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sched/pelt: Add a new runnable average signal

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Now that runnable_load_avg has been removed, we can replace it by a new
signal that will highlight the runnable pressure on a cfs_rq. This signal
track the waiting time of tasks on rq and can help to better define the
state of rqs.

At now, only util_avg is used to define the state of a rq:
  A rq with more that around 80% of utilization and more than 1 tasks is
  considered as overloaded.

But the util_avg signal of a rq can become temporaly low after that a task
migrated onto another rq which can bias the classification of the rq.

When tasks compete for the same rq, their runnable average signal will be
higher than util_avg as it will include the waiting time and we can use
this signal to better classify cfs_rqs.

The new runnable_avg will track the runnable time of a task which simply
adds the waiting time to the running time. The runnable _avg of cfs_rq
will be the /Sum of se's runnable_avg and the runnable_avg of group entity
will follow the one of the rq similarly to util_avg.

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: "Dietmar Eggemann <dietmar.eggemann@arm.com>"
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Valentin Schneider <valentin.schneider@arm.com>
Cc: Phil Auld <pauld@redhat.com>
Cc: Hillf Danton <hdanton@sina.com>
Link: https://lore.kernel.org/r/20200224095223.13361-9-mgorman@techsingularity.net
This commit is contained in:
Vincent Guittot
2020-02-24 09:52:18 +00:00
committed by Ingo Molnar
parent 0dacee1bfa
commit 9f68395333
5 changed files with 142 additions and 31 deletions
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26
include/linux/sched.h
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@@ -356,28 +356,30 @@ struct util_est {
} __attribute__((__aligned__(sizeof(u64))));
/*
* The load_avg/util_avg accumulates an infinite geometric series
* The load/runnable/util_avg accumulates an infinite geometric series
* (see __update_load_avg_cfs_rq() in kernel/sched/pelt.c).
*
* [load_avg definition]
*
* load_avg = runnable% * scale_load_down(load)
*
* where runnable% is the time ratio that a sched_entity is runnable.
* For cfs_rq, it is the aggregated load_avg of all runnable and
* blocked sched_entities.
* [runnable_avg definition]
*
* runnable_avg = runnable% * SCHED_CAPACITY_SCALE
*
* [util_avg definition]
*
* util_avg = running% * SCHED_CAPACITY_SCALE
*
* where running% is the time ratio that a sched_entity is running on
* a CPU. For cfs_rq, it is the aggregated util_avg of all runnable
* and blocked sched_entities.
* where runnable% is the time ratio that a sched_entity is runnable and
* running% the time ratio that a sched_entity is running.
*
* load_avg and util_avg don't direcly factor frequency scaling and CPU
* capacity scaling. The scaling is done through the rq_clock_pelt that
* is used for computing those signals (see update_rq_clock_pelt())
* For cfs_rq, they are the aggregated values of all runnable and blocked
* sched_entities.
*
* The load/runnable/util_avg doesn't direcly factor frequency scaling and CPU
* capacity scaling. The scaling is done through the rq_clock_pelt that is used
* for computing those signals (see update_rq_clock_pelt())
*
* N.B., the above ratios (runnable% and running%) themselves are in the
* range of [0, 1]. To do fixed point arithmetics, we therefore scale them
@@ -401,9 +403,11 @@ struct util_est {
struct sched_avg {
u64 last_update_time;
u64 load_sum;
u64 runnable_sum;
u32 util_sum;
u32 period_contrib;
unsigned long load_avg;
unsigned long runnable_avg;
unsigned long util_avg;
struct util_est util_est;
} ____cacheline_aligned;
@@ -467,6 +471,8 @@ struct sched_entity {
struct cfs_rq *cfs_rq;
/* rq "owned" by this entity/group: */
struct cfs_rq *my_q;
/* cached value of my_q->h_nr_running */
unsigned long runnable_weight;
#endif
#ifdef CONFIG_SMP