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From: Robert Fendt <fendt@physik.uni-dortmund.de>
To: linux-kernel@vger.kernel.org
Subject: Re: peculiar problem with 2.6, 8139too + ACPI
Date: Sun, 16 May 2004 01:30:39 +0200	[thread overview]
Message-ID: <20040516013039.52cad4ca.fendt@physik.uni-dortmund.de> (raw)
In-Reply-To: <1084584998.12352.306.camel@dhcppc4>

> It is possible that the system is getting into a high power saving
> mode on idle.  Device bus master activity or interrupts will wake
> it up -- but the latency to return from power savings mode may be
> so high that the device experiences receive buffer overruns.

Yes, I also thought in that direction, since the main difference between
the processor module loaded or not seems to be the idle handler.

> Some devices handle this latency better than others,
> and with a network, dropping RX packets can cause the
> connection to thrash, and it seems that is what you see.
> 
> If the 8139too has statistics counters showing if it gets
> RX buffer over-runs, that would be interseting to observe.

I seem to be unable to reproduce the problem on my home network. It is a
small (switched) 100BaseT network which is connected to the outside via an
asynchronous dsl line (128/768kbit). Maybe the different LAN topology or
the slow external link make the difference. I will retry on monday on the
corporate network. The latter is a large university net, with our section
consisting of 100BaseT-to-100BaseFX tranceiver switches. I do not have
information on the rest of the network.

> Also, to see what idle power saving states you have, their
> latency and their usage, please do this:
> cat /proc/acpi/processor/CPU0/power

betazed:~# cat /proc/acpi/processor/CPU1/power
active state:            C2
default state:           C1
bus master activity:     ffffffff
states:
    C1:                  promotion[C2] demotion[--] latency[000] usage[00000010]
   *C2:                  promotion[C3] demotion[C1] latency[001] usage[00025200]
    C3:                  promotion[--] demotion[C2] latency[101] usage[00024564]

> It would also be interesting to know if you see the problem
> more frequently when running on battery power, since some
> systems have higher c-state exit latency when on battery.

I cannot say at this moment, since I cannot reproduce the problem at home
(see above). I will try to get some info on this matter on monday. Stay
tuned.

> It would also be interesting to know if you see the same
> frequency of the problem on 2.4, since it has 100HZ clock
> vs 1000HZ clock on 2.6 -- and this can have a significant
> effect on the effectivness of idle c-states.

Will try to install a 2.4 kernel on the box and see what happens.

Regards,
Robert

  reply	other threads:[~2004-05-15 23:32 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <A6974D8E5F98D511BB910002A50A6647615FB5FE@hdsmsx403.hd.intel.com>
2004-05-15  1:36 ` Len Brown
2004-05-15 23:30   ` Robert Fendt [this message]
2004-05-17 10:30   ` Robert Fendt
2004-05-17 18:24     ` Len Brown
2004-05-17 19:10       ` Jeff Garzik
2004-05-20 23:53       ` Robert Fendt
2004-05-21  1:16         ` Len Brown
2004-05-27 13:45           ` Robert Fendt
2004-05-14 13:28 Robert Fendt

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