Messages in this thread | | | Date | Wed, 6 Mar 2013 10:48:08 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: [PATCH 2/4][V2] time : set broadcast irq affinity |
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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.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! > > 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.
Thanks,
tglx
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