linux-kernel - Re: [RFC PATCH 1/2] mac80211: make max_network

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Message-ID: <20100609173740.3851c6a5@schatten.dmk.lab>
Date:	Wed, 9 Jun 2010 17:37:40 +0200
From:	Florian Mickler <florian@...kler.org>
To:	Johannes Berg <johannes@...solutions.net>
Cc:	pm list <linux-pm@...ts.linux-foundation.org>,
	james.bottomley@...e.de, markgross@...gnar.org,
	mgross@...ux.intel.com,
	"John W. Linville" <linville@...driver.com>,
	"David S. Miller" <davem@...emloft.net>,
	Javier Cardona <javier@...ybit.com>, Jouni Malinen <j@...fi>,
	Rui Paulo <rpaulo@...il.com>,
	Kalle Valo <kalle.valo@...ia.com>,
	linux-wireless@...r.kernel.org, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC PATCH 1/2] mac80211: make max_network_latency notifier
 atomic safe

On Wed, 09 Jun 2010 14:27:05 +0200
Johannes Berg <johannes@...solutions.net> wrote:

> On Wed, 2010-06-09 at 14:16 +0200, Florian Mickler wrote:
> 
> > That was also my first idea, but then I thought about qos and thought
> > atomic notification are necessary.
> > Do you see any value in having atomic notification? 
> > 
> > I have the following situation before my eyes:
> > 
> > 	Driver A gets an interrupt and needs (to service that
> > 	interrupt) the cpu to guarantee a latency of X because the
> > 	device is a bit icky.
> > 
> > Now, in that situation, if we don't immediately (without scheduling in
> > between) notify the system to be in that latency-mode the driver won't
> > function properly. Is this a realistic scene?
> > 
> > At the moment we only have process context notification and only 2
> > listeners.
> > 
> > I think providing for atomic as well as "relaxed" notification could be
> > useful. 
> > 
> > If atomic notification is deemed unnecessary, I have no
> > problems to just use schedule_work() in update request.
> > Anyway, it is probably best to split this. I.e. first make
> > update_request callable from atomic contexts with doing the
> > schedule_work in update_request and then
> > as an add on provide for constraints_objects with atomic notifications.
> 
> Well I remember http://thread.gmane.org/gmane.linux.kernel/979935 where
> Mark renamed things to "request" which seems to imply to me more of a
> "please do this" than "I NEED IT NOW!!!!!".
> 
> johannes

Yes. I just posted a version which uses schedule_work().
Just FYI, James has also posted his version which uses either a blocking
or an atomic notifier chain.
http://article.gmane.org/gmane.linux.kernel/996813

Cheers,
Flo

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