Window sizes.

From: Rogier Wolff (
Date: Mon Jul 22 2002 - 09:34:30 EST


I'm trying to get some performance out of some gigabit ethernet
cards. Tweaking here and there we're now up to over 50 mbyte per

However, I think there is "more to be had": we're not close to the
wire speed, and both machines still have CPU free. (not only measured
through top and friends, but also measured with a concurrently running
"bogomips counter" (Attached below).)

The important settings we've changed to get to this point are:

tcp_mem:1048576 1048576 1048576
tcp_rmem:131072 131072 131072
tcp_wmem:131072 131072 131072

and the MTU for the link to 6000 (that's max for one of the cards that
we have)

but I still see only 32k of advertized "window". And at those speeds,
the window can easily be "too small". We would therefore like the window
to be advertized a bit larger.....


is already set at 1. What else do we need to change to get the
advertized window size to go up?



#include <stdio.h>
#include <signal.h>
#include <unistd.h>

volatile int count;

void alrm (int sig)
  static int oldcount=0;

  if (sig) {
    printf ("%d\n", count-oldcount);
    oldcount = count;
  signal (SIGALRM, alrm);
  alarm (1);

int main (int argc, char **argv)
  alrm (0);

  while (1)
    count ++;

** ** ** +31-15-2137555 **
*-- BitWizard writes Linux device drivers for any device you may have! --*
* There are old pilots, and there are bold pilots. 
* There are also old, bald pilots. 
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This archive was generated by hypermail 2b29 : Tue Jul 23 2002 - 22:00:02 EST