netdev - Re: High contention on the sk_buff

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Date:	Thu, 2 Apr 2009 22:13:42 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	David Miller <davem@...emloft.net>
Cc:	dada1@...mosbay.com, jarkao2@...il.com, vernux@...ibm.com,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-rt-users@...r.kernel.org
Subject: Re: High contention on the sk_buff_head.lock

David Miller <davem@...emloft.net> wrote:
> From: Eric Dumazet <dada1@...mosbay.com>
> Date: Mon, 23 Mar 2009 09:32:39 +0100
> 
>> I dont understand, doesnt it defeat the ticket spinlock thing and fairness ?
>> 
>> Thread doing __qdisc_run() already owns the __QDISC_STATE_RUNNING bit.
> 
> Right.
> 
> Remember, the way this is designed is that if there is a busy
> cpu taking packets out of the queue and putting them into the
> device then other cpus will simply add to the queue and immediately
> return.  This effectively keeps the queue running there processing
> all the new work that other cpus are adding to the qdisc.
> 
> Those other cpus make these decisions by looking at that
> __QDISC_STATE_RUNNING bit, which the queue runner grabs before
> it does any work.

Come on guys, if this lock is a problem. go out and buy a proper
NIC that supports multiequeue TX!

Cheers,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
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