netdev - Re: TCP slowdown in 2.6.25?

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Message-ID: <Pine.LNX.4.64.0804281728280.1888@wrl-59.cs.helsinki.fi>
Date:	Mon, 28 Apr 2008 17:42:45 +0300 (EEST)
From:	"Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
To:	Joakim Tjernlund <joakim.tjernlund@...nsmode.se>
cc:	Netdev <netdev@...r.kernel.org>
Subject: Re: TCP slowdown in 2.6.25?

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)?

Do you have network namespaces enabled in .config?

Netfilter/iptables involved?

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

-- 
 i.
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