Lines Matching +full:- +full:affinity
33 thread system-wide. A single MT wq needed to keep around the same
60 * Use per-CPU unified worker pools shared by all wq to provide
85 worker-pools.
87 The cmwq design differentiates between the user-facing workqueues that
89 which manages worker-pools and processes the queued work items.
91 There are two worker-pools, one for normal work items and the other
93 worker-pools to serve work items queued on unbound workqueues - the
98 Each per-CPU BH worker pool contains only one pseudo worker which represents
110 When a work item is queued to a workqueue, the target worker-pool is
112 and appended on the shared worklist of the worker-pool. For example,
114 be queued on the worklist of either normal or highpri worker-pool that
123 Each worker-pool bound to an actual CPU implements concurrency
124 management by hooking into the scheduler. The worker-pool is notified
130 workers on the CPU, the worker-pool doesn't start execution of a new
152 wq's that have a rescue-worker reserved for execution under memory
153 pressure. Else it is possible that the worker-pool deadlocks waiting
162 removal. ``alloc_workqueue()`` takes three arguments - ``@name``,
173 ---------
177 workqueues are always per-CPU and all BH work items are executed in the
188 worker-pools which host workers which are not bound to any
191 worker-pools try to start execution of work items as soon as
215 worker-pool of the target cpu. Highpri worker-pools are
218 Note that normal and highpri worker-pools don't interact with
226 worker-pool from starting execution. This is useful for bound
233 non-CPU-intensive work items can delay execution of CPU
240 --------------
245 at the same time per CPU. This is always a per-CPU attribute, even for
370 Affinity Scopes
373 An unbound workqueue groups CPUs according to its affinity scope to improve
374 cache locality. For example, if a workqueue is using the default affinity
381 Workqueue currently supports the following affinity scopes.
389 worker on the same CPU. This makes unbound workqueues behave as per-cpu
399 cases. This is the default affinity scope.
408 The default affinity scope can be changed with the module parameter
409 ``workqueue.default_affinity_scope`` and a specific workqueue's affinity
412 If ``WQ_SYSFS`` is set, the workqueue will have the following affinity scope
417 Read to see the current affinity scope. Write to change.
423 0 by default indicating that affinity scopes are not strict. When a work
424 item starts execution, workqueue makes a best-effort attempt to ensure
425 that the worker is inside its affinity scope, which is called
432 scope. This may be useful when crossing affinity scopes has other
438 Affinity Scopes and Performance
443 kernel, there exists a pronounced trade-off between locality and utilization
449 enough across the affinity scopes by the issuers. The following performance
450 testing with dm-crypt clearly illustrates this trade-off.
452 The tests are run on a CPU with 12-cores/24-threads split across four L3
454 ``/dev/dm-0`` is a dm-crypt device created on NVME SSD (Samsung 990 PRO) and
459 -------------------------------------------------------------
463 $ fio --filename=/dev/dm-0 --direct=1 --rw=randrw --bs=32k --ioengine=libaio \
464 --iodepth=64 --runtime=60 --numjobs=24 --time_based --group_reporting \
465 --name=iops-test-job --verify=sha512
467 There are 24 issuers, each issuing 64 IOs concurrently. ``--verify=sha512``
470 are the read bandwidths and CPU utilizations depending on different affinity
474 .. list-table::
476 :header-rows: 1
478 * - Affinity
479 - Bandwidth (MiBps)
480 - CPU util (%)
482 * - system
483 - 1159.40 ±1.34
484 - 99.31 ±0.02
486 * - cache
487 - 1166.40 ±0.89
488 - 99.34 ±0.01
490 * - cache (strict)
491 - 1166.00 ±0.71
492 - 99.35 ±0.01
496 machine but the cache-affine ones outperform by 0.6% thanks to improved
501 -----------------------------------------------------
505 $ fio --filename=/dev/dm-0 --direct=1 --rw=randrw --bs=32k \
506 --ioengine=libaio --iodepth=64 --runtime=60 --numjobs=8 \
507 --time_based --group_reporting --name=iops-test-job --verify=sha512
509 The only difference from the previous scenario is ``--numjobs=8``. There are
513 .. list-table::
515 :header-rows: 1
517 * - Affinity
518 - Bandwidth (MiBps)
519 - CPU util (%)
521 * - system
522 - 1155.40 ±0.89
523 - 97.41 ±0.05
525 * - cache
526 - 1154.40 ±1.14
527 - 96.15 ±0.09
529 * - cache (strict)
530 - 1112.00 ±4.64
531 - 93.26 ±0.35
544 -----------------------------------------------------------
548 $ fio --filename=/dev/dm-0 --direct=1 --rw=randrw --bs=32k \
549 --ioengine=libaio --iodepth=64 --runtime=60 --numjobs=4 \
550 --time_based --group_reporting --name=iops-test-job --verify=sha512
552 Again, the only difference is ``--numjobs=4``. With the number of issuers
556 .. list-table::
558 :header-rows: 1
560 * - Affinity
561 - Bandwidth (MiBps)
562 - CPU util (%)
564 * - system
565 - 993.60 ±1.82
566 - 75.49 ±0.06
568 * - cache
569 - 973.40 ±1.52
570 - 74.90 ±0.07
572 * - cache (strict)
573 - 828.20 ±4.49
574 - 66.84 ±0.29
581 ------------------------------
583 In the above experiments, the efficiency advantage of the "cache" affinity
588 While the loss of work-conservation in certain scenarios hurts, it is a lot
591 affinity scope for unbound pools.
598 * An unbound workqueue with strict "cpu" affinity scope behaves the same as
599 ``WQ_CPU_INTENSIVE`` per-cpu workqueue. There is no real advanage to the
602 * Affinity scopes are introduced in Linux v6.5. To emulate the previous
603 behavior, use strict "numa" affinity scope.
605 * The loss of work-conservation in non-strict affinity scopes is likely
608 work-conservation in most cases. As such, it is possible that future
615 Use tools/workqueue/wq_dump.py to examine unbound CPU affinity
619 Affinity Scopes
650 pod_node [0]=-1
656 pool[01] ref= 1 nice=-20 idle/workers= 2/ 2 cpu= 0
658 pool[03] ref= 1 nice=-20 idle/workers= 2/ 2 cpu= 1
660 pool[05] ref= 1 nice=-20 idle/workers= 2/ 2 cpu= 2
662 pool[07] ref= 1 nice=-20 idle/workers= 2/ 2 cpu= 3
666 pool[11] ref= 1 nice=-20 idle/workers= 1/ 1 cpus=0000000f
667 pool[12] ref= 2 nice=-20 idle/workers= 1/ 1 cpus=00000003
668 pool[13] ref= 2 nice=-20 idle/workers= 1/ 1 cpus=0000000c
670 Workqueue CPU -> pool
696 events 18545 0 6.1 0 5 - -
697 events_highpri 8 0 0.0 0 0 - -
698 events_long 3 0 0.0 0 0 - -
699 events_unbound 38306 0 0.1 - 7 - -
700 events_freezable 0 0 0.0 0 0 - -
701 events_power_efficient 29598 0 0.2 0 0 - -
702 events_freezable_pwr_ef 10 0 0.0 0 0 - -
703 sock_diag_events 0 0 0.0 0 0 - -
706 events 18548 0 6.1 0 5 - -
707 events_highpri 8 0 0.0 0 0 - -
708 events_long 3 0 0.0 0 0 - -
709 events_unbound 38322 0 0.1 - 7 - -
710 events_freezable 0 0 0.0 0 0 - -
711 events_power_efficient 29603 0 0.2 0 0 - -
712 events_freezable_pwr_ef 10 0 0.0 0 0 - -
713 sock_diag_events 0 0 0.0 0 0 - -
760 Non-reentrance Conditions
763 Workqueue guarantees that a work item cannot be re-entrant if the following
771 executed by at most one worker system-wide at any given time.
781 .. kernel-doc:: include/linux/workqueue.h
783 .. kernel-doc:: kernel/workqueue.c