netdev - Re: TCP slowdown in 2.6.25?

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Date:	Mon, 28 Apr 2008 17:19:19 +0200
From:	Joakim Tjernlund <joakim.tjernlund@...nsmode.se>
To:	Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>
Cc:	Netdev <netdev@...r.kernel.org>
Subject: Re: TCP slowdown in 2.6.25?


On Mon, 2008-04-28 at 17:42 +0300, Ilpo Järvinen wrote:
> On Mon, 28 Apr 2008, Joakim Tjernlund wrote:
> > On Mon, 2008-04-28 at 14:12 +0200, Joakim Tjernlund wrote:
> > > After upgrading from 2.6.23 to 2.6.25 I am seeing a big slow down on
> > > our old www server. Stracing shows lots of EAGAIN but i not sure
> > > these are relevant. I got no idea where to start looking so
> > > I would appreciate some pointers. Perhaps this is a know issue?
> > > 
> > > CPU is a PowerPC, mpc8321, network driver ucc_geth
> > 
> > Some info:
> > Even ftp transfers takes forever, but only in one direction: from the
> > node with kernel 2.6.25 to some other host. Strace show me that
> > write(2) hangs for long periods before succeeding to transmit 
> > the data.
> 
> Since it's easy, can you quickly try to if setting tcp_sack sysctl to 0 
> makes any difference (I made a surgery there, perhaps some bug in there 
> could cause TCP to recover by RTO multiple times in a row, that should 
> be visible in tcpdump as well)?

echo 0 > /proc/sys/net/ipv4/tcp_sack
did not make a difference, same problem.


> 
> Do you have network namespaces enabled in .config?

No,
# CONFIG_NAMESPACES is not set

> 
> Netfilter/iptables involved?

Some support compiled into the kernel, but no one is using it.

> 
> To some specific or "any" other host? How long is "long"?

Any host. A 1304632 bytes file takes about 110 seconds to transfer
(12 Kbytes/sec)

Thanks for helping.

A quick capture with wireshark indicates that some sent packages from
the node never reaches the host on the network.
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