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Message-ID: <49E78C1E.9060405@cosmosbay.com>
Date: Thu, 16 Apr 2009 21:50:54 +0200
From: Eric Dumazet <dada1@...mosbay.com>
To: Christoph Lameter <cl@...ux.com>
CC: netdev@...r.kernel.org
Subject: Re: Network latency regressions from 2.6.22 to 2.6.29
Eric Dumazet a écrit :
> Christoph Lameter a écrit :
>> The following are results of lantency measurements using udpping
>> (available from http://gentwo.org/ll). It shows that significant latencies
>> were added since 2.6.27. I surely wish we could get back to times below 90
>> microseconds.
>>
>> The tests were done over 1G ethernet using
>> 09:00.0 Ethernet controller: Broadcom Corporation NetXtreme BCM5754
>> Gigabit Ethernet PCI Express (rev 02)
>>
>> Results:
>>
>> 2.6.22 2.6.23 2.6.24 2.6.25 2.6.26 2.6.27 2.6.28 2.6.29
>> 40 Bytes 89.50 90.75 89.61 91.51 91.89 99.17 99.80 99.34
>> 400 Bytes 98.58 101.44 97.85 99.61 100.36 117.96 118.10 126.79
>> 1400 Bytes 152.76 153.75 153.85 156.22 156.66 163.92 165.54 166.04
>>
>> Compared to 2.6.22 2.6.23 2.6.24 2.6.25 2.6.26 2.6.27 2.6.28 2.6.29
>> 40 Bytes -1.4% -0.1% -2.2% -2.6% -9.8% -10.3% -9.9%
>> 400 Bytes -2.8% 0.7% -1.0% -1.8% -16.4% -16.5%-22.2%
>> 1400 Bytes -0.6% -0.7% -2.2% -2.5% -6.8% -7.7% -8.0%
>>
>> I presented these numbers with some nice graphs at the Linux Collab Summit
>> last week.
>>
>> See
>> http://www.kernel.org/pub/linux/kernel/people/christoph/collab-spring-2009/Collab-summit-2009-sf.pdf
>>
>
> Is it a bnx2 or tg3 driver ?
>
> copybreak feature could explain a regression for small packets, since
> an extra copy is done.
>
> It would be sane to always set on both machines :
> ethtool -C eth0 rx-usecs 0 rx-frames 1
> prior to your tests...
>
Also you might check /proc/interrupts, because recent linux versions are
distributing interrupts on all cpus instead of one on previous version
Old kernel :
# grep eth1 /proc/interrupts
58: 25754498 0 0 0 0 0 0 0 PCI-MSI eth1
New kernel :
# grep eth1 /proc/interrupts
221: 16476622 16478581 16478007 16478793 16478237 16472191 16474083 16476374 PCI-MSI-edge eth1
(and /proc/irq/221/smp_affinity is not taken into account on some NICS)
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