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

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Date:	Wed, 05 Dec 2012 15:48:51 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	叶雨飞 <sunyucong@...il.com>
Cc:	netdev <netdev@...r.kernel.org>
Subject: Re: ksoftirqd 100% after disabling IPv4 route cache on high pps.

On Wed, 2012-12-05 at 13:22 -0800, 叶雨飞 wrote:
> 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?

Yes, upgrade your kernel to 3.6 or 3.7, this problem has been solved for
good. No more IP route cache and good performance.

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