netdev - Re: [PATCH 3/3] pkt_sched: restore multiqueue prio scheduler

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Date:	Sat, 23 Aug 2008 17:07:11 +1000
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	alexander.duyck@...il.com (Alexander Duyck)
Cc:	herbert@...dor.apana.org.au, davem@...emloft.net,
	jarkao2@...il.com, hadi@...erus.ca, jeffrey.t.kirsher@...el.com,
	jeff@...zik.org, netdev@...r.kernel.org,
	alexander.h.duyck@...el.com
Subject: Re: [PATCH 3/3] pkt_sched: restore multiqueue prio scheduler

Alexander Duyck <alexander.duyck@...il.com> wrote:
> 
> It isn't the performance aspect of running everything through one
> queue that I am concerned about since that is how it was working
> before.  My concern is that the action could cause a dead lock if
> simple_tx_hash places traffic on 2 queues and then the tc rule tried
> to swap the traffic between those queues while they are each holding
> their own queue locks.  The tc rule would have to receive all traffic
> onto a single qdisc to prevent this, which would require setting
> select_queue for the netdev to return a fixed queue.  The multiqueue
> prio qdisc is flexible enough to allow all traffic to be directed to
> one queue or be received on multiple queues without causing the system
> to lock up which means that implementing select_queue on the device
> wouldn't be mandatory.

As it is if you create a custom qdisc then there will only be
a single qdisc no matter how many hardware queues you have.  So
you can safely dequeue from the qdisc into any hardware queue you
want.

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