netdev - ksoftirqd 100% after disabling IPv4 route cache on high pps.

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Date:	Wed, 5 Dec 2012 13:22:45 -0800
From:	叶雨飞 <sunyucong@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	netdev <netdev@...r.kernel.org>
Subject: ksoftirqd 100% after disabling IPv4 route cache on high pps.

Hi Eric,

After disabling the route cache, I found a forwarding performance
problem (inevitable ?). Basically the kernel couldn't keep up under
about 100k pps and ksoftirqd is dominating the CPU. This problem went
away right away if I do

echo  1 > rt_cache_rebuild_count

and comes back as soon as i do echo -1 > rt_cache_rebuild_count.

I then tried to use RPS/RFS to share the load on to mulitple cpus
(since ksoftirqd is only using 1 core, clearly). but that has little
effect.

Is there some tweaks/patches you recommend?

Thanks in advance.

On Tue, Nov 27, 2012 at 5:34 PM, 叶雨飞 <sunyucong@...il.com> wrote:
> Thanks!!! it works, after flushing cache it stays 0.
>
> On Tue, Nov 27, 2012 at 5:01 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
>> On Tue, 2012-11-27 at 15:15 -0800, 叶雨飞 wrote:
>>> Hi,
>>>
>>> I have a linux router running kernel 3.2  that receive public ingress
>>> packets and route them through an GRE tunnel, return packets don't go
>>> through it
>>>
>>> I've recently faced a serious issue with the route cache,  when the
>>> router received spoofed source , the route cache will quickly get
>>> exhausted (depending on the size of it) and soon the ip dst cache
>>> overflow will be printed and network subsystem will hang until
>>> restarted.
>>>
>>> So, my question is, how can I turn off the route cache without
>>> recompile the kernel or adding the  patch for removal  in 3.7?  I
>>> tried to set
>>>
>>> echo 0 > /proc/sys/net/ipv4/route/max_size but that has no effect at all.
>>>
>>> And if some one can share some insight on why when dst cache
>>> overflows, the network subsystem hangs, it would be great.
>>
>> echo -1 >/proc/sys/net/ipv4/rt_cache_rebuild_count
>>
>>
>>
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