From: Eric Dumazet <dada1@cosmosbay•com>
To: Wes Chow <wchow@athenacr•com>
Cc: netdev@vger•kernel.org
Subject: Re: Multicast packet loss
Date: Mon, 02 Feb 2009 22:31:41 +0100 [thread overview]
Message-ID: <4987663D.6080802@cosmosbay.com> (raw)
In-Reply-To: <4987610D.6040902@athenacr.com>
Wes Chow a écrit :
>
>
> Eric Dumazet wrote:
>> Wes Chow a écrit :
>>> (I'm Kenny's colleague, and I've been doing the kernel builds)
>>>
>>> First I'd like to note that there were a lot of bnx2 NAPI changes
>>> between 2.6.21 and 2.6.22. As a reminder, 2.6.21 shows tiny amounts
>>> of packet loss,
>>> whereas loss in 2.6.22 is significant.
>>>
>>> Second, some CPU affinity info: if I do like Eric and pin all of the
>>> apps onto a single CPU, I see no packet loss. Also, I do *not* see
>>> ksoftirqd show up on top at all!
>>>
>>> If I pin half the processes on one CPU and the other half on another
>>> CPU, one ksoftirqd processes shows up in top and completely pegs one
>>> CPU. My packet loss
>>> in that case is significant (25%).
>>>
>>> Now, the strange case: if I pin 3 processes to one CPU and 1 process
>>> to another, I get about 25% packet loss and ksoftirqd pins one CPU.
>>> However, one
>>> of the apps takes significantly less CPU than the others, and all
>>> apps lose the
>>> *exact same number of packets*. In all other situations where we see
>>> packet
>>> loss, the actual number lost per application instance appears random.
>>
>> You see same number of packet lost because they are lost at NIC level
>
> Understood.
>
> I have a new observation: if I pin processes to just CPUs 0 and 1, I see
> no packet loss. Pinning to 0 and 2, I do see packet loss. Pinning 2 and
> 3, no packet loss. 4 & 5 - no packet loss, 6 & 7 - no packet loss. Any
> other combination appears to produce loss (though I have not tried all
> 28 combinations, this seems to be the case).
>
> At first I thought maybe it had to do with processes pinned to the same
> CPU, but different cores. The machine is a dual quad core, which means
> that CPUs 0-3 should be a physical CPU, correct? Pinning to 0/2 and 0/3
> produce packet loss.
a quad core is really a 2 x 2 core
L2 cache is splited on two blocks, one block used by CPU0/1, other by CPU2/3
You are at the limit of the machine with such workload, so as soon as your
CPUs have to transfert 64 bytes lines between those two L2 blocks, you loose.
>
> I've also noticed that it does not matter which of the working pairs I
> pin to. For example, pinning 5 processes in any combination on either
> 0/1 produce no packet loss, pinning all 5 to just CPU 0 also produces no
> packet loss.
>
> The failures are also sudden. In all of the working cases mentioned
> above, I don't see ksoftirqd on top at all. But when I run 6 processes
> on a single CPU, ksoftirqd shoots up to 100% and I lose a huge number of
> packets.
>
>>
>> Normaly, softirq runs on same cpu (the one handling hard irq)
>
> What determines which CPU the hard irq occurs on?
>
Check /proc/irq/{irqnumber}/smp_affinity
If you want IRQ16 only served by CPU0 :
echo 1 >/proc/irq/16/smp_affinity
next prev parent reply other threads:[~2009-02-02 21:31 UTC|newest]
Thread overview: 70+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-01-30 17:49 Multicast packet loss Kenny Chang
2009-01-30 19:04 ` Eric Dumazet
2009-01-30 19:17 ` Denys Fedoryschenko
2009-01-30 20:03 ` Neil Horman
2009-01-30 22:29 ` Kenny Chang
2009-01-30 22:41 ` Eric Dumazet
2009-01-31 16:03 ` Neil Horman
2009-02-02 16:13 ` Kenny Chang
2009-02-02 16:48 ` Kenny Chang
2009-02-03 11:55 ` Neil Horman
2009-02-03 15:20 ` Kenny Chang
2009-02-04 1:15 ` Neil Horman
2009-02-04 16:07 ` Kenny Chang
2009-02-04 16:46 ` Wesley Chow
2009-02-04 18:11 ` Eric Dumazet
2009-02-05 13:33 ` Neil Horman
2009-02-05 13:46 ` Wesley Chow
2009-02-05 13:29 ` Neil Horman
2009-02-01 12:40 ` Eric Dumazet
2009-02-02 13:45 ` Neil Horman
2009-02-02 16:57 ` Eric Dumazet
2009-02-02 18:22 ` Neil Horman
2009-02-02 19:51 ` Wes Chow
2009-02-02 20:29 ` Eric Dumazet
2009-02-02 21:09 ` Wes Chow
2009-02-02 21:31 ` Eric Dumazet [this message]
2009-02-03 17:34 ` Kenny Chang
2009-02-04 1:21 ` Neil Horman
2009-02-26 17:15 ` Kenny Chang
2009-02-28 8:51 ` Eric Dumazet
2009-03-01 17:03 ` Eric Dumazet
2009-03-04 8:16 ` David Miller
2009-03-04 8:36 ` Eric Dumazet
2009-03-07 7:46 ` Eric Dumazet
2009-03-08 16:46 ` Eric Dumazet
2009-03-09 2:49 ` David Miller
2009-03-09 6:36 ` Eric Dumazet
2009-03-13 21:51 ` David Miller
2009-03-13 22:30 ` Eric Dumazet
2009-03-13 22:38 ` David Miller
2009-03-13 22:45 ` Eric Dumazet
2009-03-14 9:03 ` [PATCH] net: reorder fields of struct socket Eric Dumazet
2009-03-16 2:59 ` David Miller
2009-03-16 22:22 ` Multicast packet loss Eric Dumazet
2009-03-17 10:11 ` Peter Zijlstra
2009-03-17 11:08 ` Eric Dumazet
2009-03-17 11:57 ` Peter Zijlstra
2009-03-17 15:00 ` Brian Bloniarz
2009-03-17 15:16 ` Eric Dumazet
2009-03-17 19:39 ` David Stevens
2009-03-17 21:19 ` Eric Dumazet
2009-04-03 19:28 ` Brian Bloniarz
2009-04-05 13:49 ` Eric Dumazet
2009-04-06 21:53 ` Brian Bloniarz
2009-04-06 22:12 ` Brian Bloniarz
2009-04-07 20:08 ` Brian Bloniarz
2009-04-08 8:12 ` Eric Dumazet
2009-03-09 22:56 ` Brian Bloniarz
2009-03-10 5:28 ` Eric Dumazet
2009-03-10 23:22 ` Brian Bloniarz
2009-03-11 3:00 ` Eric Dumazet
2009-03-12 15:47 ` Brian Bloniarz
2009-03-12 16:34 ` Eric Dumazet
2009-02-27 18:40 ` Christoph Lameter
2009-02-27 18:56 ` Eric Dumazet
2009-02-27 19:45 ` Christoph Lameter
2009-02-27 20:12 ` Eric Dumazet
2009-02-27 21:36 ` Eric Dumazet
2009-02-02 13:53 ` Eric Dumazet
-- strict thread matches above, loose matches on Subject: below --
2009-04-05 14:42 bmb
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