by Yafang Shao

[permalink] [raw]

Subject: Re: [PATCH v2 0/6] sched: support schedstats for RT sched class

On Sat, Mar 27, 2021 at 6:13 PM Yafang Shao <[email protected]> wrote:
>
> We want to measure the latency of RT tasks in our production
> environment with schedstats facility, but currently schedstats is only
> supported for fair sched class. In order to support if for 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, both of which are independent of sched class. So we can move
> struct sched_statistics into struct task_struct and struct task_group to
> achieve the goal.
>
> After the patchset, schestats are orgnized as follows,
> struct task_struct {
> ...
> struct sched_statistics statistics;
> ...
> struct sched_entity *se;
> struct sched_rt_entity *rt;
> ...
> };
>
> struct task_group { |---> stats[0] : of CPU0
> ... |
> struct sched_statistics **stats; --|---> stats[1] : of CPU1
> ... |
> |---> stats[n] : of CPUn
> #ifdef CONFIG_FAIR_GROUP_SCHED
> struct sched_entity **se;
> #endif
> #ifdef CONFIG_RT_GROUP_SCHED
> struct sched_rt_entity **rt_se;
> #endif
> ...
> };
>
> 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.
>
> Then we can use schedstats to trace RT tasks as well, for example,
> Interface File
> task schedstats : /proc/[pid]/sched
> group schedstats: /proc/sched_debug
> tracepoints : sched:sched_stat_{runtime, wait, sleep, iowait, blocked}
>
> As PATCH #2 and #3 changes the core struct in the scheduler, so I did
> 'perf bench sched pipe' to measure the sched performance before and after
> the change, suggested by Mel. Below is the data, which are all in
> usecs/op.
> Before After
> kernel.sched_schedstats=0 6.0~6.1 6.0~6.1
> kernel.sched_schedstats=1 6.2~6.4 6.2~6.4
> No obvious difference after the change.
>
> Changes since v1:
> - Fix the build failure reported by kernel test robot.
> - Add the performance data with 'perf bench sched pipe', suggested by
> Mel.
> - Make the struct sched_statistics cacheline aligned.
> - Introduce task block time in schedstats
>
> Changes since RFC:
> - improvement of schedstats helpers, per Mel.
> - make struct schedstats independent of fair sched class
>
> Yafang Shao (6):
> sched, fair: use __schedstat_set() in set_next_entity()
> sched: make struct sched_statistics independent of fair sched class
> sched: make schedstats helpers independent of fair sched class
> sched: introduce task block time in schedstats
> sched, rt: support sched_stat_runtime tracepoint for RT sched class
> sched, rt: support schedstats for RT sched class
>
> include/linux/sched.h | 7 +-
> kernel/sched/core.c | 24 +++--
> kernel/sched/deadline.c | 4 +-
> kernel/sched/debug.c | 90 +++++++++--------
> kernel/sched/fair.c | 210 ++++++++++++++++-----------------------
> kernel/sched/rt.c | 143 +++++++++++++++++++++++++-
> kernel/sched/sched.h | 3 +
> kernel/sched/stats.c | 104 +++++++++++++++++++
> kernel/sched/stats.h | 89 +++++++++++++++++
> kernel/sched/stop_task.c | 4 +-
> 10 files changed, 489 insertions(+), 189 deletions(-)
>
> --
> 2.18.2
>

Peter, Ingo, Mel,

Any comments on this version ?

--
Thanks
Yafang