netdev - Re: [PATCH net-next v3] packet: packet fanout rollover during socket overload

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Date:	Wed, 20 Mar 2013 02:37:59 -0400
From:	Willem de Bruijn <willemb@...gle.com>
To:	David Miller <davem@...emloft.net>
Cc:	Eric Dumazet <eric.dumazet@...il.com>, netdev@...r.kernel.org
Subject: Re: [PATCH net-next v3] packet: packet fanout rollover during socket overload

On Tue, Mar 19, 2013 at 5:34 PM, Willem de Bruijn <willemb@...gle.com> wrote:
> On Tue, Mar 19, 2013 at 5:16 PM, David Miller <davem@...emloft.net> wrote:
>> From: Eric Dumazet <eric.dumazet@...il.com>
>> Date: Tue, 19 Mar 2013 13:37:17 -0700
>>
>>> On Tue, 2013-03-19 at 16:18 -0400, Willem de Bruijn wrote:
>>>> Changes:
>>>>   v3->v2: rebase (no other changes)
>>>>           passes selftest
>>>>   v2->v1: read f->num_members only once
>>>>           fix bug: test rollover mode + flag
>>  ...
>>>> Signed-off-by: Willem de Bruijn <willemb@...gle.com>
>>  ...
>>> Reviewed-by: Eric Dumazet <edumazet@...gle.com>
>>
>> Applied, and I added the selftest too
>
> Thanks!
>
>>, but it fails for me on my
>> 128-cpu sparc64 machine:
>>
>> make[1]: Entering directory `/home/davem/src/GIT/net-next/tools/testing/selftests/net-afpacket'
>> --------------------
>> running psock_fanout test
>> --------------------
>> test: control single socket
>> test: control multiple sockets
>> test: datapath 0x0
>> info: count=0,0, expect=0,0
>> info: count=0,20, expect=15,5
>> ERROR: incorrect queue lengths
>
> I'm looking into it. The test needs the packet sockets to be able to
> hold an exact number of test packets and then overflow. Queue
> length configured in bytes (SO_RCVBUF) was arrived at by
> experimentation. My best hunch so far is that this differs between
> platforms/nic, if skb->truesize does. If queue length is the problem,
> I'll switch to a packet ring. Booting another machine right now.

I was able to reproduce this. The issue is not queue length, but an
rxhash collision. The test either passes or fails consistently between
reboots. Rebooting to get a different hashrnd seed may change the test
outcome.

Before finding this, I had already updated the patch to use a packet
ring (still better than the estimated queue length) and added
testcases for the LB and CPU modes. I may need to clean it up, but I
will send the current patch to see if it resolves the bug.


>> [FAIL]
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