0500, Jim Rees wrote: > > > > > J. Bruce Fields wrote: > > > > > > > > > > On Thu, Jan 24, 2013 at 06:59:30PM -0600, Ben Myers wrote: > > > > > > At 1020 threads the send buffer size wraps and becomes negative causing > > > > > > the nfs server to grind to a halt. Rather than setting bufsize based > > > > > > upon the number of nfsd threads, make the buffer sizes tuneable via > > > > > > module parameters. > > > > > > > > > > > > Set the buffer sizes in terms of the number of rpcs you want to fit into > > > > > > the buffer. > > > > > > > > > > From private communication, my understanding is that the original > > > > > problem here was due to memory pressure forcing the tcp send buffer size > > > > > below the size required to hold a single rpc. > > > > > > > > Years ago I did see wrapping of the buffer size when tcp was used with many > > > > threads. Today's problem is timeouts on a cluster with a heavy read > > > > workload... and I seem to remember seeing that the send buffer size was too > > > > small. > > > > > > > > > In which case the important variable here is lock_bufsize, as that's > > > > > what prevents the buffer size from going too low. > > > > > > > > I tested removing the lock of bufsize and did hit the timeouts, so the overflow > > > > is starting to look less relevant. I will test your minimal overflow fix to > > > > see if this is the case. > > > > > > The minimal overflow fix did not resolve the timeouts. > > > > OK, thanks, that's expected. > > > > > I will test with this to see if it resolves the timeouts: > > > > And I'd expect that to do the job--but at the expense of some tcp > > bandwidth. So you end up needing your other module parameters to get > > the performance back. > > Also, what do you see happening on the server in the problem case--are > threads blocking in svc_send, or are they dropping replies? Oh, never mind, right, it's almost certainly svc_tcp_has_wspace failing: required = atomic_read(&xprt->xpt_reserved) + serv->sv_max_mesg; if (sk_stream_wspace(svsk->sk_sk) >= required) return 1; set_bit(SOCK_NOSPACE, &svsk->sk_sock->flags); return 0; That returns 0 once sk_stream_wspace falls below sv_max_mesg, so we never take the request and don't get to the point of failing in svc_send. --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
