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

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Date:	Thu, 23 Dec 2010 08:21:43 -0500
From:	jamal <hadi@...erus.ca>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Changli Gao <xiaosuo@...il.com>,
	"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

On Tue, 2010-12-21 at 16:24 +0100, Eric Dumazet wrote:

> 
> 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.

I guess once you start having hardware that is multiqueue on the ingress
side at least then something per cpu is needed on ifb. But i agree that
the optimizations may end up harming the simplicity that ifb intended.
It is already jumping a lot of hoops to work around things as is.

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

Yes, that was fascinating stuff;-> I am still scratching my head and
continuing to itch on when i can get more time to look closely with some
testing. But i dont see the connection with what Changli is attempting
with multiq ifb - what do you have in mind.

cheers,
jamal

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