netdev - Re: [net-next PATCH 1/1 V4] qdisc: bulk dequeue support for qdiscs with TCQ_F

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Date:	Thu, 25 Sep 2014 08:58:54 -0700
From:	Tom Herbert <therbert@...gle.com>
To:	Jesper Dangaard Brouer <brouer@...hat.com>
Cc:	Jamal Hadi Salim <jhs@...atatu.com>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Linux Netdev List <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Alexander Duyck <alexander.h.duyck@...el.com>,
	Toke Høiland-Jørgensen <toke@...e.dk>,
	Florian Westphal <fw@...len.de>,
	Dave Taht <dave.taht@...il.com>,
	John Fastabend <john.r.fastabend@...el.com>,
	Daniel Borkmann <dborkman@...hat.com>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>
Subject: Re: [net-next PATCH 1/1 V4] qdisc: bulk dequeue support for qdiscs
 with TCQ_F_ONETXQUEUE

On Thu, Sep 25, 2014 at 8:23 AM, Jesper Dangaard Brouer
<brouer@...hat.com> wrote:
> On Thu, 25 Sep 2014 08:05:38 -0700
> Tom Herbert <therbert@...gle.com> wrote:
>
>> On Thu, Sep 25, 2014 at 7:57 AM, Jesper Dangaard Brouer
>> <brouer@...hat.com> wrote:
>> > On Thu, 25 Sep 2014 07:40:33 -0700
>> > Tom Herbert <therbert@...gle.com> wrote:
>> >
>> >> A few test results in patch 0 are good. I like to have results for
>> >> with and without patch. These should two things: 1) Any regressions
>> >> caused by the patch 2) Performance gains (in that order of importance
>> >> :-) ). There doesn't need to be a lot here, just something reasonably
>> >> representative, simple, and should be easily reproducible. My
>> >> expectation in bulk dequeue is that we should see no obvious
>> >> regression and hopefully an improvement in CPU utilization-- are you
>> >> able to verify this?
>> >
>> > We are saving 3% CPU, as I described in my post with subject:
>> > "qdisc/UDP_STREAM: measuring effect of qdisc bulk dequeue":
>> >  http://thread.gmane.org/gmane.linux.network/331152/focus=331154
>> >
>> > Using UDP_STREAM on 1Gbit/s driver igb, I can show that the
>> > _raw_spin_lock calls are reduced with approx 3%, when enabling
>> > bulking of just 2 packets.
>> >
>>
>> That's great. In commit log, would be good to have results with
>> TCP_STREAM also and please report aggregate CPU utilization changes
>> (like from mpstat).
>
> The TCP_STREAM is not a good test for this, because unless disabling
> both TSO and GSO the packets will not hit the code path (that this
> patch changes).  When we later add support for TSO and GSO bulking,
> then it will make sense to include TCP_STREAM testing, not before.
>
Disabling TSO and GSO is fine. I'm interested to see interactions with TCP.

> I will redo the tests, once I get home to my testlab, as the remote lab
> I'm using now is annoyingly slow rebooting machines, as we not longer
> have a runtime option for enable/disable (I'm currently in Switzerland).
>
> --
> 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
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