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Message-Id: <1210873215.22262.14.camel@w-sridhar2.beaverton.ibm.com>
Date: Thu, 15 May 2008 10:40:15 -0700
From: Sridhar Samudrala <sri@...ibm.com>
To: Shirish Pargaonkar <shirishpargaonkar@...il.com>
Cc: linux-net@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: autotuning of send buffer size of a socket
On Thu, 2008-05-15 at 10:00 -0500, Shirish Pargaonkar wrote:
> On 5/14/08, Shirish Pargaonkar <shirishpargaonkar@...il.com> wrote:
> > On 5/12/08, Sridhar Samudrala <sri@...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?
It looks like sndbuf expansion via tcp_should_expand_sndbuf() happens
only in response to acks/data from the receiver.
tcp_rcv_established/tcp_rcv_state_process
tcp_data_snd_check
tcp_check_space
tcp_new_space
tcp_should_expand_sndbuf
auto-tuning doesn't increase sndbuf when trying to send more data.
> >
> > >
> > > 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.
> > > > --
> > > > To unsubscribe from this list: send the line "unsubscribe linux-net" in
> > > > the body of a message to majordomo@...r.kernel.org
> > > > More majordomo info at http://vger.kernel.org/majordomo-info.html
> > >
> > >
> >
>
> I put some printk in tcp.c (in function tcp_sendmsg)
> sndbuf grows from 16384 to 34776 but never beyond it.
>
>
> CIFS VFS: sndbuf 16384 rcvbuf 87380 rcvtimeo 0x7fffffffffffffff
>
> !sk_stream_memory_free queued 18288, sndbuf 16384
> sk_stream_wait_memory with 0 returned -11
> !sk_stream_memory_free queued 28448, sndbuf 27048
> sk_stream_wait_memory with 0 returned -11
> !sk_stream_memory_free queued 28448, sndbuf 27048
> sk_stream_wait_memory with 0 returned -11
> !sk_stream_memory_free queued 32512, sndbuf 30912
> sk_stream_wait_memory with 0 returned -11
> !sk_stream_memory_free queued 32512, sndbuf 30912
> sk_stream_wait_memory with 0 returned -11
> !sk_stream_memory_free queued 32512, sndbuf 30912
> sk_stream_wait_memory with 0 returned -11
> !sk_stream_memory_free queued 32512, sndbuf 30912
> sk_stream_wait_memory with 0 returned -11
> !sk_stream_memory_free queued 32512, sndbuf 30912
> sk_stream_wait_memory with 0 returned -11
> !sk_stream_memory_free queued 32512, sndbuf 30912
> sk_stream_wait_memory with 0 returned -11
> !sk_stream_memory_free queued 32512, sndbuf 30912
> sk_stream_wait_memory with 0 returned -11
> !sk_stream_memory_free queued 32512, sndbuf 30912
> sk_stream_wait_memory with 0 returned -11
> !sk_stream_memory_free queued 32512, sndbuf 30912
> sk_stream_wait_memory with 0 returned -11
> !sk_stream_memory_free queued 32512, sndbuf 30912
> sk_stream_wait_memory with 0 returned -11
> !sk_stream_memory_free queued 32512, sndbuf 30912
> sk_stream_wait_memory with 0 returned -11
> !sk_stream_memory_free queued 32512, sndbuf 30912
> sk_stream_wait_memory with 0 returned -11
> !sk_stream_memory_free queued 32512, sndbuf 30912
> sk_stream_wait_memory with 0 returned -11
> !sk_stream_memory_free queued 32512, sndbuf 30912
> sk_stream_wait_memory with 0 returned -11
> !sk_stream_memory_free queued 36576, sndbuf 34776
> sk_stream_wait_memory with 0 returned -11
> !sk_stream_memory_free queued 36576, sndbuf 34776
> sk_stream_wait_memory with 0 returned -11
> !sk_stream_memory_free queued 36576, sndbuf 34776
> sk_stream_wait_memory with 0 returned -11
> !sk_stream_memory_free queued 36576, sndbuf 34776
> sk_stream_wait_memory with 0 returned -11
> !sk_stream_memory_free queued 36576, sndbuf 34776
> sk_stream_wait_memory with 0 returned -11
> !sk_stream_memory_free queued 36576, sndbuf 34776
> sk_stream_wait_memory with 0 returned -11
> !sk_stream_memory_free queued 36576, sndbuf 34776
> sk_stream_wait_memory with 0 returned -11
> !sk_stream_memory_free queued 36576, sndbuf 34776
> sk_stream_wait_memory with 0 returned -11
> !sk_stream_memory_free queued 36576, sndbuf 34776
> sk_stream_wait_memory with 0 returned -11
> !sk_stream_memory_free queued 36576, sndbuf 34776
> sk_stream_wait_memory with 0 returned -11
> !sk_stream_memory_free queued 36576, sndbuf 34776
> sk_stream_wait_memory with 0 returned -11
>
> and so on and the sndbuf does not grow beyond 34776
So there is outstanding data(sk_wmem_queued) that is not getting
acked.
If you set the sndbuf manually to a higher value, does it solve
the problem or only delay the stalls?
Thanks
Sridhar
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