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 software broadcast hrtimer upon boot. 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. On systems with power management capabilities but no functional HW broadcast tick device, the hrtimer based clock event device allows the kernel to enter high-resolution timer mode, which improves system latencies and saves dynamic power. The side effect of 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 has lowest possible rating so that, if a platform contains a functional HW clock event device with broadcast capabilities, that device is always chosen as a tick broadcast device instead of the software based one, now present by default. Cc: Preeti U Murthy <pre...@linux.vnet.ibm.com> Cc: Will Deacon <will.dea...@arm.com> Acked-by: Mark Rutland <mark.rutl...@arm.com> Signed-off-by: Lorenzo Pieralisi <lorenzo.pieral...@arm.com> --- arch/arm64/kernel/time.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/arch/arm64/kernel/time.c b/arch/arm64/kernel/time.c index 29c39d5..3d43900 100644 --- a/arch/arm64/kernel/time.c +++ b/arch/arm64/kernel/time.c @@ -18,6 +18,7 @@ * along with this program. If not, see <http://www.gnu.org/licenses/>. */ +#include <linux/clockchips.h> #include <linux/export.h> #include <linux/kernel.h> #include <linux/interrupt.h> @@ -67,6 +68,8 @@ void __init time_init(void) clocksource_of_init(); + tick_setup_hrtimer_broadcast(); + arch_timer_rate = arch_timer_get_rate(); if (!arch_timer_rate) panic("Unable to initialise architected timer.\n"); -- 1.8.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/