[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20141001192840.5679a671@redhat.com>
Date: Wed, 1 Oct 2014 19:28:40 +0200
From: Jesper Dangaard Brouer <brouer@...hat.com>
To: Jamal Hadi Salim <jhs@...atatu.com>
Cc: Tom Herbert <therbert@...gle.com>,
David Miller <davem@...emloft.net>,
Linux Netdev List <netdev@...r.kernel.org>,
Eric Dumazet <eric.dumazet@...il.com>,
Hannes Frederic Sowa <hannes@...essinduktion.org>,
Florian Westphal <fw@...len.de>,
Daniel Borkmann <dborkman@...hat.com>,
Alexander Duyck <alexander.duyck@...il.com>,
John Fastabend <john.r.fastabend@...el.com>,
Dave Taht <dave.taht@...il.com>,
Toke Høiland-Jørgensen
<toke@...e.dk>, brouer@...hat.com
Subject: Re: [net-next PATCH V5] qdisc: bulk dequeue support for qdiscs with
TCQ_F_ONETXQUEUE
On Wed, 01 Oct 2014 11:34:55 -0400 Jamal Hadi Salim <jhs@...atatu.com> wrote:
> The issue is: if i am going to attempt to do a bulk transfer
> every single time (with new code) and for the common use case the
> result is "no need to do bulking" then you just added extra code that
> is unnecessary for that common case.
> Even a single extra if statement at high packet rate is still
> costly and would be easy to observe.
[...]
>
> That is if the added code ends up being hit
> meaningfully. Jesper said (and it was my experience as well)
> that it was _hard_ to achieve bulking in such a case.
Let me close this one...
The bulk dequeue code *is* being hit meaningfully. It is _only_ going
to be activated when (q->qlen > 0) see __dev_xmit_skb() in dev.c.
When there is no queue pfifo_fast is allowed to directly call
sch_direct_xmit() without a enqueue/dequeue cycle. Thus, this code
would not be hit for every packet.
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:
"Subject: qdisc/UDP_STREAM: measuring effect of qdisc bulk dequeue"
http://thread.gmane.org/gmane.linux.network/331152/focus=331154
I actually believe, that I have already measured and shown that going
though the bulk dequeue is a win, this should show direct_xmit vs.
bulking:
"Subject: qdisc/trafgen: Measuring effect of qdisc bulk dequeue, with trafgen"
http://thread.gmane.org/gmane.linux.network/331152
--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Sr. Network Kernel Developer at Red Hat
Author of http://www.iptv-analyzer.org
LinkedIn: http://www.linkedin.com/in/brouer
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Powered by blists - more mailing lists