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| author | Tejun Heo <tj@kernel.org> | 2023-05-18 05:02:08 +0200 |
|---|---|---|
| committer | Tejun Heo <tj@kernel.org> | 2023-05-18 05:02:08 +0200 |
| commit | 616db8779b1e3f93075df691432cccc5ef3c3ba0 (patch) | |
| tree | 0dbc61931da6d05b333f2c8021fee79c2c294ac7 /Documentation/core-api | |
| parent | workqueue: Improve locking rule description for worker fields (diff) | |
| download | linux-616db8779b1e3f93075df691432cccc5ef3c3ba0.tar.xz linux-616db8779b1e3f93075df691432cccc5ef3c3ba0.zip | |
workqueue: Automatically mark CPU-hogging work items CPU_INTENSIVE
If a per-cpu work item hogs the CPU, it can prevent other work items from
starting through concurrency management. A per-cpu workqueue which intends
to host such CPU-hogging work items can choose to not participate in
concurrency management by setting %WQ_CPU_INTENSIVE; however, this can be
error-prone and difficult to debug when missed.
This patch adds an automatic CPU usage based detection. If a
concurrency-managed work item consumes more CPU time than the threshold
(10ms by default) continuously without intervening sleeps, wq_worker_tick()
which is called from scheduler_tick() will detect the condition and
automatically mark it CPU_INTENSIVE.
The mechanism isn't foolproof:
* Detection depends on tick hitting the work item. Getting preempted at the
right timings may allow a violating work item to evade detection at least
temporarily.
* nohz_full CPUs may not be running ticks and thus can fail detection.
* Even when detection is working, the 10ms detection delays can add up if
many CPU-hogging work items are queued at the same time.
However, in vast majority of cases, this should be able to detect violations
reliably and provide reasonable protection with a small increase in code
complexity.
If some work items trigger this condition repeatedly, the bigger problem
likely is the CPU being saturated with such per-cpu work items and the
solution would be making them UNBOUND. The next patch will add a debug
mechanism to help spot such cases.
v4: Documentation for workqueue.cpu_intensive_thresh_us added to
kernel-parameters.txt.
v3: Switch to use wq_worker_tick() instead of hooking into preemptions as
suggested by Peter.
v2: Lai pointed out that wq_worker_stopping() also needs to be called from
preemption and rtlock paths and an earlier patch was updated
accordingly. This patch adds a comment describing the risk of infinte
recursions and how they're avoided.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Diffstat (limited to 'Documentation/core-api')
| -rw-r--r-- | Documentation/core-api/workqueue.rst | 38 |
1 files changed, 19 insertions, 19 deletions
diff --git a/Documentation/core-api/workqueue.rst b/Documentation/core-api/workqueue.rst index 7e5c39310bbf..a389f31b025c 100644 --- a/Documentation/core-api/workqueue.rst +++ b/Documentation/core-api/workqueue.rst @@ -354,25 +354,25 @@ Monitoring Use tools/workqueue/wq_monitor.py to monitor workqueue operations: :: $ tools/workqueue/wq_monitor.py events - total infl CMwake mayday rescued - events 18545 0 5 - - - events_highpri 8 0 0 - - - events_long 3 0 0 - - - events_unbound 38306 0 - - - - events_freezable 0 0 0 - - - events_power_efficient 29598 0 0 - - - events_freezable_power_ 10 0 0 - - - sock_diag_events 0 0 0 - - - - total infl CMwake mayday rescued - events 18548 0 5 - - - events_highpri 8 0 0 - - - events_long 3 0 0 - - - events_unbound 38322 0 - - - - events_freezable 0 0 0 - - - events_power_efficient 29603 0 0 - - - events_freezable_power_ 10 0 0 - - - sock_diag_events 0 0 0 - - + total infl CPUitsv CMwake mayday rescued + events 18545 0 0 5 - - + events_highpri 8 0 0 0 - - + events_long 3 0 0 0 - - + events_unbound 38306 0 - - - - + events_freezable 0 0 0 0 - - + events_power_efficient 29598 0 0 0 - - + events_freezable_power_ 10 0 0 0 - - + sock_diag_events 0 0 0 0 - - + + total infl CPUitsv CMwake mayday rescued + events 18548 0 0 5 - - + events_highpri 8 0 0 0 - - + events_long 3 0 0 0 - - + events_unbound 38322 0 - - - - + events_freezable 0 0 0 0 - - + events_power_efficient 29603 0 0 0 - - + events_freezable_power_ 10 0 0 0 - - + sock_diag_events 0 0 0 0 - - ... |