On 25/11/14 17:40, Marc Zyngier wrote: > 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.
Will do. > 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 >> > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
