netdev - Re: [RFC] [PATCH] Don't run __qdisc

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Message-ID: <OF414D73BF.FAE11563-ON65257602.0047D9A4-65257602.00483330@in.ibm.com>
Date:	Wed, 29 Jul 2009 18:38:36 +0530
From:	Krishna Kumar2 <krkumar2@...ibm.com>
To:	Jarek Poplawski <jarkao2@...il.com>
Cc:	David Miller <davem@...emloft.net>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	netdev@...r.kernel.org
Subject: Re: [RFC] [PATCH] Don't run __qdisc_run() on a stopped TX queue

Hi Jarek,

Jarek Poplawski <jarkao2@...il.com> wrote on 07/29/2009 06:17:34 PM:

> Re: [RFC] [PATCH] Don't run __qdisc_run() on a stopped TX queue
>
> On Wed, Jul 29, 2009 at 08:30:41PM +0800, Herbert Xu wrote:
> > On Wed, Jul 29, 2009 at 11:26:14AM +0000, Jarek Poplawski wrote:
> > >
> > > If you mean the tx lock there should be no "real" contention: only
> > > one waiter max. qdisc lock's contention might be higher, but it's
> > > use (during contention) better: enqueue + dequeue together instead
> > > of doing it separately.
> >
> > Hmm, you will have contention if they're both transmitting a
> > single flow which must always go into a single physical queue.
> >
> > So you'll have two CPUs doing the work of a single CPU, with one
> > of them always spinning on the TX lock.
>
> Hmm.. I'd call it a little waiting, but OK let's call it contention;-)
> When tx is faster than queue operations there could be no contention
> at all. I'm not saying I must be right: IMHO it's only worth trying.

My expectation is that tx would be much longer than a few lines of
queue operation....

thanks,

- KK

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