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Date: Thu, 15 May 2008 13:03:26 -0500 From: "Shirish Pargaonkar" <shirishpargaonkar@...il.com> To: "Sridhar Samudrala" <sri@...ibm.com> Cc: linux-net@...r.kernel.org, netdev@...r.kernel.org Subject: Re: autotuning of send buffer size of a socket On 5/15/08, Sridhar Samudrala <sri@...ibm.com> wrote: > 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 > > Sridhar, snd_cwnd goes from 6 to 7 to 8 to 9 and is capped at that value. That is how sndbuf grows upto but does not grow beyond 34776. If I set the sndbuf manully, it just delays stalls. I have gone as high as 1MB of send size and that prevents from logging these errors longer but eventually it does. Regards, Shirish -- 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
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