linux.git/kernel/sched/stop_task.c, branch v6.18.21

sched/smp: Use the SMP version of the stop-CPU scheduling class

2025-06-13T06:47:21+00:00

Simplify the scheduler by making CONFIG_SMP=y code in the stop-CPU
scheduling class unconditional.

Signed-off-by: Ingo Molnar 
Acked-by: Peter Zijlstra 
Cc: Dietmar Eggemann 
Cc: Juri Lelli 
Cc: Linus Torvalds 
Cc: Mel Gorman 
Cc: Sebastian Andrzej Siewior 
Cc: Shrikanth Hegde 
Cc: Steven Rostedt 
Cc: Valentin Schneider 
Cc: Vincent Guittot 
Link: https://lore.kernel.org/r/20250528080924.2273858-36-mingo@kernel.org

sched: Make clangd usable

2025-06-11T09:20:53+00:00

Due to the weird Makefile setup of sched the various files do not
compile as stand alone units. The new generation of editors are trying
to do just this -- mostly to offer fancy things like completions but
also better syntax highlighting and code navigation.

Specifically, I've been playing around with neovim and clangd.

Setting up clangd on the kernel source is a giant pain in the arse
(this really should be improved), but once you do manage, you run into
dumb stuff like the above.

Fix up the scheduler files to at least pretend to work.

Signed-off-by: Peter Zijlstra (Intel) 
Acked-by: Ingo Molnar 
Tested-by: Juri Lelli 
Link: https://lkml.kernel.org/r/20250523164348.GN39944@noisy.programming.kicks-ass.net

sched: Add put_prev_task(.next)

2024-09-03T13:26:32+00:00

In order to tell the previous sched_class what the next task is, add
put_prev_task(.next).

Notable SCX will use this to:

 1) determine the next task will leave the SCX sched class and push
    the current task to another CPU if possible.
 2) statistics on how often and which other classes preempt it

Signed-off-by: Peter Zijlstra (Intel) 
Link: https://lore.kernel.org/r/20240813224016.367421076@infradead.org

sched: Rework pick_next_task()

2024-09-03T13:26:31+00:00

The current rule is that:

  pick_next_task() := pick_task() + set_next_task(.first = true)

And many classes implement it directly as such. Change things around
to make pick_next_task() optional while also changing the definition to:

  pick_next_task(prev) := pick_task() + put_prev_task() + set_next_task(.first = true)

The reason is that sched_ext would like to have a 'final' call that
knows the next task. By placing put_prev_task() right next to
set_next_task() (as it already is for sched_core) this becomes
trivial.

As a bonus, this is a nice cleanup on its own.

Signed-off-by: Peter Zijlstra (Intel) 
Link: https://lore.kernel.org/r/20240813224016.051225657@infradead.org

sched: Allow sched_class::dequeue_task() to fail

2024-08-17T09:06:41+00:00

Change the function signature of sched_class::dequeue_task() to return
a boolean, allowing future patches to 'fail' dequeue.

Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Valentin Schneider 
Tested-by: Valentin Schneider 
Link: https://lkml.kernel.org/r/20240727105028.864630153@infradead.org

sched: Unify runtime accounting across classes

2023-11-15T08:57:48+00:00

All classes use sched_entity::exec_start to track runtime and have
copies of the exact same code around to compute runtime.

Collapse all that.

Signed-off-by: Peter Zijlstra (Intel) 
Signed-off-by: Daniel Bristot de Oliveira 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Phil Auld 
Reviewed-by: Valentin Schneider 
Reviewed-by: Steven Rostedt (Google) 
Link: https://lkml.kernel.org/r/54d148a144f26d9559698c4dd82d8859038a7380.1699095159.git.bristot@kernel.org

sched/fair: Rename check_preempt_curr() to wakeup_preempt()

2023-09-19T08:40:10+00:00

The name is a bit opaque - make it clear that this is about wakeup
preemption.

Also rename the ->check_preempt_curr() methods similarly.

Signed-off-by: Ingo Molnar 
Acked-by: Peter Zijlstra (Intel)

sched: Add update_current_exec_runtime helper

2022-08-26T22:05:35+00:00

Wrap repeated code in helper function update_current_exec_runtime for
update the exec time of the current.

Signed-off-by: Shang XiaoJing 
Signed-off-by: Peter Zijlstra (Intel) 
Link: https://lkml.kernel.org/r/20220824082856.15674-1-shangxiaojing@huawei.com

sched/headers: Introduce kernel/sched/build_utility.c and build multiple .c files there

2022-02-23T09:58:33+00:00

Collect all utility functionality source code files into a single kernel/sched/build_utility.c file,
via #include-ing the .c files:

    kernel/sched/clock.c
    kernel/sched/completion.c
    kernel/sched/loadavg.c
    kernel/sched/swait.c
    kernel/sched/wait_bit.c
    kernel/sched/wait.c

CONFIG_CPU_FREQ:
    kernel/sched/cpufreq.c

CONFIG_CPU_FREQ_GOV_SCHEDUTIL:
    kernel/sched/cpufreq_schedutil.c

CONFIG_CGROUP_CPUACCT:
    kernel/sched/cpuacct.c

CONFIG_SCHED_DEBUG:
    kernel/sched/debug.c

CONFIG_SCHEDSTATS:
    kernel/sched/stats.c

CONFIG_SMP:
   kernel/sched/cpupri.c
   kernel/sched/stop_task.c
   kernel/sched/topology.c

CONFIG_SCHED_CORE:
   kernel/sched/core_sched.c

CONFIG_PSI:
   kernel/sched/psi.c

CONFIG_MEMBARRIER:
   kernel/sched/membarrier.c

CONFIG_CPU_ISOLATION:
   kernel/sched/isolation.c

CONFIG_SCHED_AUTOGROUP:
   kernel/sched/autogroup.c

The goal is to amortize the 60+ KLOC header bloat from over a dozen build units into
a single build unit.

The build time of build_utility.c also roughly matches the build time of core.c and
fair.c - allowing better load-balancing of scheduler-only rebuilds.

Signed-off-by: Ingo Molnar 
Reviewed-by: Peter Zijlstra

sched: Make struct sched_statistics independent of fair sched class

2021-10-05T13:51:45+00:00

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 
Signed-off-by: Peter Zijlstra (Intel) 
Acked-by: Mel Gorman 
Link: https://lore.kernel.org/r/20210905143547.4668-3-laoar.shao@gmail.com