On Tue, Jul 07, 2009 at 12:57:16PM +0200, Corinna Vinschen
wrote:> when trying to optimize socket transfer rates under Cygwin, it turned
> out that the underlying WinSock implementation is surprisingly sensitive
> to buffer sizes. The latest Cygwin from CVS is now setting the socket
> receive/send buffers (SO_RCVBUF/SO_SNDBUF) to 64K, rather than keeping
> them at their default values of 8K which thwarts data transfers a lot.
>
> While testing I still had the problem that for some reason the ssh read
> transfer rates were only a third up to a half of the write transfer
> rates. It turned out that the culprit was ssh itself. In clientloop.c,
> it defines read buffers of the size 8K. Setting them to 64K under
> Cygwin raises the read transfer rates comparable to the write rates.
>
> It occured to me that we talked about this already 3 years ago in a
> thread about HPN-SSH, just the performance numbers were different:
> http://marc.info/?l=openssh-unix-dev&m=114414372902485&w=2
>
> So the question I have is again this:
>
> Would it be ok to raise the buffers in client_process_net_input() and
> client_process_input() to 64K, maybe only on Cygwin? Or to make the
> buffer sizes a configurable option?
If there's a measureable performance gain (which it sounds like there is)
then I personally have no objection to making it a compile time option.
Damien? Maybe something like this?
Index: clientloop.c
==================================================================RCS file:
/home/dtucker/openssh/cvs/openssh/clientloop.c,v
retrieving revision 1.201
diff -u -p -r1.201 clientloop.c
--- clientloop.c 5 Jul 2009 21:17:35 -0000 1.201
+++ clientloop.c 7 Jul 2009 11:38:33 -0000
@@ -636,7 +636,7 @@ static void
client_process_net_input(fd_set *readset)
{
int len, cont = 0;
- char buf[8192];
+ char buf[SSH_IOBUFSZ];
/*
* Read input from the server, and add any such data to the buffer of
@@ -1129,7 +1129,7 @@ static void
client_process_input(fd_set *readset)
{
int len;
- char buf[8192];
+ char buf[SSH_IOBUFSZ];
/* Read input from stdin. */
if (FD_ISSET(fileno(stdin), readset)) {
Index: configure.ac
==================================================================RCS file:
/home/dtucker/openssh/cvs/openssh/configure.ac,v
retrieving revision 1.420
diff -u -p -r1.420 configure.ac
--- configure.ac 16 Jun 2009 06:11:02 -0000 1.420
+++ configure.ac 7 Jul 2009 11:41:04 -0000
@@ -442,6 +442,7 @@ int main(void) { exit(0); }
AC_DEFINE(DISABLE_FD_PASSING, 1,
[Define if your platform needs to skip post auth
file descriptor passing])
+ AC_DEFINE(SSH_IOBUFSZ, 65536, [Windows is sensitive to read buffer size])
;;
*-*-dgux*)
AC_DEFINE(IP_TOS_IS_BROKEN, 1,
Index: defines.h
==================================================================RCS file:
/home/dtucker/openssh/cvs/openssh/defines.h,v
retrieving revision 1.155
diff -u -p -r1.155 defines.h
--- defines.h 16 Jun 2009 06:11:02 -0000 1.155
+++ defines.h 7 Jul 2009 11:39:15 -0000
@@ -749,4 +749,8 @@ struct winsize {
#define INET6_ADDRSTRLEN 46
#endif
+#ifndef SSH_IOBUFSZ
+# define SSH_IOBUFSZ 8192
+#endif
+
#endif /* _DEFINES_H */
--
Darren Tucker (dtucker at zip.com.au)
GPG key 8FF4FA69 / D9A3 86E9 7EEE AF4B B2D4 37C9 C982 80C7 8FF4 FA69
Good judgement comes with experience. Unfortunately, the experience
usually comes from bad judgement.