(no subject)

[Ben Myers]

Bcc: 
Subject: Re: sunrpc: socket buffer size tuneable
Reply-To: 
In-Reply-To: <20130125192935.GA32470@sgi.com>

Hey, 

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.  I will test with this
to see if it resolves the timeouts:

---
 net/sunrpc/svcsock.c |    7 +++++++
 1 file changed, 7 insertions(+)

Index: b/net/sunrpc/svcsock.c
===================================================================
--- a/net/sunrpc/svcsock.c	2013-01-25 13:48:05.000000000 -0600
+++ b/net/sunrpc/svcsock.c	2013-01-25 13:49:42.000000000 -0600
@@ -435,6 +435,13 @@ static void svc_sock_setbufsize(struct s
 	lock_sock(sock->sk);
 	sock->sk->sk_sndbuf = snd * 2;
 	sock->sk->sk_rcvbuf = rcv * 2;
+
+	/*
+	 * The socket buffer can be resized by the networking code
+	 * unless you specify that this is not to be done.
+	 */
+	sock->sk->sk_userlocks |= SOCK_SNDBUF_LOCK|SOCK_RCVBUF_LOCK;
+
 	sock->sk->sk_write_space(sock->sk);
 	release_sock(sock->sk);
 #endif

Thanks,
Ben