netdev - Re: [PATCH] Multiqueue macvtap driver

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Date:	Sun, 01 Aug 2010 00:34:06 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	bhutchings@...arflare.com
Cc:	krkumar2@...ibm.com, arnd@...db.de, netdev@...r.kernel.org,
	mst@...hat.com
Subject: Re: [PATCH] Multiqueue macvtap driver

From: Ben Hutchings <bhutchings@...arflare.com>
Date: Sat, 31 Jul 2010 20:18:27 +0100

> 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.

Agreed.
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