[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date: Mon, 7 Jul 2008 14:33:06 -0700
From: Stephen Hemminger <shemminger@...tta.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, 07 Jul 2008 17:30:49 -0400
Olga Kornievskaia <aglo@...i.umich.edu> wrote:
>
>
> Stephen Hemminger wrote:
> > On Mon, 07 Jul 2008 14:18:38 -0400
> > Olga Kornievskaia <aglo@...i.umich.edu> wrote:
> >
> >
> >> Hi,
> >>
> >> I'd like to ask a question regarding socket options, more
> >> specifically send and receive buffer sizes.
> >>
> >> One simple question: (on the server-side) is it true that, to set
> >> send/receive buffer size, setsockopt() can only be called before
> >> listen()? From what I can tell, if I were to set socket options for the
> >> listening socket, they get inherited by the socket created during the
> >> accept(). However, when I try to change send/receive buffer size for the
> >> new socket, they take no affect.
> >>
> >> The server in question is the NFSD server in the kernel. NFSD's code
> >> tries to adjust the buffer size (in order to have TCP increase the
> >> window size appropriately) but it does so after the new socket is
> >> created. It leads to the fact that the TCP window doesn't open beyond
> >> the TCP's "default" sysctl value (that would be the 2nd value in the
> >> triple net.ipv4.tcp_rmem, which on our system is set to 64KB). We
> >> changed the code so that setsockopt() is called for the listening socket
> >> is created and we set the buffer sizes to something bigger, like 8MB.
> >> Then we try to increase the buffer size for each socket created by the
> >> accept() but what is seen on the network trace is that window size
> >> doesn't open beyond the values used for the listening socket.
> >>
> >
> > It would be better if NFSD stayed out of doign setsockopt and just
> > let the sender/receiver autotuning work?
> >
> Auto-tuning would be guided by the sysctl values that are set for all
> applications. I could be wrong but what I see is that unless an
> application does a setsockopt(), its window is bound by the default
> sysctl value. If it is true, than it is not acceptable. It means that in
> order for NFSD to achieve a large enough window it needs to modify TCP's
> sysctl value which will effect all other applications.
>
Auto tuning starts at the default and will expand to the max allowed.
If you set a value with setsockopt, then the kernel just uses that value
and does no tuning.
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Powered by blists - more mailing lists