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authorDietmar Eggemann <dietmar.eggemann@arm.com>2014-11-14 15:09:45 +0000
committerRobin Randhawa <robin.randhawa@arm.com>2015-04-09 12:26:12 +0100
commite925532d3eacdd0a174e44fb05de3adb25bdb2f0 (patch)
tree6debdd424172aafb09361764138e564fb9b0de40
parent41478595352b48f79d475bc13718acbee88ccb29 (diff)
downloadkernel-e925532d3eacdd0a174e44fb05de3adb25bdb2f0.tar.gz
sched: Make load tracking frequency scale-invariant
Apply frequency scale-invariance correction factor to load tracking. Each segment of the sched_avg::runnable_avg_sum geometric series is now scaled by the current frequency so the sched_avg::load_avg_contrib of each entity will be invariant with frequency scaling. As a result, cfs_rq::runnable_load_avg which is the sum of sched_avg::load_avg_contrib, becomes invariant too. So the load level that is returned by weighted_cpuload, stays relative to the max frequency of the cpu. Then, we want the keep the load tracking values in a 32bits type, which implies that the max value of sched_avg::{runnable|running}_avg_sum must be lower than 2^32/88761=48388 (88761 is the max weight of a task). As LOAD_AVG_MAX = 47742, arch_scale_freq_capacity must return a value less than (48388/47742) << SCHED_CAPACITY_SHIFT = 1037 (SCHED_SCALE_CAPACITY = 1024). So we define the range to [0..SCHED_SCALE_CAPACITY] in order to avoid overflow. Cc: Ingo Molnar <mingo@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com> Acked-by: Vincent Guittot <vincent.guittot@linaro.org>
-rw-r--r--kernel/sched/fair.c28
1 files changed, 16 insertions, 12 deletions
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index abfc368..17f571a 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2234,9 +2234,9 @@ static __always_inline int __update_entity_runnable_avg(u64 now, int cpu,
int runnable,
int running)
{
- u64 delta, periods;
- u32 runnable_contrib;
- int delta_w, decayed = 0;
+ u64 delta, scaled_delta, periods;
+ u32 runnable_contrib, scaled_runnable_contrib;
+ int delta_w, scaled_delta_w, decayed = 0;
unsigned long scale_freq = arch_scale_freq_capacity(NULL, cpu);
delta = now - sa->last_runnable_update;
@@ -2270,11 +2270,12 @@ static __always_inline int __update_entity_runnable_avg(u64 now, int cpu,
* period and accrue it.
*/
delta_w = 1024 - delta_w;
+ scaled_delta_w = (delta_w * scale_freq) >> SCHED_CAPACITY_SHIFT;
+
if (runnable)
- sa->runnable_avg_sum += delta_w;
+ sa->runnable_avg_sum += scaled_delta_w;
if (running)
- sa->running_avg_sum += delta_w * scale_freq
- >> SCHED_CAPACITY_SHIFT;
+ sa->running_avg_sum += scaled_delta_w;
sa->avg_period += delta_w;
delta -= delta_w;
@@ -2292,20 +2293,23 @@ static __always_inline int __update_entity_runnable_avg(u64 now, int cpu,
/* Efficiently calculate \sum (1..n_period) 1024*y^i */
runnable_contrib = __compute_runnable_contrib(periods);
+ scaled_runnable_contrib = (runnable_contrib * scale_freq)
+ >> SCHED_CAPACITY_SHIFT;
+
if (runnable)
- sa->runnable_avg_sum += runnable_contrib;
+ sa->runnable_avg_sum += scaled_runnable_contrib;
if (running)
- sa->running_avg_sum += runnable_contrib * scale_freq
- >> SCHED_CAPACITY_SHIFT;
+ sa->running_avg_sum += scaled_runnable_contrib;
sa->avg_period += runnable_contrib;
}
/* Remainder of delta accrued against u_0` */
+ scaled_delta = (delta * scale_freq) >> SCHED_CAPACITY_SHIFT;
+
if (runnable)
- sa->runnable_avg_sum += delta;
+ sa->runnable_avg_sum += scaled_delta;
if (running)
- sa->running_avg_sum += delta * scale_freq
- >> SCHED_CAPACITY_SHIFT;
+ sa->running_avg_sum += scaled_delta;
sa->avg_period += delta;
return decayed;