From df65cdbf6bc82e79658c35e14221fef34f4db6d0 Mon Sep 17 00:00:00 2001 From: Andrew Morton Date: Sun, 9 May 2004 23:28:57 -0700 Subject: [PATCH] [PATCH] sched: passive balancing damping From: Nick Piggin This patch starts to balance woken processes when half the relevant domain's imbalance_pct is reached. Previously balancing would start after a small, constant difference in waker/wakee runqueue loads was reached, which would cause too much process movement when there are lots of processes running. It also turns wake balancing into a domain flag while previously it was always on. Now sched domains can "soft partition" an SMP system without using processor affinities. --- include/linux/sched.h | 9 ++++++--- kernel/sched.c | 35 +++++++++++++++++++---------------- 2 files changed, 25 insertions(+), 19 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index e47ff84b47615..1ff71bf1f5ea3 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -549,7 +549,8 @@ do { if (atomic_dec_and_test(&(tsk)->usage)) __put_task_struct(tsk); } while(0) #define SD_BALANCE_EXEC 2 /* Balance on exec */ #define SD_WAKE_IDLE 4 /* Wake to idle CPU on task wakeup */ #define SD_WAKE_AFFINE 8 /* Wake task to waking CPU */ -#define SD_SHARE_CPUPOWER 16 /* Domain members share cpu power */ +#define SD_WAKE_BALANCE 16 /* Perform balancing at task wakeup */ +#define SD_SHARE_CPUPOWER 32 /* Domain members share cpu power */ struct sched_group { struct sched_group *next; /* Must be a circular list */ @@ -618,7 +619,8 @@ struct sched_domain { .cache_nice_tries = 1, \ .per_cpu_gain = 100, \ .flags = SD_BALANCE_NEWIDLE \ - | SD_WAKE_AFFINE, \ + | SD_WAKE_AFFINE \ + | SD_WAKE_BALANCE, \ .last_balance = jiffies, \ .balance_interval = 1, \ .nr_balance_failed = 0, \ @@ -637,7 +639,8 @@ struct sched_domain { .cache_hot_time = (10*1000000), \ .cache_nice_tries = 1, \ .per_cpu_gain = 100, \ - .flags = SD_BALANCE_EXEC, \ + .flags = SD_BALANCE_EXEC \ + | SD_WAKE_BALANCE, \ .last_balance = jiffies, \ .balance_interval = 1, \ .nr_balance_failed = 0, \ diff --git a/kernel/sched.c b/kernel/sched.c index 32c0dc14ceb45..c6d7192eae5af 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -761,25 +761,28 @@ static int try_to_wake_up(task_t * p, unsigned int state, int sync) new_cpu = this_cpu; /* Wake to this CPU if we can */ /* - * Passive load balancing. If the queues are very out of balance - * we might as well balance here rather than the periodic load - * balancing. - */ - if (load > this_load + SCHED_LOAD_SCALE*2) - goto out_set_cpu; - - /* - * Migrate the task to the waking domain. - * Do not violate hard affinity. + * Scan domains for affine wakeup and passive balancing + * possibilities. */ for_each_domain(this_cpu, sd) { - if (!(sd->flags & SD_WAKE_AFFINE)) - break; - if (task_hot(p, rq->timestamp_last_tick, sd)) - break; + unsigned int imbalance; + /* + * Start passive balancing when half the imbalance_pct + * limit is reached. + */ + imbalance = sd->imbalance_pct + (sd->imbalance_pct - 100) / 2; - if (cpu_isset(cpu, sd->span)) - goto out_set_cpu; + if ( ((sd->flags & SD_WAKE_AFFINE) && + !task_hot(p, rq->timestamp_last_tick, sd)) + || ((sd->flags & SD_WAKE_BALANCE) && + imbalance*this_load <= 100*load) ) { + /* + * Now sd has SD_WAKE_AFFINE and p is cache cold in sd + * or sd has SD_WAKE_BALANCE and there is an imbalance + */ + if (cpu_isset(cpu, sd->span)) + goto out_set_cpu; + } } new_cpu = cpu; /* Could not wake to this_cpu. Wake to cpu instead */ -- 2.53.0