linux-kernel - Re: 2.6.25-rc6-git2: warn_on_slowpath for tcp_simple

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Date:	Wed, 2 Apr 2008 22:09:20 +0200
From:	"Alessandro Suardi" <alessandro.suardi@...il.com>
To:	"Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
Cc:	"Linux Kernel" <linux-kernel@...r.kernel.org>,
	Netdev <netdev@...r.kernel.org>
Subject: Re: 2.6.25-rc6-git2: warn_on_slowpath for tcp_simple_retransmit

On Wed, Apr 2, 2008 at 10:10 AM, Ilpo Järvinen
<ilpo.jarvinen@...sinki.fi> wrote:
> On Wed, 2 Apr 2008, Alessandro Suardi wrote:
>
>  > Found this in my FC6-based bittorrent box (K7-800 running
>  >  a 2.6.25-rc6-git2 kernel) this evening.
>  >
>  > The kernel was upgraded two weeks ago to fix the bug
>  >  in which an USB VIA driver hammered the PCI bus
>  >  causing ATA disk performance to drop, and has been
>  >  running since then (it still is).
>  >
>  > So it's actually 2.6.25-rc6-git2 plus patch as in here
>  > http://www.gossamer-threads.com/lists/linux/kernel/895506#895506
>  >
>  > If there's anything useful I can do, just ask. Thanks !
>
>  Can you reproduce?

Nope. That only happened once in this uptime:

[root@...key ~]# uptime
 21:57:21 up 14 days, 22:04,  5 users,  load average: 0.64, 0.47, 0.44

The machine runs unattended as a bittorrent client, 24x7,
 with a very low traffic (uploading at a steady ~36KB/s,
 and downloads happen in peaks).

I VNC into it in the evening and manage the torrents;
 that is all.

Now, there's an interesting tidbit:

[root@...key ~]# ip -s link show eth0
3: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast qlen 1000
    link/ether 00:c0:49:a7:33:fe brd ff:ff:ff:ff:ff:ff
    RX: bytes  packets  errors  dropped overrun mcast
    959044156  60549131 0       0       0       0
    TX: bytes  packets  errors  dropped carrier collsns
    744533957  66149681 0       0       0       0

[root@...key ~]# ifconfig eth0
eth0      Link encap:Ethernet  HWaddr 00:C0:49:A7:33:FE
          inet addr:192.168.1.7  Bcast:192.168.1.255  Mask:255.255.255.0
          inet6 addr: fe80::2c0:49ff:fea7:33fe/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:60551468 errors:0 dropped:0 overruns:0 frame:0
          TX packets:66152721 errors:0 dropped:0 overruns:1 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:959199592 (914.7 MiB)  TX bytes:748395356 (713.7 MiB)
          Interrupt:12 Base address:0xce00

Somehow the "overruns" counter is seen differently by 'ip'
 and 'ifconfig' - one says 0, the other says 1 - perhaps the
 packet that WARN'd me on tcp_simple_retransmit ?

If there's anything else - reproducing seems really really
 unlikely - 1 packet in 66 million...

Thanks,

--alessandro

 "Hold back the years, hold back the hours
 I want to live to see the sun break through these days"

 (Patrick Wolf, 'This Weather')
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