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

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Message-ID: <1340778733.2028.110.camel@localhost>
Date:	Wed, 27 Jun 2012 08:32:13 +0200
From:	Jesper Dangaard Brouer <brouer@...hat.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Hans Schillstrom <hans.schillstrom@...csson.com>,
	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>,
	Martin Topholm <mph@...h.dk>
Subject: Re: [PATCH v2 net-next] tcp: avoid tx starvation by SYNACK packets

On Tue, 2012-06-26 at 19:02 +0200, Eric Dumazet wrote:
> 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.

I'm using a 10G link

> > 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.

How are you avoiding the lock bh_lock_sock_nested(sk) in tcp_v4_rcv()?


> 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 my parallel SYN cookie/brownies patches, I could easily process 750
Kpps (limited by the generator, think the owners of the big machine did
a test where they reached 1400 Kpps).

I also had ~10% CPU usage from sha_transform() but across all cores...


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

IMHO a faster hash is not the answer... parallel processing of SYN
packets is a better answer.  But I do think, adding this faster hash as
a sysctl switch might be a good idea, for people with smaller embedded
hardware.  Using it as default, might be "dangerous" and open an attack
vector on SYN cookies in Linux.


-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Sr. Network Kernel Developer at Red Hat
  Author of http://www.iptv-analyzer.org
  LinkedIn: http://www.linkedin.com/in/brouer


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