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

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Date:	Tue, 26 Jun 2012 19:02:36 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Hans Schillstrom <hans.schillstrom@...csson.com>
Cc:	David Miller <davem@...emloft.net>,
	"subramanian.vijay@...il.com" <subramanian.vijay@...il.com>,
	"dave.taht@...il.com" <dave.taht@...il.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"ncardwell@...gle.com" <ncardwell@...gle.com>,
	"therbert@...gle.com" <therbert@...gle.com>,
	"brouer@...hat.com" <brouer@...hat.com>
Subject: Re: [PATCH v2 net-next] tcp: avoid tx starvation by SYNACK packets

On Tue, 2012-06-26 at 07:34 +0200, Hans Schillstrom wrote:

> This patch didn't give much in gain actually.

With a 100Mbps link it does.

With a 1Gbps link we are cpu bounded for sure.

> The big cycle consumer during a syn attack is SHA sum right now, 
> so from that perspective it's better to add aes crypto (by using AES-NI) 
> to the syn cookies instead of SHA sum. Even if only newer x86_64 can use it.

My dev machine is able to process ~280.000 SYN (and synack) per second
(tg3, mono queue), and sha_transform() takes ~10 % of the time according
to perf.

With David patch using jhash instead of SHA, I reach ~315.000 SYN per
second.



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