Hi Daniel,
On 25/11/14 17:26, Daniel Thompson wrote:
> irq_controller_lock is used for multiple purposes within the gic driver.
> Primarily it is used to make register read-modify-write sequences atomic.
> It is also used by gic_raise_softirq() in order that the big.LITTLE
> migration logic can figure out when it is safe to migrate interrupts
> between physical cores.
>
> The second usage of irq_controller_lock is difficult to discern when
> reviewing the code because the migration itself takes place outside
> the lock.
>
> This patch makes the second usage more explicit by splitting it out into
> a separate lock and providing better comments.
While we're at it, how about an additional patch that would make this
lock disappear entirely when the big-little stuff is not compiled in,
which is likely to be the case on a lot of (dare I say most?) systems?
That will save expensive barriers that we definitely could do without.
It otherwise looks good to me.
Thanks,
M.
> Signed-off-by: Daniel Thompson <[email protected]>
> Cc: Thomas Gleixner <[email protected]>
> Cc: Jason Cooper <[email protected]>
> Cc: Russell King <[email protected]>
> Cc: Marc Zyngier <[email protected]>
> ---
> drivers/irqchip/irq-gic.c | 21 ++++++++++++++++++---
> 1 file changed, 18 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/irqchip/irq-gic.c b/drivers/irqchip/irq-gic.c
> index 38493ff28fa5..bb4bc20573ea 100644
> --- a/drivers/irqchip/irq-gic.c
> +++ b/drivers/irqchip/irq-gic.c
> @@ -73,6 +73,12 @@ struct gic_chip_data {
> static DEFINE_RAW_SPINLOCK(irq_controller_lock);
>
> /*
> + * This lock is used by the big.LITTLE migration code to ensure no
> + * IPIs can be pended on the old core after the map has been updated.
> + */
> +static DEFINE_RAW_SPINLOCK(cpu_map_migration_lock);
> +
> +/*
> * The GIC mapping of CPU interfaces does not necessarily match
> * the logical CPU numbering. Let's use a mapping as returned
> * by the GIC itself.
> @@ -624,7 +630,7 @@ static void gic_raise_softirq(const struct cpumask *mask,
> unsigned int irq)
> int cpu;
> unsigned long flags, map = 0;
>
> - raw_spin_lock_irqsave(&irq_controller_lock, flags);
> + raw_spin_lock_irqsave(&cpu_map_migration_lock, flags);
>
> /* Convert our logical CPU mask into a physical one. */
> for_each_cpu(cpu, mask)
> @@ -639,7 +645,7 @@ static void gic_raise_softirq(const struct cpumask *mask,
> unsigned int irq)
> /* this always happens on GIC0 */
> writel_relaxed(map << 16 | irq, gic_data_dist_base(&gic_data[0]) +
> GIC_DIST_SOFTINT);
>
> - raw_spin_unlock_irqrestore(&irq_controller_lock, flags);
> + raw_spin_unlock_irqrestore(&cpu_map_migration_lock, flags);
> }
> #endif
>
> @@ -710,8 +716,17 @@ void gic_migrate_target(unsigned int new_cpu_id)
>
> raw_spin_lock(&irq_controller_lock);
>
> - /* Update the target interface for this logical CPU */
> + /*
> + * Update the target interface for this logical CPU
> + *
> + * From the point we release the cpu_map_migration_lock any new
> + * SGIs will be pended on the new cpu which makes the set of SGIs
> + * pending on the old cpu static. That means we can defer the
> + * migration until after we have released the irq_controller_lock.
> + */
> + raw_spin_lock(&cpu_map_migration_lock);
> gic_cpu_map[cpu] = 1 << new_cpu_id;
> + raw_spin_unlock(&cpu_map_migration_lock);
>
> /*
> * Find all the peripheral interrupts targetting the current
>
--
Jazz is not dead. It just smells funny...
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