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SubjectRe: [PATCH 2/4][V2] time : set broadcast irq affinity
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.lezcano@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!

Thanks,

tglx


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