From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751875AbcAEJoM (ORCPT ); Tue, 5 Jan 2016 04:44:12 -0500 Received: from www.linutronix.de ([62.245.132.108]:58302 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751456AbcAEJoI (ORCPT ); Tue, 5 Jan 2016 04:44:08 -0500 Date: Tue, 5 Jan 2016 10:42:57 +0100 (CET) From: Thomas Gleixner To: Russell King - ARM Linux cc: Arnd Bergmann , LAK , Huan Wang , "mark.rutland@arm.com" , "linux-kernel@vger.kernel.org" , Huan Wang , Daniel Lezcano , John Stultz Subject: Re: [PATCH] arm: kernel: utilize hrtimer based broadcast In-Reply-To: <20160102102955.GP8644@n2100.arm.linux.org.uk> Message-ID: References: <1437124312-44700-1-git-send-email-b18965@freescale.com> <20151027081834.GB1425@svinekod> <4875455.lvoc6XpkZc@wuerfel> <20160102102955.GP8644@n2100.arm.linux.org.uk> User-Agent: Alpine 2.11 (DEB 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 2 Jan 2016, Russell King - ARM Linux wrote: > On Tue, Dec 29, 2015 at 02:54:10PM +0100, Thomas Gleixner wrote: > > I have no real opinion about that patch. It does no harm to unconditionally > > setup the hrtimer based broadcast even if it's never used. > > > > Up to the arch maintainer to decide. > > That's really not fair to keep shovelling these kinds of decisions onto > architecture maintainers without any kind of explanation about how an > architecture maintainer should make such a decision. > > Do I roll a 6-face dice, and if it gives an odd number, I apply this > patch, otherwise I reject it? > > Is there a technical basis for making the decision? If so, please > explain what the technical arguments are against having or not having > this change. The hrtimer based broadcast device is used when you have per cpu timers which stop in deeper power states, but you have no other timer hardware on the chip which can backup the per cpu timer in deep power states. The trick is that it emulates a timer hardware via a hrtimer and then tells the cpu idle code not to go into deep power states on the cpu which owns that hrtimer. All other cpus can go as deep as they want and still get woken up. The only downside of adding this unconditionally is extra code in case that it is not needed on a particular platform. Hope that helps. tglx