netdev - Re: [PATCH 1/4] [NET_SCHED] explict hold dev tx lock

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Date:	Tue, 25 Sep 2007 09:15:38 -0400
From:	jamal <hadi@...erus.ca>
To:	Stephen Hemminger <shemminger@...ux-foundation.org>
Cc:	"Waskiewicz Jr, Peter P" <peter.p.waskiewicz.jr@...el.com>,
	David Miller <davem@...emloft.net>, krkumar2@...ibm.com,
	johnpol@....mipt.ru, herbert@...dor.apana.org.au, kaber@...sh.net,
	jagana@...ibm.com, Robert.Olsson@...a.slu.se, rick.jones2@...com,
	xma@...ibm.com, gaagaan@...il.com, netdev@...r.kernel.org,
	rdreier@...co.com, mcarlson@...adcom.com, jeff@...zik.org,
	mchan@...adcom.com, general@...ts.openfabrics.org,
	kumarkr@...ux.ibm.com, tgraf@...g.ch, randy.dunlap@...cle.com,
	sri@...ibm.com
Subject: Re: [PATCH 1/4] [NET_SCHED] explict hold dev tx lock

On Mon, 2007-24-09 at 17:14 -0700, Stephen Hemminger wrote:

> Since we are redoing this, 
> is there any way to make the whole TX path
> more lockless?  The existing model seems to be more of a monitor than
> a real locking model.

What do you mean it is "more of a monitor"?

On the challenge of making it lockless:
About every NAPI driver combines the tx prunning with rx polling. If you
are dealing with tx resources on receive thread as well as tx thread,
_you need_ locking. The only other way we can do avoid it is to separate
the rx path interupts from ones on tx related resources; the last NAPI
driver that did that was tulip; i think the e1000 for a short period in
its life did the same as well. But that has been frowned on and people
have evolved away from it.

cheers,
jamal

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