| Message ID | 1417119024-22844-3-git-send-email-daniel.thompson@linaro.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Thu, 27 Nov 2014, Daniel Thompson wrote: > Currently gic_raise_softirq() unconditionally takes and releases a lock > whose only purpose is to synchronize with the b.L switcher. > > Remove this lock if the b.L switcher is not compiled in. I think the patches are in the wrong order. We optimize for the sane use case first, i.e BL=n. So you want to make the locking of irq_controller_lock in gic_raise_softirq() conditional in the first place, which should have been done when this was introduced. Once you have isolated that you can apply your split lock patch for the BL=y nonsense. Adding more locks first and then optimizing them out does not make any sense. Thanks, tglx
On 27/11/14 21:37, Thomas Gleixner wrote: > On Thu, 27 Nov 2014, Daniel Thompson wrote: > >> Currently gic_raise_softirq() unconditionally takes and releases a lock >> whose only purpose is to synchronize with the b.L switcher. >> >> Remove this lock if the b.L switcher is not compiled in. > > I think the patches are in the wrong order. We optimize for the sane > use case first, i.e BL=n. So you want to make the locking of > irq_controller_lock in gic_raise_softirq() conditional in the first > place, which should have been done when this was introduced. > > Once you have isolated that you can apply your split lock patch for > the BL=y nonsense. > > Adding more locks first and then optimizing them out does not make any > sense. You original described the use of irq_controller_lock for its current dual purpose to be an abuse of the lock. Does it really make more sense to optimize before we correct the abuse? How about just squashing them together? It reduces the combined diffstat by ~10%... Daniel.
diff --git a/drivers/irqchip/irq-gic.c b/drivers/irqchip/irq-gic.c index 94d77118efa8..e875da93f24a 100644 --- a/drivers/irqchip/irq-gic.c +++ b/drivers/irqchip/irq-gic.c @@ -76,8 +76,23 @@ 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. */ +#ifdef CONFIG_BL_SWITCHER static DEFINE_RAW_SPINLOCK(cpu_map_migration_lock); +static inline void bl_migration_lock(unsigned long *flags) +{ + raw_spin_lock_irqsave(&cpu_map_migration_lock, *flags); +} + +static inline void bl_migration_unlock(unsigned long flags) +{ + raw_spin_unlock_irqrestore(&cpu_map_migration_lock, flags); +} +#else +static inline void bl_migration_lock(unsigned long *flags) {} +static inline void bl_migration_unlock(unsigned long flags) {} +#endif + /* * The GIC mapping of CPU interfaces does not necessarily match * the logical CPU numbering. Let's use a mapping as returned @@ -630,7 +645,7 @@ static void gic_raise_softirq(const struct cpumask *mask, unsigned int irq) int cpu; unsigned long flags, map = 0; - raw_spin_lock_irqsave(&cpu_map_migration_lock, flags); + bl_migration_lock(&flags); /* Convert our logical CPU mask into a physical one. */ for_each_cpu(cpu, mask) @@ -645,7 +660,7 @@ 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(&cpu_map_migration_lock, flags); + bl_migration_unlock(flags); } #endif
Currently gic_raise_softirq() unconditionally takes and releases a lock whose only purpose is to synchronize with the b.L switcher. Remove this lock if the b.L switcher is not compiled in. Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Jason Cooper <jason@lakedaemon.net> Cc: Russell King <linux@arm.linux.org.uk> Cc: Marc Zyngier <marc.zyngier@arm.com> --- drivers/irqchip/irq-gic.c | 19 +++++++++++++++++-- 1 file changed, 17 insertions(+), 2 deletions(-)