From: Jesper Dangaard Brouer <brouer@redhat.com>
To: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: john Fastabend <john.r.fastabend@intel.com>,
Herbert Xu <herbert@gondor.apana.org.au>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
eric Dumazet <edumazet@google.com>,
brouer@redhat.com,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Subject: Re: qdisc running
Date: Mon, 20 Oct 2014 18:17:56 +0200 [thread overview]
Message-ID: <20141020181756.2c8f33b9@redhat.com> (raw)
In-Reply-To: <54440FFA.40307@mojatatu.com>
On Sun, 19 Oct 2014 15:24:42 -0400 Jamal Hadi Salim <jhs@mojatatu.com> wrote:
> Jesper,
>
> You asked at the meeting the point to qdisc running.
Talking about __QDISC___STATE_RUNNING see slide 9/16:
http://people.netfilter.org/hawk/presentations/LinuxPlumbers2014/performance_tx_qdisc_bulk_LPC2014.pdf
> Original intent is to allow only one cpu to enter the lower half of the
> qdisc path. IOW, if one cpu was already in the qdisc then that guy
> could be used to dequeue packets. i.e this is good for batching.
> Original idea was Herbert's with major improvement from Eric
> and a small one from me.
I guess it is good for our recent dequeue batching. But I think/hope we
can come up with a scheme that does not requires 6 lock/unlock
operations (as illustrated on slide 9).
John and I have talked about doing a lockless qdisc, but maintaining
this __QDISC___STATE_RUNNING in a lockless scenario, would cost us
extra atomic ops...
Are we still sure, that this model of only allowing a single CPU in the
dequeue path, is still the best solution? (The TXQ lock should already
protect several CPUs in this code path).
> For history of different tried approaches look at:
> Look at slide 2:
> http://vger.kernel.org/netconf2011_slides/jamal_netconf2011.pdf
I can see that you really needed the budget/fairness in the dequeue
loop, that we recently mangled with.
> then download the **amazing** flash animations which describe
> that history.
> http://vger.kernel.org/netconf2011_slides/netconf-2011-flash.tgz
>
> Follow the bullets in slide2 and map to the flash animations.
What tool do I use to play these SWF files? (I tried VLC but no luck).
> If you go over them, you'll see it is still needed.
Too bad, I would like to avoid the second
> I think someone oughta put those **amazing** animations on some
> website;->
I hope someone else can pick that up ;-)
--
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
next prev parent reply other threads:[~2014-10-20 16:18 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-10-19 19:24 qdisc running Jamal Hadi Salim
2014-10-20 16:17 ` Jesper Dangaard Brouer [this message]
2014-10-20 22:17 ` Jamal Hadi Salim
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