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

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Date:	Wed, 4 Jun 2014 14:26:58 -0400
From:	sowmini varadhan <sowmini05@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	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 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?

> [1] Well, sort of : prediction was : it's so easy to remotely crash the
> host.

--Sowmini
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