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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 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-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20191112_065614_632844_3254F94B X-CRM114-Status: GOOD ( 17.67 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: gregkh@linuxfoundation.org, linux-stm32@st-md-mailman.stormreply.com, Benjamin Gaignard , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.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 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel