[Qemu-devel] TCP_NODELAY for -redir

[Daniel Jacobowitz]

I was trying to run GDB remote debug tests through a -redir socket
today.  It crawled unbelievably.  Paul guessed that slirp wasn't using
TCP_NODELAY, and Nagle was to blame.

He was even righter than usual.  Adding TCP_NODELAY speeds up this
particular workload by (very approximately) 54x.  See trivial attached
patch.

Is this going to bite other things, i.e. does it need to be
configurable?

-- 
Daniel Jacobowitz
CodeSourcery

---
 slirp/tcp.h      |    2 +-
 slirp/tcp_subr.c |    2 ++
 2 files changed, 3 insertions(+), 1 deletion(-)

Index: qemu/slirp/tcp.h
===================================================================
--- qemu.orig/slirp/tcp.h       2006-11-13 14:25:24.000000000 -0500
+++ qemu/slirp/tcp.h    2006-11-13 14:25:29.000000000 -0500
@@ -112,7 +112,7 @@ struct tcphdr {
 /*
  * User-settable options (used with setsockopt).
  */
-/* #define     TCP_NODELAY     0x01 */ /* don't delay send to coalesce packets 
*/
+#define        TCP_NODELAY     0x01    /* don't delay send to coalesce packets 
*/
 /* #define     TCP_MAXSEG      0x02 */ /* set maximum segment size */
 
 /*
Index: qemu/slirp/tcp_subr.c
===================================================================
--- qemu.orig/slirp/tcp_subr.c  2006-11-13 14:22:34.000000000 -0500
+++ qemu/slirp/tcp_subr.c       2006-11-13 14:23:31.000000000 -0500
@@ -499,6 +499,8 @@ tcp_connect(inso)
        setsockopt(s,SOL_SOCKET,SO_REUSEADDR,(char *)&opt,sizeof(int));
        opt = 1;
        setsockopt(s,SOL_SOCKET,SO_OOBINLINE,(char *)&opt,sizeof(int));
+       opt = 1;
+       setsockopt(s,IPPROTO_TCP,TCP_NODELAY,(char *)&opt,sizeof(int));
        
        so->so_fport = addr.sin_port;
        so->so_faddr = addr.sin_addr;