Commit 9a7e0a90 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge tag 'sched-core-2021-11-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 

Pull scheduler updates from Thomas Gleixner:

 - Revert the printk format based wchan() symbol resolution as it can
   leak the raw value in case that the symbol is not resolvable.

 - Make wchan() more robust and work with all kind of unwinders by
   enforcing that the task stays blocked while unwinding is in progress.

 - Prevent sched_fork() from accessing an invalid sched_task_group

 - Improve asymmetric packing logic

 - Extend scheduler statistics to RT and DL scheduling classes and add
   statistics for bandwith burst to the SCHED_FAIR class.

 - Properly account SCHED_IDLE entities

 - Prevent a potential deadlock when initial priority is assigned to a
   newly created kthread. A recent change to plug a race between cpuset
   and __sched_setscheduler() introduced a new lock dependency which is
   now triggered. Break the lock dependency chain by moving the priority
   assignment to the thread function.

 - Fix the idle time reporting in /proc/uptime for NOHZ enabled systems.

 - Improve idle balancing in general and especially for NOHZ enabled
   systems.

 - Provide proper interfaces for live patching so it does not have to
   fiddle with scheduler internals.

 - Add cluster aware scheduling support.

 - A small set of tweaks for RT (irqwork, wait_task_inactive(), various
   scheduler options and delaying mmdrop)

 - The usual small tweaks and improvements all over the place

* tag 'sched-core-2021-11-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (69 commits)
  sched/fair: Cleanup newidle_balance
  sched/fair: Remove sysctl_sched_migration_cost condition
  sched/fair: Wait before decaying max_newidle_lb_cost
  sched/fair: Skip update_blocked_averages if we are defering load balance
  sched/fair: Account update_blocked_averages in newidle_balance cost
  x86: Fix __get_wchan() for !STACKTRACE
  sched,x86: Fix L2 cache mask
  sched/core: Remove rq_relock()
  sched: Improve wake_up_all_idle_cpus() take #2
  irq_work: Also rcuwait for !IRQ_WORK_HARD_IRQ on PREEMPT_RT
  irq_work: Handle some irq_work in a per-CPU thread on PREEMPT_RT
  irq_work: Allow irq_work_sync() to sleep if irq_work() no IRQ support.
  sched/rt: Annotate the RT balancing logic irqwork as IRQ_WORK_HARD_IRQ
  sched: Add cluster scheduler level for x86
  sched: Add cluster scheduler level in core and related Kconfig for ARM64
  topology: Represent clusters of CPUs within a die
  sched: Disable -Wunused-but-set-variable
  sched: Add wrapper for get_wchan() to keep task blocked
  x86: Fix get_wchan() to support the ORC unwinder
  proc: Use task_is_running() for wchan in /proc/$pid/stat
  ...
parents 57a315cd 8ea9183d

Documentation/ABI/stable/sysfs-devices-system-cpu

+15 −0
Original line number Diff line number Diff line
@@ -42,6 +42,12 @@ Description: the CPU core ID of cpuX. Typically it is the hardware platform's 
                architecture and platform dependent.

Values:         integer



What:           /sys/devices/system/cpu/cpuX/topology/cluster_id

Description:    the cluster ID of cpuX.  Typically it is the hardware platform's

                identifier (rather than the kernel's). The actual value is

                architecture and platform dependent.

Values:         integer



What:           /sys/devices/system/cpu/cpuX/topology/book_id

Description:    the book ID of cpuX. Typically it is the hardware platform's

                identifier (rather than the kernel's). The actual value is
@@ -85,6 +91,15 @@ Description: human-readable list of CPUs within the same die. 
                The format is like 0-3, 8-11, 14,17.

Values:         decimal list.



What:           /sys/devices/system/cpu/cpuX/topology/cluster_cpus

Description:    internal kernel map of CPUs within the same cluster.

Values:         hexadecimal bitmask.



What:           /sys/devices/system/cpu/cpuX/topology/cluster_cpus_list

Description:    human-readable list of CPUs within the same cluster.

                The format is like 0-3, 8-11, 14,17.

Values:         decimal list.



What:           /sys/devices/system/cpu/cpuX/topology/book_siblings

Description:    internal kernel map of cpuX's hardware threads within the same

                book_id. it's only used on s390.

Documentation/admin-guide/cgroup-v2.rst

+8 −0
Original line number Diff line number Diff line
@@ -1016,6 +1016,8 @@ All time durations are in microseconds. 
	- nr_periods

	- nr_throttled

	- throttled_usec

	- nr_bursts

	- burst_usec



  cpu.weight

	A read-write single value file which exists on non-root
@@ -1047,6 +1049,12 @@ All time durations are in microseconds. 
	$PERIOD duration.  "max" for $MAX indicates no limit.  If only

	one number is written, $MAX is updated.



  cpu.max.burst

	A read-write single value file which exists on non-root

	cgroups.  The default is "0".



	The burst in the range [0, $MAX].



  cpu.pressure

	A read-write nested-keyed file.

Documentation/admin-guide/cputopology.rst

+8 −4
Original line number Diff line number Diff line
@@ -19,11 +19,13 @@ these macros in include/asm-XXX/topology.h:: 


	#define topology_physical_package_id(cpu)

	#define topology_die_id(cpu)

	#define topology_cluster_id(cpu)

	#define topology_core_id(cpu)

	#define topology_book_id(cpu)

	#define topology_drawer_id(cpu)

	#define topology_sibling_cpumask(cpu)

	#define topology_core_cpumask(cpu)

	#define topology_cluster_cpumask(cpu)

	#define topology_die_cpumask(cpu)

	#define topology_book_cpumask(cpu)

	#define topology_drawer_cpumask(cpu)
@@ -39,10 +41,12 @@ not defined by include/asm-XXX/topology.h: 


1) topology_physical_package_id: -1

2) topology_die_id: -1

3) topology_core_id: 0

4) topology_sibling_cpumask: just the given CPU

5) topology_core_cpumask: just the given CPU

6) topology_die_cpumask: just the given CPU

3) topology_cluster_id: -1

4) topology_core_id: 0

5) topology_sibling_cpumask: just the given CPU

6) topology_core_cpumask: just the given CPU

7) topology_cluster_cpumask: just the given CPU

8) topology_die_cpumask: just the given CPU



For architectures that don't support books (CONFIG_SCHED_BOOK) there are no

default definitions for topology_book_id() and topology_book_cpumask().

Documentation/scheduler/sched-bwc.rst

+75 −9
Original line number Diff line number Diff line
@@ -22,9 +22,52 @@ cfs_quota units at each period boundary. As threads consume this bandwidth it 
is transferred to cpu-local "silos" on a demand basis. The amount transferred

within each of these updates is tunable and described as the "slice".



Burst feature

-------------

This feature borrows time now against our future underrun, at the cost of

increased interference against the other system users. All nicely bounded.



Traditional (UP-EDF) bandwidth control is something like:



  (U = \Sum u_i) <= 1



This guaranteeds both that every deadline is met and that the system is

stable. After all, if U were > 1, then for every second of walltime,

we'd have to run more than a second of program time, and obviously miss

our deadline, but the next deadline will be further out still, there is

never time to catch up, unbounded fail.



The burst feature observes that a workload doesn't always executes the full

quota; this enables one to describe u_i as a statistical distribution.



For example, have u_i = {x,e}_i, where x is the p(95) and x+e p(100)

(the traditional WCET). This effectively allows u to be smaller,

increasing the efficiency (we can pack more tasks in the system), but at

the cost of missing deadlines when all the odds line up. However, it

does maintain stability, since every overrun must be paired with an

underrun as long as our x is above the average.



That is, suppose we have 2 tasks, both specify a p(95) value, then we

have a p(95)*p(95) = 90.25% chance both tasks are within their quota and

everything is good. At the same time we have a p(5)p(5) = 0.25% chance

both tasks will exceed their quota at the same time (guaranteed deadline

fail). Somewhere in between there's a threshold where one exceeds and

the other doesn't underrun enough to compensate; this depends on the

specific CDFs.



At the same time, we can say that the worst case deadline miss, will be

\Sum e_i; that is, there is a bounded tardiness (under the assumption

that x+e is indeed WCET).



The interferenece when using burst is valued by the possibilities for

missing the deadline and the average WCET. Test results showed that when

there many cgroups or CPU is under utilized, the interference is

limited. More details are shown in:

https://lore.kernel.org/lkml/5371BD36-55AE-4F71-B9D7-B86DC32E3D2B@linux.alibaba.com/



Management

----------

Quota and period are managed within the cpu subsystem via cgroupfs.

Quota, period and burst are managed within the cpu subsystem via cgroupfs.



.. note::

   The cgroupfs files described in this section are only applicable
@@ -32,29 +75,37 @@ Quota and period are managed within the cpu subsystem via cgroupfs. 
   :ref:`Documentation/admin-guide/cgroup-v2.rst <cgroup-v2-cpu>`.



- cpu.cfs_quota_us: the total available run-time within a period (in

  microseconds)

- cpu.cfs_quota_us: run-time replenished within a period (in microseconds)

- cpu.cfs_period_us: the length of a period (in microseconds)

- cpu.stat: exports throttling statistics [explained further below]

- cpu.cfs_burst_us: the maximum accumulated run-time (in microseconds)



The default values are::



	cpu.cfs_period_us=100ms

	cpu.cfs_quota=-1

	cpu.cfs_quota_us=-1

	cpu.cfs_burst_us=0



A value of -1 for cpu.cfs_quota_us indicates that the group does not have any

bandwidth restriction in place, such a group is described as an unconstrained

bandwidth group. This represents the traditional work-conserving behavior for

CFS.



Writing any (valid) positive value(s) will enact the specified bandwidth limit.

The minimum quota allowed for the quota or period is 1ms. There is also an

upper bound on the period length of 1s. Additional restrictions exist when

bandwidth limits are used in a hierarchical fashion, these are explained in

more detail below.

Writing any (valid) positive value(s) no smaller than cpu.cfs_burst_us will

enact the specified bandwidth limit. The minimum quota allowed for the quota or

period is 1ms. There is also an upper bound on the period length of 1s.

Additional restrictions exist when bandwidth limits are used in a hierarchical

fashion, these are explained in more detail below.



Writing any negative value to cpu.cfs_quota_us will remove the bandwidth limit

and return the group to an unconstrained state once more.



A value of 0 for cpu.cfs_burst_us indicates that the group can not accumulate

any unused bandwidth. It makes the traditional bandwidth control behavior for

CFS unchanged. Writing any (valid) positive value(s) no larger than

cpu.cfs_quota_us into cpu.cfs_burst_us will enact the cap on unused bandwidth

accumulation.



Any updates to a group's bandwidth specification will result in it becoming

unthrottled if it is in a constrained state.
@@ -74,7 +125,7 @@ for more fine-grained consumption. 


Statistics

----------

A group's bandwidth statistics are exported via 3 fields in cpu.stat.

A group's bandwidth statistics are exported via 5 fields in cpu.stat.



cpu.stat:
@@ -82,6 +133,9 @@ cpu.stat: 
- nr_throttled: Number of times the group has been throttled/limited.

- throttled_time: The total time duration (in nanoseconds) for which entities

  of the group have been throttled.

- nr_bursts: Number of periods burst occurs.

- burst_time: Cumulative wall-time (in nanoseconds) that any CPUs has used

  above quota in respective periods



This interface is read-only.
@@ -179,3 +233,15 @@ Examples 


   By using a small period here we are ensuring a consistent latency

   response at the expense of burst capacity.



4. Limit a group to 40% of 1 CPU, and allow accumulate up to 20% of 1 CPU

   additionally, in case accumulation has been done.



   With 50ms period, 20ms quota will be equivalent to 40% of 1 CPU.

   And 10ms burst will be equivalent to 20% of 1 CPU.



	# echo 20000 > cpu.cfs_quota_us /* quota = 20ms */

	# echo 50000 > cpu.cfs_period_us /* period = 50ms */

	# echo 10000 > cpu.cfs_burst_us /* burst = 10ms */



   Larger buffer setting (no larger than quota) allows greater burst capacity.

arch/alpha/include/asm/processor.h

+1 −1
Original line number Diff line number Diff line
@@ -42,7 +42,7 @@ extern void start_thread(struct pt_regs *, unsigned long, unsigned long); 
struct task_struct;

extern void release_thread(struct task_struct *);



unsigned long get_wchan(struct task_struct *p);

unsigned long __get_wchan(struct task_struct *p);



#define KSTK_EIP(tsk) (task_pt_regs(tsk)->pc)