Subject: Re: [net-next PATCH V5] qdisc: bulk dequeue support for qdiscs with TCQ_F_ONETXQUEUE

From: Jamal Hadi Salim <[email-masked]>
Date: Wed, 01 Oct 2014 14:55:09 -0400

On 10/01/14 13:28, Jesper Dangaard Brouer wrote:

> Thus, code is activated only when q->qlen is >= 1. And I have already
> shown that we see a win with just bulking 2 packets:

If you can get 2 packets, indeed you win. If you can on average get >1
over a long period, you still win.
You have clearly demonstrated you can do that with traffic
generators (udp or in kernel pktgen). I was more worried about the
common use case scenario (handwaved as 1-24 TCP streams).

The key here is: *if you never hit bulking* then the cost is
_per packet_ for sch_direct_xmit bypass.
Question is what is that cost for the common case as defined above?
Can you hit a bulk level >1 on 1-24 TCP streams?
I would be happy if your answer is *yes*. If your answer is no (since
it is hard to achieve) - then how far off is it from before your
patches (since now you have added at minimal a branch check).
I think it is fair for you to quantify that, no?
Feature is still useful for the other cases.

Note:
This is what i referred to as the "no animals were hurt during the
making of these patches" statement. I am sorry again for raining on
the parade.

cheers,
jamal