Commit df65cdbf authored by Andrew Morton's avatar Andrew Morton Committed by Linus Torvalds

[PATCH] sched: passive balancing damping

From: Nick Piggin <nickpiggin@yahoo.com.au>

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.
parent 237eaf03
......@@ -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, \
......
......@@ -761,26 +761,29 @@ 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.
* Scan domains for affine wakeup and passive balancing
* possibilities.
*/
if (load > this_load + SCHED_LOAD_SCALE*2)
goto out_set_cpu;
for_each_domain(this_cpu, sd) {
unsigned int imbalance;
/*
* Migrate the task to the waking domain.
* Do not violate hard affinity.
* Start passive balancing when half the imbalance_pct
* limit is reached.
*/
for_each_domain(this_cpu, sd) {
if (!(sd->flags & SD_WAKE_AFFINE))
break;
if (task_hot(p, rq->timestamp_last_tick, sd))
break;
imbalance = sd->imbalance_pct + (sd->imbalance_pct - 100) / 2;
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 */
out_set_cpu:
......
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