netdev - Re: [RFC] multiqueue changes

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Date:	Thu, 29 Oct 2009 23:12:39 +0100
From:	Patrick McHardy <kaber@...sh.net>
To:	Jarek Poplawski <jarkao2@...il.com>
CC:	Eric Dumazet <eric.dumazet@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Linux Netdev List <netdev@...r.kernel.org>
Subject: Re: [RFC] multiqueue changes

Jarek Poplawski wrote:
> On Thu, Oct 29, 2009 at 05:37:23PM +0100, Patrick McHardy wrote:
> ...
>> Well, we do need both values for supporting changes to the actually
>> used numbers of TX queues. If I understood Dave's explanation correctly,
>> this is also what's intended. It also doesn't seem unreasonable
>> what bnx2 is doing.
> 
> Exactly. With a growing number of cores, both available and powered
> off, these values will be soon treated more carefully than now.
> 
>> But getting back to the problem Eric reported - so you're suggesting
>> that bnx2.c should also adjust num_tx_queues in case the hardware
>> doesn't support multiqueue? That seems reasonable as well.
> 
> Currently, declaring num_tx_queues with alloc_netdev_mq() looks like
> too soon for some drivers. It seems they should be able to do it
> separately later during the .probe.

The value passed into alloc_netdev_mq() is just used for allocation
purposes, from what I can tell there's no downside in reducing it
before the dev_activate() call.

> There is a question if .ndo_open should be considered too.

I currently can't see any purpose in decreasing num_tx_queues after
registration instead of real_num_tx_queues. But it depends on how
exactly this will be implemented and how it interacts with qdiscs
(hence me previous mail, where I tried to point out possible
inconsistencies from using real_num_tx_queues).
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