netdev - Re: [PATCH net-next] icmp: add a global rate limitation

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Message-Id: <20140922.160904.1566383839759663411.davem@davemloft.net>
Date:	Mon, 22 Sep 2014 16:09:04 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH net-next] icmp: add a global rate limitation

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Fri, 19 Sep 2014 07:38:40 -0700

> Current ICMP rate limiting uses inetpeer cache, which is an RBL tree
> protected by a lock, meaning that hosts can be stuck hard if all cpus
> want to check ICMP limits.

However, the replacement uses a single global spinlock for
synchronization.

 ...
> Note that if we really want to send millions of ICMP messages per
> second, we might extend idea and infra added in commit 04ca6973f7c1a
> ("ip: make IP identifiers less predictable") :
> add a token bucket in the ip_idents hash and no longer rely on inetpeer.

That would be preferred.

I don't really see how this patch makes things better.  The code goes
through a global spinlock unconditionally, and if it passes then it
looks up the inetpeer anyways.

I need more information to be convinced that this is an improvement
and that it actually solves the stated problem.  I'm sure you also
have some performance metrics to share, right? :-)

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