netdev - Re: setsockopt()

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Date:	Mon, 7 Jul 2008 18:17:08 -0700
From:	"John Heffner" <johnwheffner@...il.com>
To:	"Olga Kornievskaia" <aglo@...i.umich.edu>
Cc:	netdev@...r.kernel.org, "Jim Rees" <rees@...ch.edu>,
	"J. Bruce Fields" <bfields@...ldses.org>
Subject: Re: setsockopt()

On Mon, Jul 7, 2008 at 11:18 AM, Olga Kornievskaia <aglo@...i.umich.edu> wrote:
>   Can somebody advise us on how to properly set send/receive buffer sizes
> for the NFSD in the kernel such that (1) the window is not bound by the
> TCP's default sysctl value and (2) if it is possible to do so for the accept
> sockets and not the listening socket.

As others have said, most likely you'd be better off without calling
SO_{SND,RCV}BUF.  It's possible but difficult in some circumstances to
do better than the kernel's autotuning.

If you must do SO_RCVBUF, you also need to set TCP_WINDOW_CLAMP.  It
would probably be better if the kernel would recalculate window_clamp
on an SO_RCVBUF automatically, though this is slightly problematic
from a layering point of view.  Note, however, that changing SO_RCVBUF
after connection establishment is not supported on many OS's, and
usually isn't what you want to do.

  -John
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