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

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Message-ID: <1276086425.14580.14.camel@jlt3.sipsolutions.net>
Date:	Wed, 09 Jun 2010 14:27:05 +0200
From:	Johannes Berg <johannes@...solutions.net>
To:	Florian Mickler <florian@...kler.org>
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, 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

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