netdev - Re: [PATCH v2 net-next] tcp: avoid tx starvation by SYNACK packets

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Date:	Wed, 27 Jun 2012 10:21:15 +0200
From:	Jesper Dangaard Brouer <brouer@...hat.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>, hans.schillstrom@...csson.com,
	subramanian.vijay@...il.com, dave.taht@...il.com,
	netdev@...r.kernel.org, ncardwell@...gle.com, therbert@...gle.com,
	mph@...h.dk
Subject: Re: [PATCH v2 net-next] tcp: avoid tx starvation by SYNACK packets

On Wed, 2012-06-27 at 10:02 +0200, Eric Dumazet wrote:
> On Wed, 2012-06-27 at 09:54 +0200, Jesper Dangaard Brouer wrote:
> 
> > Well, that would lead to parallel SYN processing, wouldn't it?
> 
> I think we already discussed of the current issues of current code.
> 
> Telling people to spread SYN to several cpus is a good way to have a
> freeze in case of synflood, because 15 cpus are busy looping while one
> is doing progress.

Yes, that was also what I experienced (contention on spinlock), and then
tried to address it with my parallel SYN cookie patches, and it worked
amazing well...


> Thats why Intel felt the need of a hardware filter to direct all SYN
> packets on a single queue.

It works because we have a spinlock problem in the code... Perhaps, they
did it, because we have have locking/contention problem, not the other
way around ;-)  How about fixing the code instead? ;-)))




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