Re: autotuning of send buffer size of a socket

["Shirish Pargaonkar" <shirishpargaonkar@gmail.com>]

On 5/12/08, Sridhar Samudrala <sri@us.ibm.com> wrote:
> On Mon, 2008-05-12 at 14:00 -0500, Shirish Pargaonkar wrote:
> > Hello,
> >
> > kernel_sendmsg fails with error EAGAIN, yet I no matter how long I try,
> > I still get the same error and do not see the send buffer size of a socket
> > changing (increasing)
> >
> > The initial buffer sizes are 16384 for send side and 87380 for the receive
> > side but I see receive side buffer tuning but do not see the same with
> > send side.
> >
> > If tcp does not see a need to increase the send buffer size, wonder why I
> > get EAGAIN error on this non-blocking socket for kernel_sendmsg!
>
> I think the send buffer auto-tuning doesn't happen here because there is
> already congestion window worth of packets sent that are not yet acknowledged.
> See tcp_should_expand_sndbuf().

Sridhar,

The unacked (packets_out) is 7 and snd_cwnd is 9, so that should not be
the case for tcp_should_expand_sndbuf to return 0 right?

>
> Also, the comments for tcp_new_space() says that sndbuf expansion does
> not work well with largesends. What is the size of your sends?
>
> Adding netdev to the CC list.
>
> Thanks
> Sridhar
>
> >
> > I do subscribe to this mailing list so, please send your responses to this
> > mail address.
> >
> > Regards,
> >
> > Shirish
> >
> > --------------------------------------------------------------------------------------------------
> > uname -r
> > 2.6.18-91.el5
> >
> >  sysctl -a
> >
> > net.ipv4.tcp_rmem = 4096        87380   4194304
> > net.ipv4.tcp_wmem = 4096        16384   4194304
> > net.ipv4.tcp_mem = 98304        131072  196608
> >
> > net.core.rmem_default = 126976
> > net.core.wmem_default = 126976
> > net.core.rmem_max = 131071
> > net.core.wmem_max = 131071
> >
> > net.ipv4.tcp_window_scaling = 1
> > net.ipv4.tcp_timestamps = 1
> > net.ipv4.tcp_moderate_rcvbuf = 1
> >
> >
> > cat /proc/sys/net/ipv4/tcp_moderate_rcvbuf
> > 1
> >
> >
> > CIFS VFS: sndbuf 16384 rcvbuf 87380
> >
> > CIFS VFS: sends on sock 0000000009903100, sendbuf 34776, rcvbuf 190080
> > stuck for 32 seconds,
> > error: -11
> > CIFS VFS: sends on sock 0000000009903a00, sndbuf 34776, rcvbuf 138240
> > stuck for 32 seconds,
> > error: -11
> >
> >
> > CIFS VFS: sends on sock 0000000009903100, sndbuf 34776, rcvbuf 126720
> > stuck for 64 seconds,
> > error: -11
> >
> > CIFS VFS: sends on sock 0000000009903100, sndbuf 34776, rcvbuf 222720
> > stuck for 256 seconds,
> > error: -11
> >
> > I see the socket receive buffer size fluctuating (tcp_moderate_rcvbuf
> > is 1) but not
> > the socket send buffer size.
> > The send buffer size remains fixed, the auto-tuning for send side is
> > enabled by default,so I do not see it happening here no matter how
> > long the c ode tries to
> > kernel_sendmsg after receiving EAGAIN return code.
> > --
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>