On 03/06/2013 10:48 AM, Thomas Gleixner wrote: > On Wed, 6 Mar 2013, Daniel Lezcano wrote: >> On 03/05/2013 09:40 PM, Thomas Gleixner wrote: >>> On Sat, 2 Mar 2013, Daniel Lezcano wrote: >>>> When a cpu goes to a deep idle state where its local timer is shutdown, >>>> it notifies the time frame work to use the broadcast timer instead. >>>> >>>> Unfortunately, the broadcast device could wake up any CPU, including an >>>> idle one which is not concerned by the wake up at all. >>>> >>>> This implies, in the worst case, an idle CPU will wake up to send an IPI >>>> to another idle cpu. >>>> >>>> This patch solves this by setting the irq affinity to the cpu concerned >>>> by the nearest timer event, by this way, the CPU which is wake up is >>>> guarantee to be the one concerned by the next event and we are safe with >>>> unnecessary wakeup for another idle CPU. >>>> >>>> As the irq affinity is not supported by all the archs, a flag is needed >>>> to specify which clocksource can handle it : CLOCK_EVT_FEAT_DYNIRQ >>>> >>>> Signed-off-by: Daniel Lezcano <daniel.lezc...@linaro.org> >>>> --- >>>> include/linux/clockchips.h | 5 +++++ >>>> kernel/time/tick-broadcast.c | 40 >>>> +++++++++++++++++++++++++++++++++------- >>>> 2 files changed, 38 insertions(+), 7 deletions(-) >>>> >>>> diff --git a/include/linux/clockchips.h b/include/linux/clockchips.h >>>> index 6634652..c93e2a6 100644 >>>> --- a/include/linux/clockchips.h >>>> +++ b/include/linux/clockchips.h >>>> @@ -55,6 +55,11 @@ enum clock_event_nofitiers { >>>> #define CLOCK_EVT_FEAT_C3STOP 0x000008 >>>> #define CLOCK_EVT_FEAT_DUMMY 0x000010 >>>> >>>> +/* >>>> + * Clock event device can set its irq affinity dynamically >>>> + */ >>>> +#define CLOCK_EVT_FEAT_DYNIRQ 0x000020 >>>> + >>>> /** >>>> * struct clock_event_device - clock event device descriptor >>>> * @event_handler: Assigned by the framework to be called by the >>>> low >>>> diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c >>>> index 6197ac0..9ca8ff5 100644 >>>> --- a/kernel/time/tick-broadcast.c >>>> +++ b/kernel/time/tick-broadcast.c >>>> @@ -406,13 +406,37 @@ struct cpumask *tick_get_broadcast_oneshot_mask(void) >>>> return to_cpumask(tick_broadcast_oneshot_mask); >>>> } >>>> >>>> -static int tick_broadcast_set_event(struct clock_event_device *bc, >>>> +/* >>>> + * Set broadcast interrupt affinity >>>> + */ >>>> +static void tick_broadcast_set_affinity(struct clock_event_device *bc, >>>> + const struct cpumask *cpumask) >>>> +{ >>>> + if (!(bc->features & CLOCK_EVT_FEAT_DYNIRQ)) >>>> + return; >>>> + >>>> + if (cpumask_equal(bc->cpumask, cpumask)) >>>> + return; >>>> + >>>> + bc->cpumask = cpumask; >>> >>> This breaks with CONFIG_CPUMASK_OFFSTACK=y. cpumask_copy() is your friend! >> >> This instruction copies the pointer, not the cpumask content. >> >> bc->cpumask is defined as a const struct cpumask * and is used to copy a >> cpumask pointer not the content. >> >> The cpumask parameter is a pointer to a global cpumask provided by the >> cpumask_of macro. >> >> But to be in the safe side, I compiled tested with >> CONFIG_CPUMASK_OFFSTACK=y without problem. >> >> Did I missed something ? > > No, I misinterpreted the patch. Assigning a pointer is safe.
Ok, thanks anyway for reviewing the patch. Do you think it is acceptable for upstreaming ? -- Daniel <http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs Follow Linaro: <http://www.facebook.com/pages/Linaro> Facebook | <http://twitter.com/#!/linaroorg> Twitter | <http://www.linaro.org/linaro-blog/> Blog -- 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/