Commit bd30fe6a authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge tag 'wq-for-6.6' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq 

Pull workqueue updates from Tejun Heo:

 - Unbound workqueues now support more flexible affinity scopes.

   The default behavior is to soft-affine according to last level cache
   boundaries. A work item queued from a given LLC is executed by a
   worker running on the same LLC but the worker may be moved across
   cache boundaries as the scheduler sees fit. On machines which
   multiple L3 caches, which are becoming more popular along with
   chiplet designs, this improves cache locality while not harming work
   conservation too much.

   Unbound workqueues are now also a lot more flexible in terms of
   execution affinity. Differeing levels of affinity scopes are
   supported and both the default and per-workqueue affinity settings
   can be modified dynamically. This should help working around amny of
   sub-optimal behaviors observed recently with asymmetric ARM CPUs.

   This involved signficant restructuring of workqueue code. Nothing was
   reported yet but there's some risk of subtle regressions. Should keep
   an eye out.

 - Rescuer workers now has more identifiable comms.

 - workqueue.unbound_cpus added so that CPUs which can be used by
   workqueue can be constrained early during boot.

 - Now that all the in-tree users have been flushed out, trigger warning
   if system-wide workqueues are flushed.

* tag 'wq-for-6.6' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq: (31 commits)
  workqueue: fix data race with the pwq->stats[] increment
  workqueue: Rename rescuer kworker
  workqueue: Make default affinity_scope dynamically updatable
  workqueue: Add "Affinity Scopes and Performance" section to documentation
  workqueue: Implement non-strict affinity scope for unbound workqueues
  workqueue: Add workqueue_attrs->__pod_cpumask
  workqueue: Factor out need_more_worker() check and worker wake-up
  workqueue: Factor out work to worker assignment and collision handling
  workqueue: Add multiple affinity scopes and interface to select them
  workqueue: Modularize wq_pod_type initialization
  workqueue: Add tools/workqueue/wq_dump.py which prints out workqueue configuration
  workqueue: Generalize unbound CPU pods
  workqueue: Factor out clearing of workqueue-only attrs fields
  workqueue: Factor out actual cpumask calculation to reduce subtlety in wq_update_pod()
  workqueue: Initialize unbound CPU pods later in the boot
  workqueue: Move wq_pod_init() below workqueue_init()
  workqueue: Rename NUMA related names to use pod instead
  workqueue: Rename workqueue_attrs->no_numa to ->ordered
  workqueue: Make unbound workqueues to use per-cpu pool_workqueues
  workqueue: Call wq_update_unbound_numa() on all CPUs in NUMA node on CPU hotplug
  ...
parents 7716f383 fe48ba7d

Documentation/admin-guide/kernel-parameters.txt

+19 −9
Original line number Diff line number Diff line
@@ -7076,6 +7076,13 @@ 
			disables both lockup detectors. Default is 10

			seconds.



	workqueue.unbound_cpus=

			[KNL,SMP] Specify to constrain one or some CPUs

			to use in unbound workqueues.

			Format: <cpu-list>

			By default, all online CPUs are available for

			unbound workqueues.



	workqueue.watchdog_thresh=

			If CONFIG_WQ_WATCHDOG is configured, workqueue can

			warn stall conditions and dump internal state to
@@ -7097,15 +7104,6 @@ 
			threshold repeatedly. They are likely good

			candidates for using WQ_UNBOUND workqueues instead.



	workqueue.disable_numa

			By default, all work items queued to unbound

			workqueues are affine to the NUMA nodes they're

			issued on, which results in better behavior in

			general.  If NUMA affinity needs to be disabled for

			whatever reason, this option can be used.  Note

			that this also can be controlled per-workqueue for

			workqueues visible under /sys/bus/workqueue/.



	workqueue.power_efficient

			Per-cpu workqueues are generally preferred because

			they show better performance thanks to cache
@@ -7121,6 +7119,18 @@ 
			The default value of this parameter is determined by

			the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.



        workqueue.default_affinity_scope=

			Select the default affinity scope to use for unbound

			workqueues. Can be one of "cpu", "smt", "cache",

			"numa" and "system". Default is "cache". For more

			information, see the Affinity Scopes section in

			Documentation/core-api/workqueue.rst.



			This can be changed after boot by writing to the

			matching /sys/module/workqueue/parameters file. All

			workqueues with the "default" affinity scope will be

			updated accordignly.



	workqueue.debug_force_rr_cpu

			Workqueue used to implicitly guarantee that work

			items queued without explicit CPU specified are put

Documentation/core-api/workqueue.rst

+337 −19
Original line number Diff line number Diff line 
====================================

Concurrency Managed Workqueue (cmwq)

====================================

=========

Workqueue

=========



:Date: September, 2010

:Author: Tejun Heo <tj@kernel.org>
@@ -25,8 +25,8 @@ there is no work item left on the workqueue the worker becomes idle. 
When a new work item gets queued, the worker begins executing again.





Why cmwq?

=========

Why Concurrency Managed Workqueue?

==================================



In the original wq implementation, a multi threaded (MT) wq had one

worker thread per CPU and a single threaded (ST) wq had one worker
@@ -220,17 +220,16 @@ resources, scheduled and executed. 
``max_active``

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



``@max_active`` determines the maximum number of execution contexts

per CPU which can be assigned to the work items of a wq.  For example,

with ``@max_active`` of 16, at most 16 work items of the wq can be

executing at the same time per CPU.

``@max_active`` determines the maximum number of execution contexts per

CPU which can be assigned to the work items of a wq. For example, with

``@max_active`` of 16, at most 16 work items of the wq can be executing

at the same time per CPU. This is always a per-CPU attribute, even for

unbound workqueues.



Currently, for a bound wq, the maximum limit for ``@max_active`` is

512 and the default value used when 0 is specified is 256.  For an

unbound wq, the limit is higher of 512 and 4 *

``num_possible_cpus()``.  These values are chosen sufficiently high

such that they are not the limiting factor while providing protection

in runaway cases.

The maximum limit for ``@max_active`` is 512 and the default value used

when 0 is specified is 256. These values are chosen sufficiently high

such that they are not the limiting factor while providing protection in

runaway cases.



The number of active work items of a wq is usually regulated by the

users of the wq, more specifically, by how many work items the users
@@ -348,27 +347,346 @@ Guidelines 
  level of locality in wq operations and work item execution.





Affinity Scopes

===============



An unbound workqueue groups CPUs according to its affinity scope to improve

cache locality. For example, if a workqueue is using the default affinity

scope of "cache", it will group CPUs according to last level cache

boundaries. A work item queued on the workqueue will be assigned to a worker

on one of the CPUs which share the last level cache with the issuing CPU.

Once started, the worker may or may not be allowed to move outside the scope

depending on the ``affinity_strict`` setting of the scope.



Workqueue currently supports the following affinity scopes.



``default``

  Use the scope in module parameter ``workqueue.default_affinity_scope``

  which is always set to one of the scopes below.



``cpu``

  CPUs are not grouped. A work item issued on one CPU is processed by a

  worker on the same CPU. This makes unbound workqueues behave as per-cpu

  workqueues without concurrency management.



``smt``

  CPUs are grouped according to SMT boundaries. This usually means that the

  logical threads of each physical CPU core are grouped together.



``cache``

  CPUs are grouped according to cache boundaries. Which specific cache

  boundary is used is determined by the arch code. L3 is used in a lot of

  cases. This is the default affinity scope.



``numa``

  CPUs are grouped according to NUMA bounaries.



``system``

  All CPUs are put in the same group. Workqueue makes no effort to process a

  work item on a CPU close to the issuing CPU.



The default affinity scope can be changed with the module parameter

``workqueue.default_affinity_scope`` and a specific workqueue's affinity

scope can be changed using ``apply_workqueue_attrs()``.



If ``WQ_SYSFS`` is set, the workqueue will have the following affinity scope

related interface files under its ``/sys/devices/virtual/WQ_NAME/``

directory.



``affinity_scope``

  Read to see the current affinity scope. Write to change.



  When default is the current scope, reading this file will also show the

  current effective scope in parentheses, for example, ``default (cache)``.



``affinity_strict``

  0 by default indicating that affinity scopes are not strict. When a work

  item starts execution, workqueue makes a best-effort attempt to ensure

  that the worker is inside its affinity scope, which is called

  repatriation. Once started, the scheduler is free to move the worker

  anywhere in the system as it sees fit. This enables benefiting from scope

  locality while still being able to utilize other CPUs if necessary and

  available.



  If set to 1, all workers of the scope are guaranteed always to be in the

  scope. This may be useful when crossing affinity scopes has other

  implications, for example, in terms of power consumption or workload

  isolation. Strict NUMA scope can also be used to match the workqueue

  behavior of older kernels.





Affinity Scopes and Performance

===============================



It'd be ideal if an unbound workqueue's behavior is optimal for vast

majority of use cases without further tuning. Unfortunately, in the current

kernel, there exists a pronounced trade-off between locality and utilization

necessitating explicit configurations when workqueues are heavily used.



Higher locality leads to higher efficiency where more work is performed for

the same number of consumed CPU cycles. However, higher locality may also

cause lower overall system utilization if the work items are not spread

enough across the affinity scopes by the issuers. The following performance

testing with dm-crypt clearly illustrates this trade-off.



The tests are run on a CPU with 12-cores/24-threads split across four L3

caches (AMD Ryzen 9 3900x). CPU clock boost is turned off for consistency.

``/dev/dm-0`` is a dm-crypt device created on NVME SSD (Samsung 990 PRO) and

opened with ``cryptsetup`` with default settings.





Scenario 1: Enough issuers and work spread across the machine

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



The command used: ::



  $ fio --filename=/dev/dm-0 --direct=1 --rw=randrw --bs=32k --ioengine=libaio \

    --iodepth=64 --runtime=60 --numjobs=24 --time_based --group_reporting \

    --name=iops-test-job --verify=sha512



There are 24 issuers, each issuing 64 IOs concurrently. ``--verify=sha512``

makes ``fio`` generate and read back the content each time which makes

execution locality matter between the issuer and ``kcryptd``. The followings

are the read bandwidths and CPU utilizations depending on different affinity

scope settings on ``kcryptd`` measured over five runs. Bandwidths are in

MiBps, and CPU util in percents.



.. list-table::

   :widths: 16 20 20

   :header-rows: 1



   * - Affinity

     - Bandwidth (MiBps)

     - CPU util (%)



   * - system

     - 1159.40 ±1.34

     - 99.31 ±0.02



   * - cache

     - 1166.40 ±0.89

     - 99.34 ±0.01



   * - cache (strict)

     - 1166.00 ±0.71

     - 99.35 ±0.01



With enough issuers spread across the system, there is no downside to

"cache", strict or otherwise. All three configurations saturate the whole

machine but the cache-affine ones outperform by 0.6% thanks to improved

locality.





Scenario 2: Fewer issuers, enough work for saturation

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



The command used: ::



  $ fio --filename=/dev/dm-0 --direct=1 --rw=randrw --bs=32k \

    --ioengine=libaio --iodepth=64 --runtime=60 --numjobs=8 \

    --time_based --group_reporting --name=iops-test-job --verify=sha512



The only difference from the previous scenario is ``--numjobs=8``. There are

a third of the issuers but is still enough total work to saturate the

system.



.. list-table::

   :widths: 16 20 20

   :header-rows: 1



   * - Affinity

     - Bandwidth (MiBps)

     - CPU util (%)



   * - system

     - 1155.40 ±0.89

     - 97.41 ±0.05



   * - cache

     - 1154.40 ±1.14

     - 96.15 ±0.09



   * - cache (strict)

     - 1112.00 ±4.64

     - 93.26 ±0.35



This is more than enough work to saturate the system. Both "system" and

"cache" are nearly saturating the machine but not fully. "cache" is using

less CPU but the better efficiency puts it at the same bandwidth as

"system".



Eight issuers moving around over four L3 cache scope still allow "cache

(strict)" to mostly saturate the machine but the loss of work conservation

is now starting to hurt with 3.7% bandwidth loss.





Scenario 3: Even fewer issuers, not enough work to saturate

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



The command used: ::



  $ fio --filename=/dev/dm-0 --direct=1 --rw=randrw --bs=32k \

    --ioengine=libaio --iodepth=64 --runtime=60 --numjobs=4 \

    --time_based --group_reporting --name=iops-test-job --verify=sha512



Again, the only difference is ``--numjobs=4``. With the number of issuers

reduced to four, there now isn't enough work to saturate the whole system

and the bandwidth becomes dependent on completion latencies.



.. list-table::

   :widths: 16 20 20

   :header-rows: 1



   * - Affinity

     - Bandwidth (MiBps)

     - CPU util (%)



   * - system

     - 993.60 ±1.82

     - 75.49 ±0.06



   * - cache

     - 973.40 ±1.52

     - 74.90 ±0.07



   * - cache (strict)

     - 828.20 ±4.49

     - 66.84 ±0.29



Now, the tradeoff between locality and utilization is clearer. "cache" shows

2% bandwidth loss compared to "system" and "cache (struct)" whopping 20%.





Conclusion and Recommendations

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



In the above experiments, the efficiency advantage of the "cache" affinity

scope over "system" is, while consistent and noticeable, small. However, the

impact is dependent on the distances between the scopes and may be more

pronounced in processors with more complex topologies.



While the loss of work-conservation in certain scenarios hurts, it is a lot

better than "cache (strict)" and maximizing workqueue utilization is

unlikely to be the common case anyway. As such, "cache" is the default

affinity scope for unbound pools.



* As there is no one option which is great for most cases, workqueue usages

  that may consume a significant amount of CPU are recommended to configure

  the workqueues using ``apply_workqueue_attrs()`` and/or enable

  ``WQ_SYSFS``.



* An unbound workqueue with strict "cpu" affinity scope behaves the same as

  ``WQ_CPU_INTENSIVE`` per-cpu workqueue. There is no real advanage to the

  latter and an unbound workqueue provides a lot more flexibility.



* Affinity scopes are introduced in Linux v6.5. To emulate the previous

  behavior, use strict "numa" affinity scope.



* The loss of work-conservation in non-strict affinity scopes is likely

  originating from the scheduler. There is no theoretical reason why the

  kernel wouldn't be able to do the right thing and maintain

  work-conservation in most cases. As such, it is possible that future

  scheduler improvements may make most of these tunables unnecessary.





Examining Configuration

=======================



Use tools/workqueue/wq_dump.py to examine unbound CPU affinity

configuration, worker pools and how workqueues map to the pools: ::



  $ tools/workqueue/wq_dump.py

  Affinity Scopes

  ===============

  wq_unbound_cpumask=0000000f



  CPU

    nr_pods  4

    pod_cpus [0]=00000001 [1]=00000002 [2]=00000004 [3]=00000008

    pod_node [0]=0 [1]=0 [2]=1 [3]=1

    cpu_pod  [0]=0 [1]=1 [2]=2 [3]=3



  SMT

    nr_pods  4

    pod_cpus [0]=00000001 [1]=00000002 [2]=00000004 [3]=00000008

    pod_node [0]=0 [1]=0 [2]=1 [3]=1

    cpu_pod  [0]=0 [1]=1 [2]=2 [3]=3



  CACHE (default)

    nr_pods  2

    pod_cpus [0]=00000003 [1]=0000000c

    pod_node [0]=0 [1]=1

    cpu_pod  [0]=0 [1]=0 [2]=1 [3]=1



  NUMA

    nr_pods  2

    pod_cpus [0]=00000003 [1]=0000000c

    pod_node [0]=0 [1]=1

    cpu_pod  [0]=0 [1]=0 [2]=1 [3]=1



  SYSTEM

    nr_pods  1

    pod_cpus [0]=0000000f

    pod_node [0]=-1

    cpu_pod  [0]=0 [1]=0 [2]=0 [3]=0



  Worker Pools

  ============

  pool[00] ref= 1 nice=  0 idle/workers=  4/  4 cpu=  0

  pool[01] ref= 1 nice=-20 idle/workers=  2/  2 cpu=  0

  pool[02] ref= 1 nice=  0 idle/workers=  4/  4 cpu=  1

  pool[03] ref= 1 nice=-20 idle/workers=  2/  2 cpu=  1

  pool[04] ref= 1 nice=  0 idle/workers=  4/  4 cpu=  2

  pool[05] ref= 1 nice=-20 idle/workers=  2/  2 cpu=  2

  pool[06] ref= 1 nice=  0 idle/workers=  3/  3 cpu=  3

  pool[07] ref= 1 nice=-20 idle/workers=  2/  2 cpu=  3

  pool[08] ref=42 nice=  0 idle/workers=  6/  6 cpus=0000000f

  pool[09] ref=28 nice=  0 idle/workers=  3/  3 cpus=00000003

  pool[10] ref=28 nice=  0 idle/workers= 17/ 17 cpus=0000000c

  pool[11] ref= 1 nice=-20 idle/workers=  1/  1 cpus=0000000f

  pool[12] ref= 2 nice=-20 idle/workers=  1/  1 cpus=00000003

  pool[13] ref= 2 nice=-20 idle/workers=  1/  1 cpus=0000000c



  Workqueue CPU -> pool

  =====================

  [    workqueue \ CPU              0  1  2  3 dfl]

  events                   percpu   0  2  4  6

  events_highpri           percpu   1  3  5  7

  events_long              percpu   0  2  4  6

  events_unbound           unbound  9  9 10 10  8

  events_freezable         percpu   0  2  4  6

  events_power_efficient   percpu   0  2  4  6

  events_freezable_power_  percpu   0  2  4  6

  rcu_gp                   percpu   0  2  4  6

  rcu_par_gp               percpu   0  2  4  6

  slub_flushwq             percpu   0  2  4  6

  netns                    ordered  8  8  8  8  8

  ...



See the command's help message for more info.





Monitoring

==========



Use tools/workqueue/wq_monitor.py to monitor workqueue operations: ::



  $ tools/workqueue/wq_monitor.py events

                              total  infl  CPUtime  CPUhog  CMwake  mayday rescued

                              total  infl  CPUtime  CPUhog CMW/RPR  mayday rescued

  events                      18545     0      6.1       0       5       -       -

  events_highpri                  8     0      0.0       0       0       -       -

  events_long                     3     0      0.0       0       0       -       -

  events_unbound              38306     0      0.1       -       -       -       -

  events_unbound              38306     0      0.1       -       7       -       -

  events_freezable                0     0      0.0       0       0       -       -

  events_power_efficient      29598     0      0.2       0       0       -       -

  events_freezable_power_        10     0      0.0       0       0       -       -

  sock_diag_events                0     0      0.0       0       0       -       -



                              total  infl  CPUtime  CPUhog  CMwake  mayday rescued

                              total  infl  CPUtime  CPUhog CMW/RPR  mayday rescued

  events                      18548     0      6.1       0       5       -       -

  events_highpri                  8     0      0.0       0       0       -       -

  events_long                     3     0      0.0       0       0       -       -

  events_unbound              38322     0      0.1       -       -       -       -

  events_unbound              38322     0      0.1       -       7       -       -

  events_freezable                0     0      0.0       0       0       -       -

  events_power_efficient      29603     0      0.2       0       0       -       -

  events_freezable_power_        10     0      0.0       0       0       -       -

include/linux/workqueue.h

+63 −52
Original line number Diff line number Diff line
@@ -125,6 +125,17 @@ struct rcu_work { 
	struct workqueue_struct *wq;

};



enum wq_affn_scope {

	WQ_AFFN_DFL,			/* use system default */

	WQ_AFFN_CPU,			/* one pod per CPU */

	WQ_AFFN_SMT,			/* one pod poer SMT */

	WQ_AFFN_CACHE,			/* one pod per LLC */

	WQ_AFFN_NUMA,			/* one pod per NUMA node */

	WQ_AFFN_SYSTEM,			/* one pod across the whole system */



	WQ_AFFN_NR_TYPES,

};



/**

 * struct workqueue_attrs - A struct for workqueue attributes.

 *
@@ -138,17 +149,58 @@ struct workqueue_attrs { 


	/**

	 * @cpumask: allowed CPUs

	 *

	 * Work items in this workqueue are affine to these CPUs and not allowed

	 * to execute on other CPUs. A pool serving a workqueue must have the

	 * same @cpumask.

	 */

	cpumask_var_t cpumask;



	/**

	 * @no_numa: disable NUMA affinity

	 * @__pod_cpumask: internal attribute used to create per-pod pools

	 *

	 * Internal use only.

	 *

	 * Per-pod unbound worker pools are used to improve locality. Always a

	 * subset of ->cpumask. A workqueue can be associated with multiple

	 * worker pools with disjoint @__pod_cpumask's. Whether the enforcement

	 * of a pool's @__pod_cpumask is strict depends on @affn_strict.

	 */

	cpumask_var_t __pod_cpumask;



	/**

	 * @affn_strict: affinity scope is strict

	 *

	 * Unlike other fields, ``no_numa`` isn't a property of a worker_pool. It

	 * only modifies how :c:func:`apply_workqueue_attrs` select pools and thus

	 * doesn't participate in pool hash calculations or equality comparisons.

	 * If clear, workqueue will make a best-effort attempt at starting the

	 * worker inside @__pod_cpumask but the scheduler is free to migrate it

	 * outside.

	 *

	 * If set, workers are only allowed to run inside @__pod_cpumask.

	 */

	bool affn_strict;



	/*

	 * Below fields aren't properties of a worker_pool. They only modify how

	 * :c:func:`apply_workqueue_attrs` select pools and thus don't

	 * participate in pool hash calculations or equality comparisons.

	 */



	/**

	 * @affn_scope: unbound CPU affinity scope

	 *

	 * CPU pods are used to improve execution locality of unbound work

	 * items. There are multiple pod types, one for each wq_affn_scope, and

	 * every CPU in the system belongs to one pod in every pod type. CPUs

	 * that belong to the same pod share the worker pool. For example,

	 * selecting %WQ_AFFN_NUMA makes the workqueue use a separate worker

	 * pool for each NUMA node.

	 */

	enum wq_affn_scope affn_scope;



	/**

	 * @ordered: work items must be executed one by one in queueing order

	 */

	bool no_numa;

	bool ordered;

};



static inline struct delayed_work *to_delayed_work(struct work_struct *work)
@@ -343,14 +395,10 @@ enum { 
	__WQ_ORDERED_EXPLICIT	= 1 << 19, /* internal: alloc_ordered_workqueue() */



	WQ_MAX_ACTIVE		= 512,	  /* I like 512, better ideas? */

	WQ_MAX_UNBOUND_PER_CPU	= 4,	  /* 4 * #cpus for unbound wq */

	WQ_UNBOUND_MAX_ACTIVE	= WQ_MAX_ACTIVE,

	WQ_DFL_ACTIVE		= WQ_MAX_ACTIVE / 2,

};



/* unbound wq's aren't per-cpu, scale max_active according to #cpus */

#define WQ_UNBOUND_MAX_ACTIVE	\

	max_t(int, WQ_MAX_ACTIVE, num_possible_cpus() * WQ_MAX_UNBOUND_PER_CPU)



/*

 * System-wide workqueues which are always present.

 *
@@ -391,7 +439,7 @@ extern struct workqueue_struct *system_freezable_power_efficient_wq; 
 * alloc_workqueue - allocate a workqueue

 * @fmt: printf format for the name of the workqueue

 * @flags: WQ_* flags

 * @max_active: max in-flight work items, 0 for default

 * @max_active: max in-flight work items per CPU, 0 for default

 * remaining args: args for @fmt

 *

 * Allocate a workqueue with the specified parameters.  For detailed
@@ -569,6 +617,7 @@ static inline bool schedule_work(struct work_struct *work) 


/*

 * Detect attempt to flush system-wide workqueues at compile time when possible.

 * Warn attempt to flush system-wide workqueues at runtime.

 *

 * See https://lkml.kernel.org/r/49925af7-78a8-a3dd-bce6-cfc02e1a9236@I-love.SAKURA.ne.jp

 * for reasons and steps for converting system-wide workqueues into local workqueues.
@@ -576,52 +625,13 @@ static inline bool schedule_work(struct work_struct *work) 
extern void __warn_flushing_systemwide_wq(void)

	__compiletime_warning("Please avoid flushing system-wide workqueues.");



/**

 * flush_scheduled_work - ensure that any scheduled work has run to completion.

 *

 * Forces execution of the kernel-global workqueue and blocks until its

 * completion.

 *

 * It's very easy to get into trouble if you don't take great care.

 * Either of the following situations will lead to deadlock:

 *

 *	One of the work items currently on the workqueue needs to acquire

 *	a lock held by your code or its caller.

 *

 *	Your code is running in the context of a work routine.

 *

 * They will be detected by lockdep when they occur, but the first might not

 * occur very often.  It depends on what work items are on the workqueue and

 * what locks they need, which you have no control over.

 *

 * In most situations flushing the entire workqueue is overkill; you merely

 * need to know that a particular work item isn't queued and isn't running.

 * In such cases you should use cancel_delayed_work_sync() or

 * cancel_work_sync() instead.

 *

 * Please stop calling this function! A conversion to stop flushing system-wide

 * workqueues is in progress. This function will be removed after all in-tree

 * users stopped calling this function.

 */

/*

 * The background of commit 771c035372a036f8 ("deprecate the

 * '__deprecated' attribute warnings entirely and for good") is that,

 * since Linus builds all modules between every single pull he does,

 * the standard kernel build needs to be _clean_ in order to be able to

 * notice when new problems happen. Therefore, don't emit warning while

 * there are in-tree users.

 */

/* Please stop using this function, for this function will be removed in near future. */

#define flush_scheduled_work()						\

({									\

	if (0)								\

	__warn_flushing_systemwide_wq();				\

	__flush_workqueue(system_wq);					\

})



/*

 * Although there is no longer in-tree caller, for now just emit warning

 * in order to give out-of-tree callers time to update.

 */

#define flush_workqueue(wq)						\

({									\

	struct workqueue_struct *_wq = (wq);				\
@@ -714,5 +724,6 @@ int workqueue_offline_cpu(unsigned int cpu); 


void __init workqueue_init_early(void);

void __init workqueue_init(void);

void __init workqueue_init_topology(void);



#endif

init/main.c

+1 −0
Original line number Diff line number Diff line
@@ -1540,6 +1540,7 @@ static noinline void __init kernel_init_freeable(void) 
	smp_init();

	sched_init_smp();



	workqueue_init_topology();

	padata_init();

	page_alloc_init_late();

kernel/workqueue.c

+901 −717

File changed.

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