From: Herbert Xu <herbert@gondor.apana.org.au>
Date: Thu, 11 Sep 2008 21:00:35 +1000

On Thu, Sep 11, 2008 at 03:49:55AM -0700, David Miller wrote:

quoted

Well some kind of check has to be there.

I _did_ remove it during my initial implementation, and that
turned into a reported performance regression.

I see.  How about looking at the queue that the head-of-qdisc
packet maps to? That should be fairly cheap to compute.

This gets us back to the whole qdisc->ops->peek() discussion :)

And we don't have the qdisc lock here, taking it is undesirable,
and if we do take it we have to transfer that lock down into
__qdisc_run() which means adjusting all the other __qdisc_run()
callers.

It's very clumsy at best.

I therefore don't think it's wise peeking into the qdisc here.

But I do realize we have to do something about this, hmmm...