Messages in this thread Patch in this message | | | Date | Mon, 8 Dec 2014 10:48:29 +0000 | From | Mark Rutland <> | Subject | Re: [PATCH V2] tick-broadcast: Register for hrtimer based broadcast as the fallback broadcast mode |
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Hi Preeti,
On Mon, Dec 08, 2014 at 06:55:43AM +0000, Preeti U Murthy wrote: > Commit 5d1638acb9f6 ('tick: Introduce hrtimer based broadcast') added a > hrtimer based broadcast mode for those platforms in which local timers stop > when CPUs enter deep idle states. The commit expected the platforms to > register for this mode explicitly when they lacked a better external device > to wake up CPUs in deep idle. Given that more platforms are beginning to use > this mode, we can avoid the call to set it up on every platform that requires > it, by registering for the hrtimer based broadcast mode in the core code if > no better broadcast device is available. > > This commit also helps detect cases where the platform fails to register for > a broadcast device but invokes the help of one when entering deep idle states. > Currently we do not handle this situation at all and call the broadcast clock > device without checking for its existence. This patch will handle such buggy > cases properly. > > Signed-off-by: Preeti U Murthy <preeti@linux.vnet.ibm.com>
I've just given this a go on an arm64 platform (Juno) without any system-wide clock_event_devices registered, and everything works well with CPUs entering and exiting idle states where the cpu-local timers lose state. So:
Tested-by: Mark Rutland <mark.rutland@arm.com>
One minor thing I noticed when testing was that /sys/devices/system/clockevents/broadcast/name contained "(null)", because we never set the name field on the clock_event_device. It's always been that way, but now might be a good time to change that to something like "broadcast_hrtimer".
[...]
> diff --git a/include/linux/clockchips.h b/include/linux/clockchips.h > index 2e4cb67..91754b0 100644 > --- a/include/linux/clockchips.h > +++ b/include/linux/clockchips.h > @@ -187,11 +187,11 @@ extern int tick_receive_broadcast(void); > #endif > > #if defined(CONFIG_GENERIC_CLOCKEVENTS_BROADCAST) && defined(CONFIG_TICK_ONESHOT) > -extern void tick_setup_hrtimer_broadcast(void); > +extern int __init tick_setup_hrtimer_broadcast(void); > extern int tick_check_broadcast_expired(void); > #else > static inline int tick_check_broadcast_expired(void) { return 0; } > -static inline void tick_setup_hrtimer_broadcast(void) {}; > +static inline int __init tick_setup_hrtimer_broadcast(void) { return 0; } > #endif > > #ifdef CONFIG_GENERIC_CLOCKEVENTS > @@ -207,7 +207,7 @@ static inline void clockevents_resume(void) {} > > static inline int clockevents_notify(unsigned long reason, void *arg) { return 0; } > static inline int tick_check_broadcast_expired(void) { return 0; } > -static inline void tick_setup_hrtimer_broadcast(void) {}; > +static inline int __init tick_setup_hrtimer_broadcast(void) { return 0; }
With the initcall moved to the driver we have no external users of tick_setup_hrtimer_broadcast, so I think we can remove the prototype entirely from clockchips.h...
> #endif > > diff --git a/kernel/time/tick-broadcast-hrtimer.c b/kernel/time/tick-broadcast-hrtimer.c > index eb682d5..5c35995 100644 > --- a/kernel/time/tick-broadcast-hrtimer.c > +++ b/kernel/time/tick-broadcast-hrtimer.c > @@ -98,9 +98,11 @@ static enum hrtimer_restart bc_handler(struct hrtimer *t) > return HRTIMER_RESTART; > } > > -void tick_setup_hrtimer_broadcast(void) > +int __init tick_setup_hrtimer_broadcast(void)
...and make it static here.
> { > hrtimer_init(&bctimer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS); > bctimer.function = bc_handler; > clockevents_register_device(&ce_broadcast_hrtimer); > + return 0; > } > +early_initcall(tick_setup_hrtimer_broadcast);
Otherwise this looks good to me, thanks for putting this together!
Mark.
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