| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Date: Wed, 14 May 2008 13:11:13 -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 5/14/08, Shirish Pargaonkar <shirishpargaonkar@...il.com> wrote:
> On 5/13/08, Sridhar Samudrala <sri@...ibm.com> wrote:
> > On Tue, 2008-05-13 at 08:54 -0500, Shirish Pargaonkar 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().
> > > >
> > > > 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.
> >
> > > Sridhar,
> > >
> > > The size of the sends is 56K.
> >
> > As David pointed out, the send size may not be an issue.
> > When do you see these stalls? Do they happen frequently or only under
> > stress?
> >
> > It could be that the receiver is not able to drain the receive queue
> > causing the send path to be blocked. You could run netstat -tn on
> > the receiver and take a look at 'Recv-Q' output to see if there is
> > data pending in the receive queue.
> >
> > Thanks
> > Sridhar
> >
> >
>
> These errors are logged during stress testing, not otherwise.
> I am running fsstress on 10 shares mounted on this machine running cifs client
> which are exported by a samba server on another machine.
>
> I was running netstat -tn on the machine running samba server in a while loop
> in a script untill errors started showing up on the cifs client.
> Some of the entries captured in the file are listed below, rest of them
> (34345 out of 34356 ) have Recv-Q as 0.
>
> tcp 10080 0 123.456.78.238:445 123.456.78.239:39538
> ESTABLISHED
> tcp 10080 0 123.456.78.238:445 123.456.78.239:39538
> ESTABLISHED
> tcp 10080 51 123.456.78.238:445 123.456.78.239:39538
> ESTABLISHED
> tcp 10983 7200 123.456.78.238:445 123.456.78.239:39538
> ESTABLISHED
> tcp 11884 10080 123.456.78.238:445 123.456.78.239:39538
> ESTABLISHED
> tcp 11925 1440 123.456.78.238:445 123.456.78.239:39538
> ESTABLISHED
> tcp 12116 7200 123.456.78.238:445 123.456.78.239:39538
> ESTABLISHED
> tcp 12406 0 123.456.78.238:445 123.456.78.239:39538
> ESTABLISHED
> tcp 290 0 123.456.78.238:445 123.456.78.239:39538
> ESTABLISHED
> tcp 5028 11627 123.456.78.238:445 123.456.78.239:39538
> ESTABLISHED
> tcp 8640 51 123.456.78.238:445 123.456.78.239:39538
> ESTABLISHED
>
> It is hard to match exact netstat -tn output on the machine running
> samba server
> with the errors on machine running cifs client but as soon as I saw the errors
> appearing on the client, I ran netstat -tn command on the server and found
> Recv-Q entry was 0 (may be the Recv-Q entries were processed/cleared by
> the samba server by then).
>
> Regards,
>
> Shirish
>
So I see high count of bytes not copied by the user program but they are
read next time netstat -tn is run (within probably less than a
second), so it is not
as if the samba server is not reading off data for long periods right?
Active Internet connections (w/o servers)
Proto Recv-Q Send-Q Local Address Foreign Address
State
tcp 0 164 123.456.78.238:445 123.456.78.239:39538
ESTABLISHED
tcp 0 0 ::ffff:123.456.78.238:22
::ffff:123.456.78.190:34532 ESTABLISHED
tcp 0 0 ::ffff:123.456.78.238:22
::ffff:123.456.78.135:50328 ESTABLISHED
tcp 0 0 ::ffff:123.456.78.238:22
::ffff:123.456.78.135:50333 ESTABLISHED
Active Internet connections (w/o servers)
Proto Recv-Q Send-Q Local Address Foreign Address
State
tcp 12406 0 123.456.78.238:445 123.456.78.239:39538
ESTABLISHED
tcp 0 0 ::ffff:123.456.78.238:22
::ffff:123.456.78.190:34532 ESTABLISHED
tcp 0 0 ::ffff:123.456.78.238:22
::ffff:123.456.78.135:50328 ESTABLISHED
tcp 0 0 ::ffff:123.456.78.238:22
::ffff:123.456.78.135:50333 ESTABLISHED
Active Internet connections (w/o servers)
Proto Recv-Q Send-Q Local Address Foreign Address
State
tcp 0 0 123.456.78.238:445 123.456.78.239:39538
ESTABLISHED
tcp 0 0 ::ffff:123.456.78.238:22
::ffff:123.456.78.190:34532 ESTABLISHED
tcp 0 0 ::ffff:123.456.78.238:22
::ffff:123.456.78.135:50328 ESTABLISHED
tcp 0 0 ::ffff:123.456.78.238:22
::ffff:123.456.78.135:50333 ESTABLISHED
So are these occasional and short-lived spikes in unread data on the
server side
causing from send buffer from increasing on the client side?
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
Powered by blists - more mailing lists