Re: Window sizes.

From: Chris Hellberg (odysseus@soa.co.nz)
Date: Mon Jul 22 2002 - 14:41:39 EST


On Mon, Jul 22, 2002 at 04:34:30PM +0200, Rogier Wolff wrote:
>
> Hi,
>
> 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
> second.
>
> 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.....

Never having done this before, my best guess would be to change
the following line in the kernel source and recompile:

include/net/tcp.h:#define MAX_TCP_WINDOW 32767U

You've got the scaling going, but of source it's scaling right
up to your maximum window size.

Chris
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