| Message ID | 1401383814-22600-1-git-send-email-lorenzo.pieralisi@arm.com |
|---|---|
| State | Accepted |
| Commit | 9358d755bd5cba8965ea79f2a446e689323409f9 |
| Headers | show |
On 05/29/2014 10:46 PM, Lorenzo Pieralisi 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. > > Cc: Preeti U Murthy <preeti@linux.vnet.ibm.com> > Acked-by: Will Deacon <will.deacon@arm.com> > Acked-by: Mark Rutland <mark.rutland@arm.com> > Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com> > --- > changes in v2: > > - Reworded the commit log according to reviews > > It should be ready to go. > > Thanks, > Lorenzo > > 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 6815987..1a7125c 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> > @@ -69,6 +70,8 @@ void __init time_init(void) > of_clk_init(NULL); > 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"); > Reviewed-by: Preeti U Murthy <preeti@linux.vnet.ibm.com> -- 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/
diff --git a/arch/arm64/kernel/time.c b/arch/arm64/kernel/time.c index 6815987..1a7125c 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> @@ -69,6 +70,8 @@ void __init time_init(void) of_clk_init(NULL); 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");