netdev - Re: [PATCH] NET: [UPDATED] Multiqueue network device support implementation.

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Message-ID: <461C766E.5030107@trash.net>
Date:	Wed, 11 Apr 2007 07:47:26 +0200
From:	Patrick McHardy <kaber@...sh.net>
To:	"Waskiewicz Jr, Peter P" <peter.p.waskiewicz.jr@...el.com>
CC:	davem@...emloft.net, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, jgarzik@...ox.com,
	cramerj <cramerj@...el.com>,
	"Kok, Auke-jan H" <auke-jan.h.kok@...el.com>,
	"Leech, Christopher" <christopher.leech@...el.com>
Subject: Re: [PATCH] NET: [UPDATED] Multiqueue network device support implementation.

Waskiewicz Jr, Peter P wrote:
>>This leaks the device. You treat every single-queue device as 
>>having a single subqueue. If it doesn't get too ugly it would 
>>be nice to avoid this and only allocate the subqueue states 
>>for real multiqueue devices.
> 
> 
> We went back and forth on this.  The reason we allocate a queue in every
> case, even on single-queue devices, was to make the stack not have
> branching for multiqueue and non-multiqueue devices.  If we don't have
> at least one queue on a device, then we can't have
> netif_subqueue_stopped() in the hotpath unless we check if a device is
> multiqueue before.  The original patches I released had this branching,
> and I was asked to not do that.


OK, thanks for the explanation.

>>>+			skb->queue_mapping =
>>>+				 q->prio2band[q->band2queue[band&TC_PRIO_MAX]];
>>
>>
>>Does this needs to be cleared at some point again? TC actions 
>>might redirect or mirror packets to other (multiqueue) devices.
> 
> 
> If an skb is redirected to another device, the skb should be filtered
> through that device's qdisc, yes?


Yes, but the device might not have a queue or use something different
than prio, so the value would stay the same. I think you need to clear
it before enqueueing a packet or alternatively when redirecting in the
mirred action.

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