From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 97C23C43331 for ; Tue, 12 Nov 2019 14:56:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 40AC420656 for ; Tue, 12 Nov 2019 14:56:05 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=armlinux.org.uk header.i=@armlinux.org.uk header.b="Ah4mAq6x" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727074AbfKLO4E (ORCPT ); Tue, 12 Nov 2019 09:56:04 -0500 Received: from pandora.armlinux.org.uk ([78.32.30.218]:53616 "EHLO pandora.armlinux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726484AbfKLO4D (ORCPT ); Tue, 12 Nov 2019 09:56:03 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=armlinux.org.uk; s=pandora-2019; h=Sender:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=CC6CDOjq53lam0n3yDiGEmY1dG4I1rOGEfq4W7Fmwjw=; b=Ah4mAq6xeMy0RJp4jo/JkpuRf 8hfsp1qtuvNn+wWx+lc6z+YAcUxqHvrqbqBkYnd0Vhpffd5Ooy3oI9PmOFUFwAMf2MCZ0E8bkKWVy qnql9BefveI2ESRbHqnV5FTIPK5//sb8dTaZDdyOdrr2NweIC/cfBF3c3k4NmRMVy3Yh4TaQmWYU3 PcyMMv5qmWCXrjX9FkzlbLHIkSXCfMGRlPEsfq7/069xjqRVs79HJXIZ596SjfcGMgnFloIR3WDZQ N4FzaSiG2ev1S5TbOdBMSyg6WDvC7yDskKCTdHP02N6XRAFDBqw3fl9IQGZXvOsHaZn/7Inls3ms/ A7jqS2qhg==; Received: from shell.armlinux.org.uk ([fd8f:7570:feb6:1:5054:ff:fe00:4ec]:38692) by pandora.armlinux.org.uk with esmtpsa (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.90_1) (envelope-from ) id 1iUXaC-0006Gb-1Q; Tue, 12 Nov 2019 14:55:52 +0000 Received: from linux by shell.armlinux.org.uk with local (Exim 4.92) (envelope-from ) id 1iUXa1-0001Td-TE; Tue, 12 Nov 2019 14:55:41 +0000 Date: Tue, 12 Nov 2019 14:55:41 +0000 From: Russell King - ARM Linux admin To: Thomas Gleixner Cc: Benjamin Gaignard , gregkh@linuxfoundation.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-stm32@st-md-mailman.stormreply.com Subject: Re: [PATCH] arm: kernel: initialize broadcast hrtimer based clock event device Message-ID: <20191112145541.GK25745@shell.armlinux.org.uk> References: <20191112120625.20173-1-benjamin.gaignard@st.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Nov 12, 2019 at 03:48:10PM +0100, Thomas Gleixner wrote: > On Tue, 12 Nov 2019, Benjamin Gaignard wrote: > > > On platforms implementing CPU power management, the CPUidle subsystem > > can allow CPUs to enter idle states where local timers logic is lost on power > > down. To keep the software timers functional the kernel relies on an > > always-on broadcast timer to be present in the platform to relay the > > interrupt signalling the timer expiries. > > > > For platforms implementing CPU core gating that do not implement an always-on > > HW timer or implement it in a broken way, this patch adds code to initialize > > the kernel hrtimer based clock event device upon boot (which can be chosen as > > tick broadcast device by the kernel). > > It relies on a dynamically chosen CPU to be always powered-up. This CPU then > > relays the timer interrupt to CPUs in deep-idle states through its HW local > > timer device. > > > > Having a CPU always-on has implications on power management platform > > capabilities and makes CPUidle suboptimal, since at least a CPU is kept > > always in a shallow idle state by the kernel to relay timer interrupts, > > but at least leaves the kernel with a functional system with some working > > power management capabilities. > > > > The hrtimer based clock event device is unconditionally registered, but > > has the lowest possible rating such that any broadcast-capable HW clock > > event device present will be chosen in preference as the tick broadcast > > device. > > > > Signed-off-by: Benjamin Gaignard > > Reviewed-by: Thomas Gleixner Thanks. Benjamin, please put it in the patch system, thanks. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up According to speedtest.net: 11.9Mbps down 500kbps up