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sched: Make struct sched_statistics independent of fair sched class

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If we want to use the schedstats facility to trace other sched classes, we
should make it independent of fair sched class. The struct sched_statistics
is the schedular statistics of a task_struct or a task_group. So we can
move it into struct task_struct and struct task_group to achieve the goal.

After the patch, schestats are orgnized as follows,

    struct task_struct {
       ...
       struct sched_entity se;
       struct sched_rt_entity rt;
       struct sched_dl_entity dl;
       ...
       struct sched_statistics stats;
       ...
   };

Regarding the task group, schedstats is only supported for fair group
sched, and a new struct sched_entity_stats is introduced, suggested by
Peter -

    struct sched_entity_stats {
        struct sched_entity     se;
        struct sched_statistics stats;
    } __no_randomize_layout;

Then with the se in a task_group, we can easily get the stats.

The sched_statistics members may be frequently modified when schedstats is
enabled, in order to avoid impacting on random data which may in the same
cacheline with them, the struct sched_statistics is defined as cacheline
aligned.

As this patch changes the core struct of scheduler, so I verified the
performance it may impact on the scheduler with 'perf bench sched
pipe', suggested by Mel. Below is the result, in which all the values
are in usecs/op.
                                  Before               After
      kernel.sched_schedstats=0  5.2~5.4               5.2~5.4
      kernel.sched_schedstats=1  5.3~5.5               5.3~5.5
[These data is a little difference with the earlier version, that is
 because my old test machine is destroyed so I have to use a new
 different test machine.]

Almost no impact on the sched performance.

No functional change.

[lkp@intel.com: reported build failure in earlier version]

Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Mel Gorman <mgorman@suse.de>
Link: https://lore.kernel.org/r/20210905143547.4668-3-laoar.shao@gmail.com
This commit is contained in:
Yafang Shao 2021-09-05 14:35:41 +00:00 • committed by Peter Zijlstra
parent a2dcb276ff
commit ceeadb83ae
8 changed files with 143 additions and 100 deletions
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6
include/linux/sched.h
View file

@ -522,7 +522,7 @@ struct sched_statistics {
u64 nr_wakeups_passive;
u64 nr_wakeups_idle;
#endif
};
} ____cacheline_aligned;
struct sched_entity {
/* For load-balancing: */
@ -538,8 +538,6 @@ struct sched_entity {
u64 nr_migrations;
struct sched_statistics statistics;
#ifdef CONFIG_FAIR_GROUP_SCHED
int depth;
struct sched_entity *parent;
@ -803,6 +801,8 @@ struct task_struct {
struct uclamp_se uclamp[UCLAMP_CNT];
#endif
struct sched_statistics stats;
#ifdef CONFIG_PREEMPT_NOTIFIERS
/* List of struct preempt_notifier: */
struct hlist_head preempt_notifiers;