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

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Message-ID: <1292945075.2720.32.camel@edumazet-laptop>
Date:	Tue, 21 Dec 2010 16:24:35 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Changli Gao <xiaosuo@...il.com>
Cc:	hadi@...erus.ca, "David S. Miller" <davem@...emloft.net>,
	Stephen Hemminger <shemminger@...ux-foundation.org>,
	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

Le mardi 21 décembre 2010 à 22:03 +0800, Changli Gao a écrit :
> 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?
> 
> 

Do we really want a multi queue ifb at all ?

Why not use percpu data and LLTX, like we did for other virtual devices
(loopback, tunnels, vlans, ...)

I guess most ifb uses need to finaly deliver packets in a monoqueue
anyway, optimizing ifb might raise lock contention on this resource.

See what we did in commit 79640a4ca6955e3e (net: add additional lock to
qdisc to increase throughput) : Adding one spinlock actually helped a
lot ;)



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