netdev - Re: Fwd: Linux stack performance drop (TCP and UDP) in 3.10 kernel in routed scenario

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Message-ID: <CADVnQy=cdg2ZmwAFoMpZv4VrpY++bW-Sj3krzqvXKVjM3=zqZg@mail.gmail.com>
Date:	Wed, 4 Jun 2014 14:32:20 -0400
From:	Neal Cardwell <ncardwell@...gle.com>
To:	sowmini varadhan <sowmini05@...il.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Suprasad Mutalik Desai <suprasad.desai@...il.com>,
	netdev <netdev@...r.kernel.org>,
	David Miller <davem@...emloft.ne>
Subject: Re: Fwd: Linux stack performance drop (TCP and UDP) in 3.10 kernel in
 routed scenario

On Wed, Jun 4, 2014 at 2:26 PM, sowmini varadhan <sowmini05@...il.com> wrote:
> On Wed, Jun 4, 2014 at 10:59 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
>
>> Problem with IPv4 route cache is that is was too easy to flood it and
>> get worse performance.
>>
>> It had simply huge memory costs, and non predictable behavior [1]
>
> Can you elaborate? Caches usually have an upper bound on
> the memory to be consumed by the cache, and from my reading
> of the 2.6.32 code, seems like it also had such limits (there was
> a sysctl tunable to turn off hashing, and rt_intern_hash() also had
> other bounds. Were these not enough?

David put together a nice presentation that covers a lot of the topics
in this thread:

  Removing The Linux Routing Cache
  David S. Miller, 2012
  http://vger.kernel.org/~davem/columbia2012.pdf

neal
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