netdev - Re: [PATCH] Multiqueue macvtap driver

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Date:	Sat, 31 Jul 2010 20:18:27 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Krishna Kumar <krkumar2@...ibm.com>
Cc:	davem@...emloft.net, arnd@...db.de, netdev@...r.kernel.org,
	mst@...hat.com
Subject: Re: [PATCH] Multiqueue macvtap driver

On Sat, 2010-07-31 at 19:27 +0530, Krishna Kumar wrote:
[...]
> @@ -136,39 +158,68 @@ static void macvtap_put_queue(struct mac
>  }
>  
>  /*
> - * Since we only support one queue, just dereference the pointer.
> + * Select a queue based on the rxq of the device on which this packet
> + * arrived. If the incoming device is not mq, then use our cpu number
> + * to select a queue. vlan->numvtaps is cached in case it changes
> + * during the execution of this function.
>   */
[...]

This can result in reordering if a single-queue device's RX interrupt's
CPU affinity is changed.  We generally try to avoid that.  You should
really use or generate a flow hash.  There is code for this in
net/core/dev.c:get_rps_cpu() which could be factored out into a separate
function.

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare Communications
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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