netdev - Re: [RFC] multiqueue changes

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Date:	Mon, 2 Nov 2009 12:30:29 +0000
From:	Jarek Poplawski <jarkao2@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	mchan@...adcom.com, kaber@...sh.net, eric.dumazet@...il.com,
	netdev@...r.kernel.org
Subject: Re: [RFC] multiqueue changes

On Mon, Nov 02, 2009 at 03:35:33AM -0800, David Miller wrote:
> From: Jarek Poplawski <jarkao2@...il.com>
> Date: Sun, 1 Nov 2009 14:20:17 +0100
> 
> > There is a question if we can predict in ->probe() MSI-X should be
> > successfully enabled in ->ndo_open() for probed hardware. If so,
> > then it could go e.g. like this:
> 
> We never can know this.
> 
> Another device driver can eat up all the MSI-X vectors in the PCI
> domain before we make the request_irq() calls in ->open().

Right, but it's not a 50% chance, I guess? A user most of the time
gets consistently multiqueue or non-multiqueue behavior after open,
unless I miss something. Then such an exceptional state could be
handled by real_num_tx_queues (just like in case of powered of cpus).
The main difference is to hold in num_tx_queues something that is
really available vs max possible value for all configs.

Jarek P. 
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