Merge tag 'sched-core-2022-03-22' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull scheduler updates from Ingo Molnar:

 - Cleanups for SCHED_DEADLINE

 - Tracing updates/fixes

 - CPU Accounting fixes

 - First wave of changes to optimize the overhead of the scheduler
   build, from the fast-headers tree - including placeholder *_api.h
   headers for later header split-ups.

 - Preempt-dynamic using static_branch() for ARM64

 - Isolation housekeeping mask rework; preperatory for further changes

 - NUMA-balancing: deal with CPU-less nodes

 - NUMA-balancing: tune systems that have multiple LLC cache domains per
   node (eg. AMD)

 - Updates to RSEQ UAPI in preparation for glibc usage

 - Lots of RSEQ/selftests, for same

 - Add Suren as PSI co-maintainer

* tag 'sched-core-2022-03-22' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (81 commits)
  sched/headers: ARM needs asm/paravirt_api_clock.h too
  sched/numa: Fix boot crash on arm64 systems
  headers/prep: Fix header to build standalone: <linux/psi.h>
  sched/headers: Only include <linux/entry-common.h> when CONFIG_GENERIC_ENTRY=y
  cgroup: Fix suspicious rcu_dereference_check() usage warning
  sched/preempt: Tell about PREEMPT_DYNAMIC on kernel headers
  sched/topology: Remove redundant variable and fix incorrect type in build_sched_domains
  sched/deadline,rt: Remove unused parameter from pick_next_[rt|dl]_entity()
  sched/deadline,rt: Remove unused functions for !CONFIG_SMP
  sched/deadline: Use __node_2_[pdl|dle]() and rb_first_cached() consistently
  sched/deadline: Merge dl_task_can_attach() and dl_cpu_busy()
  sched/deadline: Move bandwidth mgmt and reclaim functions into sched class source file
  sched/deadline: Remove unused def_dl_bandwidth
  sched/tracing: Report TASK_RTLOCK_WAIT tasks as TASK_UNINTERRUPTIBLE
  sched/tracing: Don't re-read p->state when emitting sched_switch event
  sched/rt: Plug rt_mutex_setprio() vs push_rt_task() race
  sched/cpuacct: Remove redundant RCU read lock
  sched/cpuacct: Optimize away RCU read lock
  sched/cpuacct: Fix charge percpu cpuusage
  sched/headers: Reorganize, clean up and optimize kernel/sched/sched.h dependencies
  ...

2 files changed, 55 insertions, 0 deletions

diff --git a/Documentation/scheduler/index.rst b/Documentation/scheduler/index.rst
index 693eaac769a7..b430d856056a 100644
--- a/Documentation/scheduler/index.rst
+++ b/Documentation/scheduler/index.rst
@@ -18,6 +18,7 @@ Linux Scheduler
     sched-nice-design
     sched-rt-group
     sched-stats
+    sched-debug
 
     text_files
 
diff --git a/Documentation/scheduler/sched-debug.rst b/Documentation/scheduler/sched-debug.rst
new file mode 100644
index 000000000000..4d3d24f2a439
--- /dev/null
+++ b/Documentation/scheduler/sched-debug.rst
@@ -0,0 +1,54 @@
+=================
+Scheduler debugfs
+=================
+
+Booting a kernel with CONFIG_SCHED_DEBUG=y will give access to
+scheduler specific debug files under /sys/kernel/debug/sched. Some of
+those files are described below.
+
+numa_balancing
+==============
+
+`numa_balancing` directory is used to hold files to control NUMA
+balancing feature.  If the system overhead from the feature is too
+high then the rate the kernel samples for NUMA hinting faults may be
+controlled by the `scan_period_min_ms, scan_delay_ms,
+scan_period_max_ms, scan_size_mb` files.
+
+
+scan_period_min_ms, scan_delay_ms, scan_period_max_ms, scan_size_mb
+-------------------------------------------------------------------
+
+Automatic NUMA balancing scans tasks address space and unmaps pages to
+detect if pages are properly placed or if the data should be migrated to a
+memory node local to where the task is running.  Every "scan delay" the task
+scans the next "scan size" number of pages in its address space. When the
+end of the address space is reached the scanner restarts from the beginning.
+
+In combination, the "scan delay" and "scan size" determine the scan rate.
+When "scan delay" decreases, the scan rate increases.  The scan delay and
+hence the scan rate of every task is adaptive and depends on historical
+behaviour. If pages are properly placed then the scan delay increases,
+otherwise the scan delay decreases.  The "scan size" is not adaptive but
+the higher the "scan size", the higher the scan rate.
+
+Higher scan rates incur higher system overhead as page faults must be
+trapped and potentially data must be migrated. However, the higher the scan
+rate, the more quickly a tasks memory is migrated to a local node if the
+workload pattern changes and minimises performance impact due to remote
+memory accesses. These files control the thresholds for scan delays and
+the number of pages scanned.
+
+``scan_period_min_ms`` is the minimum time in milliseconds to scan a
+tasks virtual memory. It effectively controls the maximum scanning
+rate for each task.
+
+``scan_delay_ms`` is the starting "scan delay" used for a task when it
+initially forks.
+
+``scan_period_max_ms`` is the maximum time in milliseconds to scan a
+tasks virtual memory. It effectively controls the minimum scanning
+rate for each task.
+
+``scan_size_mb`` is how many megabytes worth of pages are scanned for
+a given scan.