netdev - Re: [PATCH 5/5 v4] net: add old_queue

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Date:	Tue, 21 Dec 2010 22:03:40 +0800
From:	Changli Gao <xiaosuo@...il.com>
To:	hadi@...erus.ca
Cc:	"David S. Miller" <davem@...emloft.net>,
	Stephen Hemminger <shemminger@...ux-foundation.org>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Tom Herbert <therbert@...gle.com>,
	Jiri Pirko <jpirko@...hat.com>, netdev@...r.kernel.org,
	netem@...ts.linux-foundation.org
Subject: Re: [PATCH 5/5 v4] net: add old_queue_mapping into skb->cb

On Tue, Dec 21, 2010 at 9:07 PM, jamal <hadi@...erus.ca> wrote:
> On Fri, 2010-12-17 at 21:41 +0800, Changli Gao wrote:
>
> Sorry for the latency - I am a little swamped.
>
>> I doubt it can work.
>
> It should work - this used to be part of my regression tests.
> If it doesnt work something is broken.

When I tested it, my OS got frozen.

>
> In any case, I shouldnt have used this example because
> it distracted from the point i was trying to make:
> You are restoring the old qmap when the point is we could change
> it to a new one. A simpler example illustrating how
> a qmap could be changed:
>
> ----
> tc filter add dev ifb0 parent 1:0 protocol ip prio 10 u32 \
>  match u32 0 0 flowid 1:2 \
>  action skbedit queue_mapping 4
> ----

Currently, you can only change the rx queue mapping, because for tx,
dev_pick_tx() doesn't use skb->queue_mapping to choose tx queue.

However, I don't think change the rx queue mapping is a good idea.
When the skbs returned from ifb enter netif_receive_skb() again,
get_rps_cpu() may warn about the wrong rx queue, and my this patch is
used to solve this problem. Even though the rx queue is legal, a
different rps_cpus settings will be used, and the skbs may be
redirected to different CPUs. Is it expected?


-- 
Regards,
Changli Gao(xiaosuo@...il.com)
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