Now that we've removed the rq->lock requirement from the first part of ttwu() and can compute placement without holding any rq->lock, ensure we execute the second half of ttwu() on the actual cpu we want the task to run on. This avoids having to take rq->lock and doing the task enqueue remotely, saving lots on cacheline transfers. As measured using: http://oss.oracle.com/~mason/sembench.c $ echo 4096 32000 64 128 > /proc/sys/kernel/sem $ ./sembench -t 2048 -w 1900 -o 0 unpatched: run time 30 seconds 537953 worker burns per second patched: run time 30 seconds 657336 worker burns per second Still need to sort out all the races marked XXX (non-trivial), and its x86 only for the moment. Signed-off-by: Peter Zijlstra --- arch/x86/kernel/smp.c | 1 include/linux/sched.h | 2 kernel/sched.c | 143 ++++++++++++++++++++++++++++++++++++------------ kernel/sched_features.h | 2 4 files changed, 114 insertions(+), 34 deletions(-) Index: linux-2.6/arch/x86/kernel/smp.c =================================================================== --- linux-2.6.orig/arch/x86/kernel/smp.c +++ linux-2.6/arch/x86/kernel/smp.c @@ -205,6 +205,7 @@ void smp_reschedule_interrupt(struct pt_ /* * KVM uses this interrupt to force a cpu out of guest mode */ + sched_ttwu_pending(); } void smp_call_function_interrupt(struct pt_regs *regs) Index: linux-2.6/include/linux/sched.h =================================================================== --- linux-2.6.orig/include/linux/sched.h +++ linux-2.6/include/linux/sched.h @@ -1020,6 +1020,7 @@ partition_sched_domains(int ndoms_new, c } #endif /* !CONFIG_SMP */ +void sched_ttwu_pending(void); struct io_context; /* See blkdev.h */ @@ -1201,6 +1202,7 @@ struct task_struct { int lock_depth; /* BKL lock depth */ #ifdef CONFIG_SMP + struct task_struct *wake_entry; int on_cpu; #endif int on_rq; Index: linux-2.6/kernel/sched.c =================================================================== --- linux-2.6.orig/kernel/sched.c +++ linux-2.6/kernel/sched.c @@ -559,6 +559,10 @@ struct rq { /* BKL stats */ unsigned int bkl_count; #endif + +#ifdef CONFIG_SMP + struct task_struct *wake_list; +#endif }; static DEFINE_PER_CPU_SHARED_ALIGNED(struct rq, runqueues); @@ -2429,6 +2433,100 @@ ttwu_do_wakeup(struct rq *rq, struct tas wq_worker_waking_up(p, cpu_of(rq)); } +static void +ttwu_do_activate(struct rq *rq, struct task_struct *p, int wake_flags) +{ +#ifdef CONFIG_SMP + if (task_cpu(p) != cpu_of(rq)) + set_task_cpu(p, cpu_of(rq)); +#endif + + if (p->sched_contributes_to_load) + rq->nr_uninterruptible--; + + activate_task(rq, p, ENQUEUE_WAKEUP | ENQUEUE_WAKING); + ttwu_do_wakeup(rq, p, wake_flags); +} + +/* + * Called in case the task @p isn't fully descheduled from its runqueue, + * in this case we must do a remote wakeup. Its a 'light' wakeup though, + * since all we need to do is flip p->state to TASK_RUNNING, since + * the task is still ->on_rq. + */ +static int ttwu_remote(struct task_struct *p, int wake_flags) +{ + struct rq *rq; + int ret = 0; + + rq = __task_rq_lock(p); + if (p->on_rq) { + ttwu_do_wakeup(rq, p, wake_flags); + ttwu_stat(p, task_cpu(p), wake_flags); + ret = 1; + } + __task_rq_unlock(rq); + + return ret; +} + +void sched_ttwu_pending(void) +{ +#ifdef CONFIG_SMP + struct rq *rq = this_rq(); + struct task_struct *list = xchg(&rq->wake_list, NULL); + + if (!list) + return; + + raw_spin_lock(&rq->lock); + + while (list) { + struct task_struct *p = list; + list = list->wake_entry; + ttwu_do_activate(rq, p, 0); + } + + raw_spin_unlock(&rq->lock); +#endif +} + +#ifdef CONFIG_SMP +static void ttwu_queue_remote(struct task_struct *p, int cpu) +{ + struct task_struct *next = NULL; + struct rq *rq = cpu_rq(cpu); + + for (;;) { + struct task_struct *old = next; + + p->wake_entry = next; + next = cmpxchg(&rq->wake_list, old, p); + if (next == old) + break; + } + + if (!next) + smp_send_reschedule(cpu); +} +#endif + +static void ttwu_queue(struct task_struct *p, int cpu) +{ + struct rq *rq = cpu_rq(cpu); + +#ifdef CONFIG_SMP + if (!sched_feat(TTWU_FORCE_REMOTE) && cpu != smp_processor_id()) { + ttwu_queue_remote(p, cpu); + return; + } +#endif + + raw_spin_lock(&rq->lock); + ttwu_do_activate(rq, p, 0); + raw_spin_unlock(&rq->lock); +} + /** * try_to_wake_up - wake up a thread * @p: the thread to be awakened @@ -2447,29 +2545,18 @@ ttwu_do_wakeup(struct rq *rq, struct tas static int try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags) { - int cpu, this_cpu, success = 0; unsigned long flags; - struct rq *rq; - - this_cpu = get_cpu(); + int cpu, success = 0; smp_wmb(); raw_spin_lock_irqsave(&p->pi_lock, flags); if (!(p->state & state)) goto out; - cpu = task_cpu(p); - - if (p->on_rq) { - rq = __task_rq_lock(p); - if (p->on_rq) - goto out_running; - __task_rq_unlock(rq); - } + success = 1; /* we're going to change ->state */ -#ifdef CONFIG_SMP - while (p->on_cpu) - cpu_relax(); + if (p->on_rq && ttwu_remote(p, wake_flags)) + goto out; p->sched_contributes_to_load = !!task_contributes_to_load(p); p->state = TASK_WAKING; @@ -2482,7 +2569,12 @@ try_to_wake_up(struct task_struct *p, un * their feet. */ smp_mb(); - raw_spin_unlock_wait(&task_rq(p)->lock); + cpu = task_cpu(p); + raw_spin_unlock_wait(&cpu_rq(cpu)->lock); + +#ifdef CONFIG_SMP + while (p->on_cpu) + cpu_relax(); if (p->sched_class->task_waking) p->sched_class->task_waking(p); @@ -2490,27 +2582,10 @@ try_to_wake_up(struct task_struct *p, un cpu = select_task_rq(p, SD_BALANCE_WAKE, wake_flags); #endif /* CONFIG_SMP */ - rq = cpu_rq(cpu); - raw_spin_lock(&rq->lock); - -#ifdef CONFIG_SMP - if (cpu != task_cpu(p)) - set_task_cpu(p, cpu); - - if (p->sched_contributes_to_load) - rq->nr_uninterruptible--; -#endif - - activate_task(rq, p, ENQUEUE_WAKEUP | ENQUEUE_WAKING); -out_running: - ttwu_do_wakeup(rq, p, wake_flags); - success = 1; - __task_rq_unlock(rq); - + ttwu_queue(p, cpu); ttwu_stat(p, cpu, wake_flags); out: raw_spin_unlock_irqrestore(&p->pi_lock, flags); - put_cpu(); return success; } Index: linux-2.6/kernel/sched_features.h =================================================================== --- linux-2.6.orig/kernel/sched_features.h +++ linux-2.6/kernel/sched_features.h @@ -64,3 +64,5 @@ SCHED_FEAT(OWNER_SPIN, 1) * Decrement CPU power based on irq activity */ SCHED_FEAT(NONIRQ_POWER, 1) + +SCHED_FEAT(TTWU_FORCE_REMOTE, 0) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/