Packet drop while using BPF filter

From: raghu.prabhu13@gmail.com (Raghavendra D Prabhu)
To: kernelnewbies@lists.kernelnewbies.org
Subject: Packet drop while using BPF filter
Date: Sun, 25 Dec 2011 00:24:45 +0530	[thread overview]
Message-ID: <20111224185445.GC35489@Xye> (raw)
In-Reply-To: <CACPS-PuywThT4aHZdia4HtJoLBjA1jbyxU5q+KCBm5RKoCRitQ@mail.gmail.com>

* On Sat, Dec 24, 2011 at 09:57:50PM +0530, Mukesh Yadav <mukesh.fkd@gmail.com> wrote:
>Hi  Raghavendra,
>
>" /proc/sys/net/core/bpf_jit_**enable " is not present on machine. Seems
>kernel need to be configured for these.
Yes, it is a fairly new option -- CONFIG_BPF_JIT=y

>Btw CPU scaling issue is resolved. Packet drop was because all interrupt
>handling was happening on core where packets were getting drop. Tuning
>system for interrupt handling using smp_affinity resolved the issue.
That is generally how it is done. The core which handles packets 
initially
handles the interrupts too. Do you mean all non-network 
interrupts were happening on same core ? Then give irqbalance a 
shot.

>
>Thanks
>Mukesh
>
>On 22 December 2011 19:18, Raghavendra D Prabhu <raghu.prabhu13@gmail.com>wrote:
>
>> Hi,

>>    Have you tried enabling -- /proc/sys/net/core/bpf_jit_**enable --
>>    provides JIT compiled BPF  on 64 bit linux.


>> * On Wed, Dec 21, 2011 at 12:08:04AM +0530, Mukesh Yadav <
>> mukesh.fkd at gmail.com> wrote:

>>> Hi Guys,

>>> I am working on user level code which uses BPF filter.
>>> Solution has two threads and  BPF filter for incoming packets to raw
>>> socket
>>> dedicated to each thread.
>>> Intent is to divide ingress traffic between two thread based on whether
>>> dest IP is even or odd.

>>> BPF filters used are:
>>> Even IP filter :-> tcpdump -i interface 'ether dst <dest mac> && ip[19] &
>>> 0x01 = 0'
>>> Odd IP filter :->  tcpdump -i interface  'ether dst <dest mac> && ip[19] &
>>> 0x01 = 1'

>>> There is a packet loss for odd IP thread even when CPU is available.
>>> Reason
>>> being packet drop due  recv buffer full.
>>> Same amount of traffic is well handled by even IP thread(user code being
>>> same in both), scaling CPU to full 100%.

>>> In odd IP thread, If filter is changed to "tcpdump -i interface  'ether
>>> dst
>>> <dest mac> && ip proto 17' ", all goes fine.
>>> Also CPU usage at kernel drops from 50% to 4 % for a particular amount of
>>> traffic.

>>> Would appreciate any I/ps for reducing load at kernel for packet
>>> filtering(Odd/Even IP distribution)


>>> Cheers
>>> Mukesh


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>> --------------------------
>> Raghavendra Prabhu
>> GPG Id : 0xD72BE977
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>> www: wnohang.net
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