netdev - Re: [PATCH] tcp: md5 signature check scaling

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Message-ID: <20101027085603.490e326b@nehalam>
Date:	Wed, 27 Oct 2010 08:56:03 -0700
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Dmitry Popov <dp@...hloadlab.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	William.Allen.Simpson@...il.com,
	Eric Dumazet <eric.dumazet@...il.com>,
	Andreas Petlund <apetlund@...ula.no>,
	Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	"Pekka Savola (ipv6)" <pekkas@...core.fi>,
	James Morris <jmorris@...ei.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Gilad Ben-Yossef <gilad@...efidence.com>,
	Yony Amit <yony@...sleep.com>, Zhu Yi <yi.zhu@...el.com>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH] tcp: md5 signature check scaling

On Wed, 27 Oct 2010 16:52:30 +0400
Dmitry Popov <dp@...hloadlab.com> wrote:

> From: Dmitry Popov <dp@...hloadlab.com>
> 
> TCP MD5 signature checking without socket lock.
> 
> Each tcp_sock has 2 RCU-protected arrays (tcp[46]_md5sig_info) of
> tcp[46]_md5sig_key address-key pairs.
> Each key (tcp_md5sig_key) has kref struct so that there is no need to
> lock the whole array to work with one key.
> 
> MD5 functions were rewritten according to above statement and hash
> check (tcp_v4_inbound_md5_hash) was moved before socket lock.
> 
> Signed-off-by: Dmitry Popov <dp@...hloadlab.com>

You traded locking for ref counting which may not be as big
a win as your think.

Also, the overhead of RCU here might impact tests that involve
lots of socket creation and destruction.

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