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Date: Sat, 28 Nov 2020 11:08:43 +0800
From: Yafang Shao <laoar.shao@...il.com>
To: Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Juri Lelli <juri.lelli@...hat.com>,
Vincent Guittot <vincent.guittot@...aro.org>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Steven Rostedt <rostedt@...dmis.org>,
Benjamin Segall <bsegall@...gle.com>,
Mel Gorman <mgorman@...e.de>, bristot@...hat.com,
jun qian <qianjun.kernel@...il.com>
Cc: LKML <linux-kernel@...r.kernel.org>, linux-rt-users@...r.kernel.org
Subject: Re: [RFC PATCH v3 0/5] sched: support schedstats for RT sched class
On Sat, Nov 28, 2020 at 12:12 AM Yafang Shao <laoar.shao@...il.com> 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. This patch enable it for RT sched class
> as well.
>
> - Structure
>
> Before we make schedstats available for RT sched class, we should make
> struct sched_statistics independent of fair sched class first.
>
>
> 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.
>
> Below is the detailed explaination of the change in the structs.
>
> The struct before this patch:
>
> struct task_struct { |-> struct sched_entity {
> ... | ...
> struct sched_entity *se; ---| struct sched_statistics statistics;
> struct sched_rt_entity *rt; ...
> ... ...
> }; };
>
> struct task_group { |--> se[0]->statistics : schedstats of CPU0
> ... |
> #ifdef CONFIG_FAIR_GROUP_SCHED |
> struct sched_entity **se; --|--> se[1]->statistics : schedstats of CPU1
> |
> #endif |
> |--> se[N]->statistics : schedstats of CPUn
>
> #ifdef CONFIG_FAIR_GROUP_SCHED
> struct sched_rt_entity **rt_se; (N/A)
> #endif
> ...
> };
>
> The '**se' in task_group is allocated in the fair sched class, which is
> hard to be reused by other sched class.
>
> The struct after this patch:
> 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
> ...
> };
>
> After the patch it is clearly that both of se or rt_se can easily get the
> sched_statistics by a task_struct or a task_group.
>
> - Function Interface
>
> The original prototype of the schedstats helpers are
>
> update_stats_wait_*(struct cfs_rq *cfs_rq, struct sched_entity *se)
>
> The cfs_rq in these helpers is used to get the rq_clock, and the se is
> used to get the struct sched_statistics and the struct task_struct. In
> order to make these helpers available by all sched classes, we can pass
> the rq, sched_statistics and task_struct directly.
>
> Then the new helpers are
>
> update_stats_wait_*(struct rq *rq, struct task_struct *p,
> struct sched_statistics *stats)
>
> which are independent of fair sched class.
>
> To avoid vmlinux growing too large or introducing ovehead when
> !schedstat_enabled(), some new helpers after schedstat_enabled() are also
> introduced, Suggested by Mel. These helpers are in sched/stats.c,
>
> __update_stats_wait_*(struct rq *rq, struct task_struct *p,
> struct sched_statistics *stats)
>
> - Implementation
>
> After we make the struct sched_statistics and the helpers of it
> independent of fair sched class, we can easily use the schedstats
> facility for RT sched class.
>
> The schedstat usage in RT sched class is similar with fair sched class,
> for example,
> fair RT
> enqueue update_stats_enqueue_fair update_stats_enqueue_rt
> dequeue update_stats_dequeue_fair update_stats_dequeue_rt
> put_prev_task update_stats_wait_start update_stats_wait_start
> set_next_task update_stats_wait_end update_stats_wait_end
>
> - Usage
>
> The user can get the schedstats information in the same way in fair sched
> class. For example,
> fair RT
> task show /proc/[pid]/sched /proc/[pid]/sched
> group show cpu.stat in cgroup cpu.stat in cgroup
>
> The sched:sched_stat_{wait, sleep, iowait, blocked} tracepoints can
> be used to trace RT tasks as well. sched_stat_runtime can also be
> supported in the future if it is helpful.
>
> Yafang Shao (5):
> sched: don't include stats.h in sched.h
> 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, rt: support schedstats for RT sched class
>
> include/linux/sched.h | 3 +-
> kernel/sched/core.c | 25 +++--
> kernel/sched/deadline.c | 5 +-
> kernel/sched/debug.c | 82 +++++++--------
> kernel/sched/fair.c | 209 +++++++++++++++------------------------
> kernel/sched/idle.c | 1 +
> kernel/sched/rt.c | 178 ++++++++++++++++++++++++++++++++-
> kernel/sched/sched.h | 13 ++-
> kernel/sched/stats.c | 105 ++++++++++++++++++++
> kernel/sched/stats.h | 80 +++++++++++++++
> kernel/sched/stop_task.c | 5 +-
> 11 files changed, 517 insertions(+), 189 deletions(-)
>
> --
> 2.18.4
>
Ah, the patch #5 is missed,pls ignore this patchset. I will resend them.
--
Thanks
Yafang
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