Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752765AbbGENLY (ORCPT ); Sun, 5 Jul 2015 09:11:24 -0400 Received: from pandora.arm.linux.org.uk ([78.32.30.218]:49331 "EHLO pandora.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751141AbbGENLC (ORCPT ); Sun, 5 Jul 2015 09:11:02 -0400 Date: Sat, 4 Jul 2015 11:08:27 +0100 From: Russell King - ARM Linux To: Thomas Gleixner Cc: Jisheng Zhang , jason@lakedaemon.net, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v2 2/2] irqchip: dw-apb-ictl: add irq_set_affinity support Message-ID: <20150704100827.GC7557@n2100.arm.linux.org.uk> References: <1435987170-3962-1-git-send-email-jszhang@marvell.com> <1435987170-3962-3-git-send-email-jszhang@marvell.com> <20150704082623.GA7557@n2100.arm.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1902 Lines: 41 On Sat, Jul 04, 2015 at 11:53:57AM +0200, Thomas Gleixner wrote: > On Sat, 4 Jul 2015, Russell King - ARM Linux wrote: > > > On Sat, Jul 04, 2015 at 01:19:30PM +0800, Jisheng Zhang wrote: > > > On Marvell Berlin SoCs, the cpu's local timer is shutdown when the cpu > > > goes to a deep idle state, then the timer framework will be notified to > > > use a broadcast timer instead. The broadcast timer uses dw-apb-ictl as > > > interrupt chip, this patch adds irq_set_affinity support so that the > > > going to deep idle state cpu can set the interrupt affinity of the > > > broadcast interrupt to avoid unnecessary wakeups and IPIs. > > > > NAK to this patch. > > > > The real question is - if CPU0 is the CPU going offline, why is it > > still receiving _any_ interrupts - all interrupts should be migrated > > off it, including the chained interrupts. > > > > Sounds like there's a bug in the migration code which needs further > > investigation, rather than hacking around the problem by introducing > > lots of driver code. > > I think you misunderstood the changelog, which is horrible btw. > > So the real reason to do this is to steer the broadcast interrupt to > the CPU which has the earliest expiry time. This avoids that another > cpu is woken from idle just to deliver the broadcast IPI to the other > cpu. Unless I'm mistaken, the code does this by messing around with the parent interrupt affinity of a chained interrupt, which really isn't a good thing to do, because it migrates every interrupt on the child interrupt controller. -- FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up according to speedtest.net. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/