leandrof/linux
1
0
Fork 0
forked from Minki/linux
Code Issues Pull Requests Packages Projects Releases Wiki Activity

sched/fair: Avoid stale CPU util_est value for schedutil in task dequeue

Browse Source 
CPU (root cfs_rq) estimated utilization (util_est) is currently used in
dequeue_task_fair() to drive frequency selection before it is updated.

with:

CPU_util        : rq->cfs.avg.util_avg
CPU_util_est    : rq->cfs.avg.util_est
CPU_utilization : max(CPU_util, CPU_util_est)
task_util       : p->se.avg.util_avg
task_util_est   : p->se.avg.util_est

dequeue_task_fair():

    /* (1) CPU_util and task_util update + inform schedutil about
           CPU_utilization changes */
    for_each_sched_entity() /* 2 loops */
        (dequeue_entity() ->) update_load_avg() -> cfs_rq_util_change()
         -> cpufreq_update_util() ->...-> sugov_update_[shared\|single]
         -> sugov_get_util() -> cpu_util_cfs()

    /* (2) CPU_util_est and task_util_est update */
    util_est_dequeue()

cpu_util_cfs() uses CPU_utilization which could lead to a false (too
high) utilization value for schedutil in task ramp-down or ramp-up
scenarios during task dequeue.

To mitigate the issue split the util_est update (2) into:

 (A) CPU_util_est update in util_est_dequeue()
 (B) task_util_est update in util_est_update()

Place (A) before (1) and keep (B) where (2) is. The latter is necessary
since (B) relies on task_util update in (1).

Fixes: 7f65ea42eb ("sched/fair: Add util_est on top of PELT")
Signed-off-by: Xuewen Yan <xuewen.yan@unisoc.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lkml.kernel.org/r/1608283672-18240-1-git-send-email-xuewen.yan94@gmail.com
This commit is contained in:
Xuewen Yan 2020-12-18 17:27:52 +08:00 committed by Peter Zijlstra
parent 0301925dd0
commit 8c1f560c1e
1 changed files with 28 additions and 15 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

43
kernel/sched/fair.c
View File

@ -3943,6 +3943,22 @@ static inline void util_est_enqueue(struct cfs_rq *cfs_rq,
trace_sched_util_est_cfs_tp(cfs_rq);
}
static inline void util_est_dequeue(struct cfs_rq *cfs_rq,
struct task_struct *p)
{
unsigned int enqueued;
if (!sched_feat(UTIL_EST))
return;
/* Update root cfs_rq's estimated utilization */
enqueued = cfs_rq->avg.util_est.enqueued;
enqueued -= min_t(unsigned int, enqueued, _task_util_est(p));
WRITE_ONCE(cfs_rq->avg.util_est.enqueued, enqueued);
trace_sched_util_est_cfs_tp(cfs_rq);
}
/*
* Check if a (signed) value is within a specified (unsigned) margin,
* based on the observation that:
@ -3956,23 +3972,16 @@ static inline bool within_margin(int value, int margin)
return ((unsigned int)(value + margin - 1) < (2 * margin - 1));
}
static void
util_est_dequeue(struct cfs_rq *cfs_rq, struct task_struct *p, bool task_sleep)
static inline void util_est_update(struct cfs_rq *cfs_rq,
struct task_struct *p,
bool task_sleep)
{
long last_ewma_diff;
struct util_est ue;
int cpu;
if (!sched_feat(UTIL_EST))
return;
/* Update root cfs_rq's estimated utilization */
ue.enqueued = cfs_rq->avg.util_est.enqueued;
ue.enqueued -= min_t(unsigned int, ue.enqueued, _task_util_est(p));
WRITE_ONCE(cfs_rq->avg.util_est.enqueued, ue.enqueued);
trace_sched_util_est_cfs_tp(cfs_rq);
/*
* Skip update of task's estimated utilization when the task has not
* yet completed an activation, e.g. being migrated.
@ -4012,8 +4021,7 @@ util_est_dequeue(struct cfs_rq *cfs_rq, struct task_struct *p, bool task_sleep)
* To avoid overestimation of actual task utilization, skip updates if
* we cannot grant there is idle time in this CPU.
*/
cpu = cpu_of(rq_of(cfs_rq));
if (task_util(p) > capacity_orig_of(cpu))
if (task_util(p) > capacity_orig_of(cpu_of(rq_of(cfs_rq))))
return;
/*
@ -4096,8 +4104,11 @@ static inline void
util_est_enqueue(struct cfs_rq *cfs_rq, struct task_struct *p) {}
static inline void
util_est_dequeue(struct cfs_rq *cfs_rq, struct task_struct *p,
bool task_sleep) {}
util_est_dequeue(struct cfs_rq *cfs_rq, struct task_struct *p) {}
static inline void
util_est_update(struct cfs_rq *cfs_rq, struct task_struct *p,
bool task_sleep) {}
static inline void update_misfit_status(struct task_struct *p, struct rq *rq) {}
#endif /* CONFIG_SMP */
@ -5609,6 +5620,8 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags)
int idle_h_nr_running = task_has_idle_policy(p);
bool was_sched_idle = sched_idle_rq(rq);
util_est_dequeue(&rq->cfs, p);
for_each_sched_entity(se) {
cfs_rq = cfs_rq_of(se);
dequeue_entity(cfs_rq, se, flags);
@ -5659,7 +5672,7 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags)
rq->next_balance = jiffies;
dequeue_throttle:
util_est_dequeue(&rq->cfs, p, task_sleep);
util_est_update(&rq->cfs, p, task_sleep);
hrtick_update(rq);
}