[GIT PULL] scheduler fixes

Ingo Molnar
2017-12-06T22:22:09Z

Linus,

Please pull the latest sched-urgent-for-linus git tree from:

git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git sched-urgent-for-linus

# HEAD: a4c3c04974d648ee6e1a09ef4131eb32a02ab494 sched/fair: Update and fix the runnable propagation rule

This includes a fix for the add_wait_queue() queue ordering brown paperbag bug,
plus PELT accounting fixes for cgroups scheduling artifacts.

Thanks,

Ingo

------------------>
Omar Sandoval (1):
sched/wait: Fix add_wait_queue() behavioral change

Vincent Guittot (1):
sched/fair: Update and fix the runnable propagation rule

kernel/sched/fair.c | 102 +++++++++++++++++++++++++++++++++++++---------------
kernel/sched/wait.c | 2 +-
2 files changed, 74 insertions(+), 30 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 4037e19bbca2..2fe3aa853e4d 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3413,9 +3413,9 @@ void set_task_rq_fair(struct sched_entity *se,
* _IFF_ we look at the pure running and runnable sums. Because they
* represent the very same entity, just at different points in the hierarchy.
*
- *
- * Per the above update_tg_cfs_util() is trivial (and still 'wrong') and
- * simply copies the running sum over.
+ * Per the above update_tg_cfs_util() is trivial and simply copies the running
+ * sum over (but still wrong, because the group entity and group rq do not have
+ * their PELT windows aligned).
*
* However, update_tg_cfs_runnable() is more complex. So we have:
*
@@ -3424,11 +3424,11 @@ void set_task_rq_fair(struct sched_entity *se,
* And since, like util, the runnable part should be directly transferable,
* the following would _appear_ to be the straight forward approach:
*
- * grq->avg.load_avg = grq->load.weight * grq->avg.running_avg (3)
+ * grq->avg.load_avg = grq->load.weight * grq->avg.runnable_avg (3)
*
* And per (1) we have:
*
- * ge->avg.running_avg == grq->avg.running_avg
+ * ge->avg.runnable_avg == grq->avg.runnable_avg
*
* Which gives:
*
@@ -3447,27 +3447,28 @@ void set_task_rq_fair(struct sched_entity *se,
* to (shortly) return to us. This only works by keeping the weights as
* integral part of the sum. We therefore cannot decompose as per (3).
*
- * OK, so what then?
+ * Another reason this doesn't work is that runnable isn't a 0-sum entity.
+ * Imagine a rq with 2 tasks that each are runnable 2/3 of the time. Then the
+ * rq itself is runnable anywhere between 2/3 and 1 depending on how the
+ * runnable section of these tasks overlap (or not). If they were to perfectly
+ * align the rq as a whole would be runnable 2/3 of the time. If however we
+ * always have at least 1 runnable task, the rq as a whole is always runnable.
*
+ * So we'll have to approximate.. :/
*
- * Another way to look at things is:
+ * Given the constraint:
*
- * grq->avg.load_avg = \Sum se->avg.load_avg
+ * ge->avg.running_sum <= ge->avg.runnable_sum <= LOAD_AVG_MAX
*
- * Therefore, per (2):
+ * We can construct a rule that adds runnable to a rq by assuming minimal
+ * overlap.
*
- * grq->avg.load_avg = \Sum se->load.weight * se->avg.runnable_avg
+ * On removal, we'll assume each task is equally runnable; which yields:
*
- * And the very thing we're propagating is a change in that sum (someone
- * joined/left). So we can easily know the runnable change, which would be, per
- * (2) the already tracked se->load_avg divided by the corresponding
- * se->weight.
+ * grq->avg.runnable_sum = grq->avg.load_sum / grq->load.weight
*
- * Basically (4) but in differential form:
+ * XXX: only do this for the part of runnable > running ?
*
- * d(runnable_avg) += se->avg.load_avg / se->load.weight
- * (5)
- * ge->avg.load_avg += ge->load.weight * d(runnable_avg)
*/

static inline void
@@ -3479,6 +3480,14 @@ update_tg_cfs_util(struct cfs_rq *cfs_rq, struct sched_entity *se, struct cfs_rq
if (!delta)
return;

+ /*
+ * The relation between sum and avg is:
+ *
+ * LOAD_AVG_MAX - 1024 + sa->period_contrib
+ *
+ * however, the PELT windows are not aligned between grq and gse.
+ */
+
/* Set new sched_entity's utilization */
se->avg.util_avg = gcfs_rq->avg.util_avg;
se->avg.util_sum = se->avg.util_avg * LOAD_AVG_MAX;
@@ -3491,33 +3500,68 @@ update_tg_cfs_util(struct cfs_rq *cfs_rq, struct sched_entity *se, struct cfs_rq
static inline void
update_tg_cfs_runnable(struct cfs_rq *cfs_rq, struct sched_entity *se, struct cfs_rq *gcfs_rq)
{
- long runnable_sum = gcfs_rq->prop_runnable_sum;
- long runnable_load_avg, load_avg;
- s64 runnable_load_sum, load_sum;
+ long delta_avg, running_sum, runnable_sum = gcfs_rq->prop_runnable_sum;
+ unsigned long runnable_load_avg, load_avg;
+ u64 runnable_load_sum, load_sum = 0;
+ s64 delta_sum;

if (!runnable_sum)
return;

gcfs_rq->prop_runnable_sum = 0;

+ if (runnable_sum >= 0) {
+ /*
+ * Add runnable; clip at LOAD_AVG_MAX. Reflects that until
+ * the CPU is saturated running == runnable.
+ */
+ runnable_sum += se->avg.load_sum;
+ runnable_sum = min(runnable_sum, (long)LOAD_AVG_MAX);
+ } else {
+ /*
+ * Estimate the new unweighted runnable_sum of the gcfs_rq by
+ * assuming all tasks are equally runnable.
+ */
+ if (scale_load_down(gcfs_rq->load.weight)) {
+ load_sum = div_s64(gcfs_rq->avg.load_sum,
+ scale_load_down(gcfs_rq->load.weight));
+ }
+
+ /* But make sure to not inflate se's runnable */
+ runnable_sum = min(se->avg.load_sum, load_sum);
+ }
+
+ /*
+ * runnable_sum can't be lower than running_sum
+ * As running sum is scale with cpu capacity wehreas the runnable sum
+ * is not we rescale running_sum 1st
+ */
+ running_sum = se->avg.util_sum /
+ arch_scale_cpu_capacity(NULL, cpu_of(rq_of(cfs_rq)));
+ runnable_sum = max(runnable_sum, running_sum);
+
load_sum = (s64)se_weight(se) * runnable_sum;
load_avg = div_s64(load_sum, LOAD_AVG_MAX);

- add_positive(&se->avg.load_sum, runnable_sum);
- add_positive(&se->avg.load_avg, load_avg);
+ delta_sum = load_sum - (s64)se_weight(se) * se->avg.load_sum;
+ delta_avg = load_avg - se->avg.load_avg;

- add_positive(&cfs_rq->avg.load_avg, load_avg);
- add_positive(&cfs_rq->avg.load_sum, load_sum);
+ se->avg.load_sum = runnable_sum;
+ se->avg.load_avg = load_avg;
+ add_positive(&cfs_rq->avg.load_avg, delta_avg);
+ add_positive(&cfs_rq->avg.load_sum, delta_sum);

runnable_load_sum = (s64)se_runnable(se) * runnable_sum;
runnable_load_avg = div_s64(runnable_load_sum, LOAD_AVG_MAX);
+ delta_sum = runnable_load_sum - se_weight(se) * se->avg.runnable_load_sum;
+ delta_avg = runnable_load_avg - se->avg.runnable_load_avg;

- add_positive(&se->avg.runnable_load_sum, runnable_sum);
- add_positive(&se->avg.runnable_load_avg, runnable_load_avg);
+ se->avg.runnable_load_sum = runnable_sum;
+ se->avg.runnable_load_avg = runnable_load_avg;

if (se->on_rq) {
- add_positive(&cfs_rq->avg.runnable_load_avg, runnable_load_avg);
- add_positive(&cfs_rq->avg.runnable_load_sum, runnable_load_sum);
+ add_positive(&cfs_rq->avg.runnable_load_avg, delta_avg);
+ add_positive(&cfs_rq->avg.runnable_load_sum, delta_sum);
}
}

diff --git a/kernel/sched/wait.c b/kernel/sched/wait.c
index 98feab7933c7..929ecb7d6b78 100644
--- a/kernel/sched/wait.c
+++ b/kernel/sched/wait.c
@@ -27,7 +27,7 @@ void add_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq

wq_entry->flags &= ~WQ_FLAG_EXCLUSIVE;
spin_lock_irqsave(&wq_head->lock, flags);
- __add_wait_queue_entry_tail(wq_head, wq_entry);
+ __add_wait_queue(wq_head, wq_entry);
spin_unlock_irqrestore(&wq_head->lock, flags);
}
EXPORT_SYMBOL(add_wait_queue);