linux-kernel - Re: High contention on the sk_buff

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Message-ID: <20090323085058.GC4976@ff.dom.local>
Date:	Mon, 23 Mar 2009 08:50:58 +0000
From:	Jarek Poplawski <jarkao2@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	dada1@...mosbay.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

On Mon, Mar 23, 2009 at 01:37:49AM -0700, David Miller 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.

But this "busy cpu" can't take packets out of the queue when it's
waiting on the contended spinlock. Anyway, it's only for testing,
and I didn't say it has to be right.

Jarek P.
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