Messages in this thread | | | Date | Tue, 12 Nov 2019 14:55:41 +0000 | From | Russell King - ARM Linux admin <> | Subject | Re: [PATCH] arm: kernel: initialize broadcast hrtimer based clock event device |
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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 <benjamin.gaignard@st.com> > > Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Thanks. Benjamin, please put it in the patch system, thanks.
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