netdev - Re: TCP-MD5 checksum failure on x86

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Date:	Thu, 06 May 2010 14:06:26 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Bhaskar Dutta <bhaskie@...il.com>
Cc:	Stephen Hemminger <shemminger@...tta.com>,
	Ben Hutchings <bhutchings@...arflare.com>,
	netdev@...r.kernel.org
Subject: Re: TCP-MD5 checksum failure on x86_64 SMP

Le jeudi 06 mai 2010 à 17:25 +0530, Bhaskar Dutta a écrit :

> I put in the above change and ran some load tests with around 50
> active TCP connections doing MD5.
> I could see only 1 bad packet in 30 min (earlier the problem used to
> occur instantaneously and repeatedly).
> 
> I think there is another possibility of being preempted when calling
> tcp_alloc_md5sig_pool()
> this function releases the spinlock when calling __tcp_alloc_md5sig_pool().
> 
> I will run some more tests after changing the  tcp_alloc_md5sig_pool
> and see if the problem is completely resolved.
> 

This code should be completely rewritten for linux-2.6.35, its very ugly
and over complex, yet it is not scalable.

It could use true percpu data, with no central lock or refcount.



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