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sched/fair: Fix cpu_util runnable_avg arithmetic

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If we take runnable_avg in max(runnable_avg, util_avg) in cpu_util(), we
should then add or subtract task runnable_avg, but the arithmetic below
is still with task util_avg. This mixes runnable_avg with util_avg which
is incorrect.

Fix by always doing arithmetic with runnable_avg and only take
max(runnable_avg, util_avg) at the last step.

Fixes: 7d0583cf9e ("sched/fair, cpufreq: Introduce 'runnable boosting'")
Signed-off-by: Hongyan Xia <hongyan.xia@transsion.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://patch.msgid.link/20260605094318.37931-1-hongyan.xia@transsion.com
This commit is contained in:
Hongyan Xia
2026-06-05 09:43:39 +00:00
committed by Peter Zijlstra
parent f666241e6b
commit 29922fdfc2
1 changed files with 15 additions and 8 deletions
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23
kernel/sched/fair.c
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@@ -8968,25 +8968,32 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
static unsigned long
cpu_util(int cpu, struct task_struct *p, int dst_cpu, int boost)
{
bool add_task = p && task_cpu(p) != cpu && dst_cpu == cpu;
bool sub_task = p && task_cpu(p) == cpu && dst_cpu != cpu;
struct cfs_rq *cfs_rq = &cpu_rq(cpu)->cfs;
unsigned long util = READ_ONCE(cfs_rq->avg.util_avg);
unsigned long runnable;
if (boost) {
runnable = READ_ONCE(cfs_rq->avg.runnable_avg);
util = max(util, runnable);
}
/*
* If @dst_cpu is -1 or @p migrates from @cpu to @dst_cpu remove its
* contribution. If @p migrates from another CPU to @cpu add its
* contribution. In all the other cases @cpu is not impacted by the
* migration so its util_avg is already correct.
*/
if (p && task_cpu(p) == cpu && dst_cpu != cpu)
lsub_positive(&util, task_util(p));
else if (p && task_cpu(p) != cpu && dst_cpu == cpu)
if (add_task)
util += task_util(p);
else if (sub_task)
lsub_positive(&util, task_util(p));
if (boost) {
runnable = READ_ONCE(cfs_rq->avg.runnable_avg);
if (add_task)
runnable += READ_ONCE(p->se.avg.runnable_avg);
else if (sub_task)
lsub_positive(&runnable,
READ_ONCE(p->se.avg.runnable_avg));
util = max(util, runnable);
}
if (sched_feat(UTIL_EST)) {
unsigned long util_est;