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author | Dietmar Eggemann <dietmar.eggemann@arm.com> | 2015-08-14 17:23:13 +0100 |
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committer | Ingo Molnar <mingo@kernel.org> | 2015-09-13 09:52:57 +0200 |
commit | 231678b768da07d19ab5683a39eeb0c250631d02 (patch) | |
tree | 66ad1f5df8abd29456becf069a110e07f6473535 /kernel/sched | |
parent | 9e91d61d9b0ca8d865dbd59af8d0d5c5b68003e9 (diff) | |
download | linux-stable-231678b768da07d19ab5683a39eeb0c250631d02.tar.gz linux-stable-231678b768da07d19ab5683a39eeb0c250631d02.tar.bz2 linux-stable-231678b768da07d19ab5683a39eeb0c250631d02.zip |
sched/fair: Get rid of scaling utilization by capacity_orig
Utilization is currently scaled by capacity_orig, but since we now have
frequency and cpu invariant cfs_rq.avg.util_avg, frequency and cpu scaling
now happens as part of the utilization tracking itself.
So cfs_rq.avg.util_avg should no longer be scaled in cpu_util().
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Juri Lelli <Juri.Lelli@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steve Muckle <steve.muckle@linaro.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: daniel.lezcano@linaro.org <daniel.lezcano@linaro.org>
Cc: mturquette@baylibre.com <mturquette@baylibre.com>
Cc: pang.xunlei@zte.com.cn <pang.xunlei@zte.com.cn>
Cc: rjw@rjwysocki.net <rjw@rjwysocki.net>
Cc: sgurrappadi@nvidia.com <sgurrappadi@nvidia.com>
Cc: vincent.guittot@linaro.org <vincent.guittot@linaro.org>
Cc: yuyang.du@intel.com <yuyang.du@intel.com>
Link: http://lkml.kernel.org/r/55EDAF43.30500@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/sched')
-rw-r--r-- | kernel/sched/fair.c | 38 |
1 files changed, 22 insertions, 16 deletions
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 1b56d63c5322..047fd1c78a94 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -4862,33 +4862,39 @@ next: done: return target; } + /* * cpu_util returns the amount of capacity of a CPU that is used by CFS * tasks. The unit of the return value must be the one of capacity so we can * compare the utilization with the capacity of the CPU that is available for * CFS task (ie cpu_capacity). - * cfs.avg.util_avg is the sum of running time of runnable tasks on a - * CPU. It represents the amount of utilization of a CPU in the range - * [0..SCHED_LOAD_SCALE]. The utilization of a CPU can't be higher than the - * full capacity of the CPU because it's about the running time on this CPU. - * Nevertheless, cfs.avg.util_avg can be higher than SCHED_LOAD_SCALE - * because of unfortunate rounding in util_avg or just - * after migrating tasks until the average stabilizes with the new running - * time. So we need to check that the utilization stays into the range - * [0..cpu_capacity_orig] and cap if necessary. - * Without capping the utilization, a group could be seen as overloaded (CPU0 - * utilization at 121% + CPU1 utilization at 80%) whereas CPU1 has 20% of - * available capacity. + * + * cfs_rq.avg.util_avg is the sum of running time of runnable tasks plus the + * recent utilization of currently non-runnable tasks on a CPU. It represents + * the amount of utilization of a CPU in the range [0..capacity_orig] where + * capacity_orig is the cpu_capacity available at the highest frequency + * (arch_scale_freq_capacity()). + * The utilization of a CPU converges towards a sum equal to or less than the + * current capacity (capacity_curr <= capacity_orig) of the CPU because it is + * the running time on this CPU scaled by capacity_curr. + * + * Nevertheless, cfs_rq.avg.util_avg can be higher than capacity_curr or even + * higher than capacity_orig because of unfortunate rounding in + * cfs.avg.util_avg or just after migrating tasks and new task wakeups until + * the average stabilizes with the new running time. We need to check that the + * utilization stays within the range of [0..capacity_orig] and cap it if + * necessary. Without utilization capping, a group could be seen as overloaded + * (CPU0 utilization at 121% + CPU1 utilization at 80%) whereas CPU1 has 20% of + * available capacity. We allow utilization to overshoot capacity_curr (but not + * capacity_orig) as it useful for predicting the capacity required after task + * migrations (scheduler-driven DVFS). */ static int cpu_util(int cpu) { unsigned long util = cpu_rq(cpu)->cfs.avg.util_avg; unsigned long capacity = capacity_orig_of(cpu); - if (util >= SCHED_LOAD_SCALE) - return capacity; - - return (util * capacity) >> SCHED_LOAD_SHIFT; + return (util >= capacity) ? capacity : util; } /* |