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Message-ID: <512D9A8F.3080305@ti.com>
Date: Wed, 27 Feb 2013 11:03:03 +0530
From: Santosh Shilimkar <santosh.shilimkar@...com>
To: Daniel Lezcano <daniel.lezcano@...aro.org>
CC: <john.stultz@...aro.org>, <tglx@...utronix.de>,
<viresh.kumar@...aro.org>, <jacob.jun.pan@...ux.intel.com>,
<linux-arm-kernel@...ts.infradead.org>, <linux-pm@...r.kernel.org>,
<linux-kernel@...r.kernel.org>, <linaro-kernel@...ts.linaro.org>,
<patches@...aro.org>, <linus.walleij@...ricsson.com>
Subject: Re: [PATCH 2/4] time : set broadcast irq affinity
On Wednesday 27 February 2013 03:47 AM, 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.
>
Minor. Can mention the flag name as well here "CLOCK_EVT_FEAT_DYNIRQ"
> Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>
> ---
> include/linux/clockchips.h | 1 +
> kernel/time/tick-broadcast.c | 39 ++++++++++++++++++++++++++++++++-------
> 2 files changed, 33 insertions(+), 7 deletions(-)
>
> diff --git a/include/linux/clockchips.h b/include/linux/clockchips.h
> index 6634652..c256cea 100644
> --- a/include/linux/clockchips.h
> +++ b/include/linux/clockchips.h
> @@ -54,6 +54,7 @@ enum clock_event_nofitiers {
> */
> #define CLOCK_EVT_FEAT_C3STOP 0x000008
> #define CLOCK_EVT_FEAT_DUMMY 0x000010
> +#define CLOCK_EVT_FEAT_DYNIRQ 0x000020
>
Please add some comments about the usage of the flag.
> /**
> * struct clock_event_device - clock event device descriptor
> diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c
> index 6197ac0..1f7b4f4 100644
> --- a/kernel/time/tick-broadcast.c
> +++ b/kernel/time/tick-broadcast.c
> @@ -406,13 +406,36 @@ 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, int cpu)
> +{
Better is just make second parameter as cpu_mask rather than CPU
cpu number. Its a semantic of affinity hook which you can easily retain.
> + if (!(bc->features & CLOCK_EVT_FEAT_DYNIRQ))
> + return;
> +
> + if (cpumask_equal(bc->cpumask, cpumask_of(cpu)))
> + return;
> +
> + bc->cpumask = cpumask_of(cpu);
You can avoid the cpumask_of() couple of times above.
> + irq_set_affinity(bc->irq, bc->cpumask);
> +}
> +
> +static int tick_broadcast_set_event(struct clock_event_device *bc, int cpu,
> ktime_t expires, int force)
> {
> + int ret;
> +
> if (bc->mode != CLOCK_EVT_MODE_ONESHOT)
> clockevents_set_mode(bc, CLOCK_EVT_MODE_ONESHOT);
>
> - return clockevents_program_event(bc, expires, force);
> + ret = clockevents_program_event(bc, expires, force);
> + if (ret)
> + return ret;
> +
> + tick_broadcast_set_affinity(bc, cpu);
In case you go by cpumask paramater, then above can be just
tick_broadcast_set_affinity(bc, cpumask_of(cpu));
> +
> + return 0;
> }
>
> int tick_resume_broadcast_oneshot(struct clock_event_device *bc)
> @@ -441,7 +464,7 @@ static void tick_handle_oneshot_broadcast(struct clock_event_device *dev)
> {
> struct tick_device *td;
> ktime_t now, next_event;
> - int cpu;
> + int cpu, next_cpu;
>
> raw_spin_lock(&tick_broadcast_lock);
> again:
> @@ -454,8 +477,10 @@ again:
> td = &per_cpu(tick_cpu_device, cpu);
> if (td->evtdev->next_event.tv64 <= now.tv64)
> cpumask_set_cpu(cpu, to_cpumask(tmpmask));
> - else if (td->evtdev->next_event.tv64 < next_event.tv64)
> + else if (td->evtdev->next_event.tv64 < next_event.tv64) {
> next_event.tv64 = td->evtdev->next_event.tv64;
> + next_cpu = cpu;
> + }
> }
>
> /*
> @@ -478,7 +503,7 @@ again:
> * Rearm the broadcast device. If event expired,
> * repeat the above
> */
> - if (tick_broadcast_set_event(dev, next_event, 0))
> + if (tick_broadcast_set_event(dev, next_cpu, next_event, 0))
> goto again;
> }
> raw_spin_unlock(&tick_broadcast_lock);
> @@ -521,7 +546,7 @@ void tick_broadcast_oneshot_control(unsigned long reason)
> cpumask_set_cpu(cpu, tick_get_broadcast_oneshot_mask());
> clockevents_set_mode(dev, CLOCK_EVT_MODE_SHUTDOWN);
> if (dev->next_event.tv64 < bc->next_event.tv64)
> - tick_broadcast_set_event(bc, dev->next_event, 1);
> + tick_broadcast_set_event(bc, cpu, dev->next_event, 1);
Since you have embedded the irq_affinity() in above function,
the IRQ affinity for bc->irq will remain to the last CPU
on which the interrupt fired. In general it should be fine
but would be good if you clear it on
CLOCK_EVT_NOTIFY_BROADCAST_EXIT. Not a must have though.
Regards,
Santosh
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