Hello,
The only meaningful change is the use of printk_deferred() in 0006 which was
posted in the v3 thread. I'm applying this version to wq/for-6.5. Posting
for the record.
v4: * 0006-workqueue-Report-work-funcs-that-trigger-automatic-C.patch
updated to use printk_deferred() instead of custom bouncing which was
broken and didn't resolve the deadlock possibility anyway.
* Documentation updates.
v3: * Switched to hooking into scheduler_tick() instead of scheduling paths
as suggested by Peter. It's less gnarly and works well in general;
however, as the mechanism is now sampling based, there can be
contrived cases where detection can be temporarily avoided. Also, it
wouldn't work on nohz_full CPUs. Neither is critical especially given
that common offenders are likely to be weeded out with the debug
reporting over time.
* As the above means that workqueue is no longer obersving all
scheduling events, it can't track the CPU time being consumed by the
workers on its own and thus can't use global clocks (e.g. jiffies).
The CPU time consumption tracking is still done with
p->se.sum_exec_runtime.
* The mechanism was incorrectly monitoring the entire CPU time a given
work item has consumed instead of each stretch without intervening
sleeps. Fixed.
* CPU time monitoring is now tick sampling based. The previous
p->se.sum_exec_runtime implementation was missing CPU time consumed
between the last scheduling event the work item finished and the
completion, so, e.g., work items that never schedule would always be
accounted as zero CPU time. While the sampling based implementation
isn't very accurate, this is good enough for getting the overall
picture of workqueues that consume a lot of CPU cycles.
* Patches reordered so that the visibility one can be applied first.
Documentation improved.
v2: * Lai pointed out that !SM_NONE cases should also be notified. 0001 and
0004 are updated accordingly.
* PeterZ suggested reporting on work items that trigger the auto CPU
intensive mechanism. 0006 adds reporting of work functions that
trigger the mechanism repeatedly with exponential backoff.
To reduce the number of concurrent worker threads, workqueue holds back
starting per-cpu work items while the previous work item stays in the
RUNNING state. As such a per-cpu work item which consumes a lot of CPU
cycles, even if it has cond_resched()'s in the right places, can stall other
per-cpu work items.
To support per-cpu work items that may occupy the CPU for a substantial
period of time, workqueue has WQ_CPU_INTENSIVE flag which exempts work items
issued through the marked workqueue from concurrency management - they're
started immediately and don't block other work items. While this works, it's
error-prone in that a workqueue user can easily forget to set the flag or
set it unnecessarily. Furthermore, the impacts of the wrong flag setting can
be rather indirect and challenging to root-cause.
This patchset makes workqueue auto-detect CPU intensive work items based on
CPU consumption. If a work item consumes more than the threshold (10ms by
default) of CPU time, it's automatically marked as CPU intensive when it
gets scheduled out which unblocks starting of pending per-cpu work items.
The mechanism isn't foolproof in that the detection delays can add up if
many CPU-hogging work items are queued at the same time. However, in such
situations, the bigger problem likely is the CPU being saturated with
per-cpu work items and the solution would be making them UNBOUND. Future
changes will make UNBOUND workqueues more attractive by improving their
locality behaviors and configurability. We might eventually remove the
explicit WQ_CPU_INTENSIVE flag.
While at it, add statistics and a monitoring script. Lack of visibility has
always been a bit of pain point when debugging workqueue related issues and
with this change and more drastic ones planned for workqueue, this is a good
time to address the shortcoming.
This patchset was born out of the discussion in the following thread:
https://lkml.kernel.org/r/CAHk-=wgE9kORADrDJ4nEsHHLirqPCZ1tGaEPAZejHdZ03qCOGg@mail.gmail.com
and contains the following patches:
0001-workqueue-Add-pwq-stats-and-a-monitoring-script.patch
0002-workqueue-Re-order-struct-worker-fields.patch
0003-workqueue-Move-worker_set-clr_flags-upwards.patch
0004-workqueue-Improve-locking-rule-description-for-worke.patch
0005-workqueue-Automatically-mark-CPU-hogging-work-items-.patch
0006-workqueue-Report-work-funcs-that-trigger-automatic-C.patch
0007-workqueue-Track-and-monitor-per-workqueue-CPU-time-u.patch
and also available in the following git branch:
git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq.git auto-cpu-intensive-v4
diffstat follows. Thanks.
Documentation/admin-guide/kernel-parameters.txt | 12 +
Documentation/core-api/workqueue.rst | 32 +++++
kernel/sched/core.c | 3
kernel/workqueue.c | 302 ++++++++++++++++++++++++++++++++++++++++----------
kernel/workqueue_internal.h | 24 ++-
lib/Kconfig.debug | 13 ++
tools/workqueue/wq_monitor.py | 168 +++++++++++++++++++++++++++
7 files changed, 483 insertions(+), 71 deletions(-)
--
tejun
They are going to be used in wq_worker_stopping(). Move them upwards.
Signed-off-by: Tejun Heo <[email protected]>
Cc: Lai Jiangshan <[email protected]>
---
kernel/workqueue.c | 108 ++++++++++++++++++++++-----------------------
1 file changed, 54 insertions(+), 54 deletions(-)
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 60d5b84cccb2..d70bb5be99ce 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -879,6 +879,60 @@ static void wake_up_worker(struct worker_pool *pool)
wake_up_process(worker->task);
}
+/**
+ * worker_set_flags - set worker flags and adjust nr_running accordingly
+ * @worker: self
+ * @flags: flags to set
+ *
+ * Set @flags in @worker->flags and adjust nr_running accordingly.
+ *
+ * CONTEXT:
+ * raw_spin_lock_irq(pool->lock)
+ */
+static inline void worker_set_flags(struct worker *worker, unsigned int flags)
+{
+ struct worker_pool *pool = worker->pool;
+
+ WARN_ON_ONCE(worker->task != current);
+
+ /* If transitioning into NOT_RUNNING, adjust nr_running. */
+ if ((flags & WORKER_NOT_RUNNING) &&
+ !(worker->flags & WORKER_NOT_RUNNING)) {
+ pool->nr_running--;
+ }
+
+ worker->flags |= flags;
+}
+
+/**
+ * worker_clr_flags - clear worker flags and adjust nr_running accordingly
+ * @worker: self
+ * @flags: flags to clear
+ *
+ * Clear @flags in @worker->flags and adjust nr_running accordingly.
+ *
+ * CONTEXT:
+ * raw_spin_lock_irq(pool->lock)
+ */
+static inline void worker_clr_flags(struct worker *worker, unsigned int flags)
+{
+ struct worker_pool *pool = worker->pool;
+ unsigned int oflags = worker->flags;
+
+ WARN_ON_ONCE(worker->task != current);
+
+ worker->flags &= ~flags;
+
+ /*
+ * If transitioning out of NOT_RUNNING, increment nr_running. Note
+ * that the nested NOT_RUNNING is not a noop. NOT_RUNNING is mask
+ * of multiple flags, not a single flag.
+ */
+ if ((flags & WORKER_NOT_RUNNING) && (oflags & WORKER_NOT_RUNNING))
+ if (!(worker->flags & WORKER_NOT_RUNNING))
+ pool->nr_running++;
+}
+
/**
* wq_worker_running - a worker is running again
* @task: task waking up
@@ -983,60 +1037,6 @@ work_func_t wq_worker_last_func(struct task_struct *task)
return worker->last_func;
}
-/**
- * worker_set_flags - set worker flags and adjust nr_running accordingly
- * @worker: self
- * @flags: flags to set
- *
- * Set @flags in @worker->flags and adjust nr_running accordingly.
- *
- * CONTEXT:
- * raw_spin_lock_irq(pool->lock)
- */
-static inline void worker_set_flags(struct worker *worker, unsigned int flags)
-{
- struct worker_pool *pool = worker->pool;
-
- WARN_ON_ONCE(worker->task != current);
-
- /* If transitioning into NOT_RUNNING, adjust nr_running. */
- if ((flags & WORKER_NOT_RUNNING) &&
- !(worker->flags & WORKER_NOT_RUNNING)) {
- pool->nr_running--;
- }
-
- worker->flags |= flags;
-}
-
-/**
- * worker_clr_flags - clear worker flags and adjust nr_running accordingly
- * @worker: self
- * @flags: flags to clear
- *
- * Clear @flags in @worker->flags and adjust nr_running accordingly.
- *
- * CONTEXT:
- * raw_spin_lock_irq(pool->lock)
- */
-static inline void worker_clr_flags(struct worker *worker, unsigned int flags)
-{
- struct worker_pool *pool = worker->pool;
- unsigned int oflags = worker->flags;
-
- WARN_ON_ONCE(worker->task != current);
-
- worker->flags &= ~flags;
-
- /*
- * If transitioning out of NOT_RUNNING, increment nr_running. Note
- * that the nested NOT_RUNNING is not a noop. NOT_RUNNING is mask
- * of multiple flags, not a single flag.
- */
- if ((flags & WORKER_NOT_RUNNING) && (oflags & WORKER_NOT_RUNNING))
- if (!(worker->flags & WORKER_NOT_RUNNING))
- pool->nr_running++;
-}
-
/**
* find_worker_executing_work - find worker which is executing a work
* @pool: pool of interest
--
2.40.1
* Some worker fields are modified only by the worker itself while holding
pool->lock thus making them safe to read from self, IRQ context if the CPU
is running the worker or while holding pool->lock. Add 'K' locking rule
for them.
* worker->sleeping is currently marked "None" which isn't very descriptive.
It's used only by the worker itself. Add 'S' locking rule for it.
A future patch will depend on the 'K' rule to access worker->current_* from
the scheduler ticks.
Signed-off-by: Tejun Heo <[email protected]>
---
kernel/workqueue.c | 6 ++++++
kernel/workqueue_internal.h | 15 ++++++++-------
2 files changed, 14 insertions(+), 7 deletions(-)
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index d70bb5be99ce..942421443603 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -126,6 +126,12 @@ enum {
* cpu or grabbing pool->lock is enough for read access. If
* POOL_DISASSOCIATED is set, it's identical to L.
*
+ * K: Only modified by worker while holding pool->lock. Can be safely read by
+ * self, while holding pool->lock or from IRQ context if %current is the
+ * kworker.
+ *
+ * S: Only modified by worker self.
+ *
* A: wq_pool_attach_mutex protected.
*
* PL: wq_pool_mutex protected.
diff --git a/kernel/workqueue_internal.h b/kernel/workqueue_internal.h
index 0600f04ceeb2..c2455be7b4c2 100644
--- a/kernel/workqueue_internal.h
+++ b/kernel/workqueue_internal.h
@@ -28,14 +28,15 @@ struct worker {
struct hlist_node hentry; /* L: while busy */
};
- struct work_struct *current_work; /* L: work being processed */
- work_func_t current_func; /* L: current_work's fn */
- struct pool_workqueue *current_pwq; /* L: current_work's pwq */
- unsigned int current_color; /* L: current_work's color */
- int sleeping; /* None */
+ struct work_struct *current_work; /* K: work being processed and its */
+ work_func_t current_func; /* K: function */
+ struct pool_workqueue *current_pwq; /* K: pwq */
+ unsigned int current_color; /* K: color */
+
+ int sleeping; /* S: is worker sleeping? */
/* used by the scheduler to determine a worker's last known identity */
- work_func_t last_func; /* L: last work's fn */
+ work_func_t last_func; /* K: last work's fn */
struct list_head scheduled; /* L: scheduled works */
@@ -45,7 +46,7 @@ struct worker {
struct list_head node; /* A: anchored at pool->workers */
/* A: runs through worker->node */
- unsigned long last_active; /* L: last active timestamp */
+ unsigned long last_active; /* K: last active timestamp */
unsigned int flags; /* X: flags */
int id; /* I: worker id */
--
2.40.1
Currently, the only way to peer into workqueue operations is through
tracing. While possible, it isn't easy or convenient to monitor
per-workqueue behaviors over time this way. Let's add pwq->stats[] that
track relevant events and a drgn monitoring script -
tools/workqueue/wq_monitor.py.
It's arguable whether this needs to be configurable. However, it currently
only has several counters and the runtime overhead shouldn't be noticeable
given that they're on pwq's which are per-cpu on per-cpu workqueues and
per-numa-node on unbound ones. Let's keep it simple for the time being.
v2: Patch reordered to earlier with fewer fields. Field will be added back
gradually. Help message improved.
Signed-off-by: Tejun Heo <[email protected]>
Cc: Lai Jiangshan <[email protected]>
---
Documentation/core-api/workqueue.rst | 32 ++++++
kernel/workqueue.c | 24 ++++-
tools/workqueue/wq_monitor.py | 150 +++++++++++++++++++++++++++
3 files changed, 205 insertions(+), 1 deletion(-)
create mode 100644 tools/workqueue/wq_monitor.py
diff --git a/Documentation/core-api/workqueue.rst b/Documentation/core-api/workqueue.rst
index 8ec4d6270b24..7e5c39310bbf 100644
--- a/Documentation/core-api/workqueue.rst
+++ b/Documentation/core-api/workqueue.rst
@@ -348,6 +348,37 @@ Guidelines
level of locality in wq operations and work item execution.
+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 - -
+
+ ...
+
+See the command's help message for more info.
+
+
Debugging
=========
@@ -387,6 +418,7 @@ For the second type of problems it should be possible to just check
The work item's function should be trivially visible in the stack
trace.
+
Non-reentrance Conditions
=========================
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 36bccc1285b3..60d5b84cccb2 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -199,6 +199,20 @@ struct worker_pool {
struct rcu_head rcu;
};
+/*
+ * Per-pool_workqueue statistics. These can be monitored using
+ * tools/workqueue/wq_monitor.py.
+ */
+enum pool_workqueue_stats {
+ PWQ_STAT_STARTED, /* work items started execution */
+ PWQ_STAT_COMPLETED, /* work items completed execution */
+ PWQ_STAT_CM_WAKEUP, /* concurrency-management worker wakeups */
+ PWQ_STAT_MAYDAY, /* maydays to rescuer */
+ PWQ_STAT_RESCUED, /* linked work items executed by rescuer */
+
+ PWQ_NR_STATS,
+};
+
/*
* The per-pool workqueue. While queued, the lower WORK_STRUCT_FLAG_BITS
* of work_struct->data are used for flags and the remaining high bits
@@ -236,6 +250,8 @@ struct pool_workqueue {
struct list_head pwqs_node; /* WR: node on wq->pwqs */
struct list_head mayday_node; /* MD: node on wq->maydays */
+ u64 stats[PWQ_NR_STATS];
+
/*
* Release of unbound pwq is punted to system_wq. See put_pwq()
* and pwq_unbound_release_workfn() for details. pool_workqueue
@@ -929,8 +945,10 @@ void wq_worker_sleeping(struct task_struct *task)
}
pool->nr_running--;
- if (need_more_worker(pool))
+ if (need_more_worker(pool)) {
+ worker->current_pwq->stats[PWQ_STAT_CM_WAKEUP]++;
wake_up_worker(pool);
+ }
raw_spin_unlock_irq(&pool->lock);
}
@@ -2165,6 +2183,7 @@ static void send_mayday(struct work_struct *work)
get_pwq(pwq);
list_add_tail(&pwq->mayday_node, &wq->maydays);
wake_up_process(wq->rescuer->task);
+ pwq->stats[PWQ_STAT_MAYDAY]++;
}
}
@@ -2403,6 +2422,7 @@ __acquires(&pool->lock)
* workqueues), so hiding them isn't a problem.
*/
lockdep_invariant_state(true);
+ pwq->stats[PWQ_STAT_STARTED]++;
trace_workqueue_execute_start(work);
worker->current_func(work);
/*
@@ -2410,6 +2430,7 @@ __acquires(&pool->lock)
* point will only record its address.
*/
trace_workqueue_execute_end(work, worker->current_func);
+ pwq->stats[PWQ_STAT_COMPLETED]++;
lock_map_release(&lockdep_map);
lock_map_release(&pwq->wq->lockdep_map);
@@ -2653,6 +2674,7 @@ static int rescuer_thread(void *__rescuer)
if (first)
pool->watchdog_ts = jiffies;
move_linked_works(work, scheduled, &n);
+ pwq->stats[PWQ_STAT_RESCUED]++;
}
first = false;
}
diff --git a/tools/workqueue/wq_monitor.py b/tools/workqueue/wq_monitor.py
new file mode 100644
index 000000000000..fc1643ba06b3
--- /dev/null
+++ b/tools/workqueue/wq_monitor.py
@@ -0,0 +1,150 @@
+#!/usr/bin/env drgn
+#
+# Copyright (C) 2023 Tejun Heo <[email protected]>
+# Copyright (C) 2023 Meta Platforms, Inc. and affiliates.
+
+desc = """
+This is a drgn script to monitor workqueues. For more info on drgn, visit
+https://github.com/osandov/drgn.
+
+ total Total number of work items executed by the workqueue.
+
+ infl The number of currently in-flight work items.
+
+ CMwake The number of concurrency-management wake-ups while executing a
+ work item of the workqueue.
+
+ mayday The number of times the rescuer was requested while waiting for
+ new worker creation.
+
+ rescued The number of work items executed by the rescuer.
+"""
+
+import sys
+import signal
+import os
+import re
+import time
+import json
+
+import drgn
+from drgn.helpers.linux.list import list_for_each_entry,list_empty
+from drgn.helpers.linux.cpumask import for_each_possible_cpu
+
+import argparse
+parser = argparse.ArgumentParser(description=desc,
+ formatter_class=argparse.RawTextHelpFormatter)
+parser.add_argument('workqueue', metavar='REGEX', nargs='*',
+ help='Target workqueue name patterns (all if empty)')
+parser.add_argument('-i', '--interval', metavar='SECS', type=float, default=1,
+ help='Monitoring interval (0 to print once and exit)')
+parser.add_argument('-j', '--json', action='store_true',
+ help='Output in json')
+args = parser.parse_args()
+
+def err(s):
+ print(s, file=sys.stderr, flush=True)
+ sys.exit(1)
+
+workqueues = prog['workqueues']
+
+WQ_UNBOUND = prog['WQ_UNBOUND']
+WQ_MEM_RECLAIM = prog['WQ_MEM_RECLAIM']
+
+PWQ_STAT_STARTED = prog['PWQ_STAT_STARTED'] # work items started execution
+PWQ_STAT_COMPLETED = prog['PWQ_STAT_COMPLETED'] # work items completed execution
+PWQ_STAT_CM_WAKEUP = prog['PWQ_STAT_CM_WAKEUP'] # concurrency-management worker wakeups
+PWQ_STAT_MAYDAY = prog['PWQ_STAT_MAYDAY'] # maydays to rescuer
+PWQ_STAT_RESCUED = prog['PWQ_STAT_RESCUED'] # linked work items executed by rescuer
+PWQ_NR_STATS = prog['PWQ_NR_STATS']
+
+class WqStats:
+ def __init__(self, wq):
+ self.name = wq.name.string_().decode()
+ self.unbound = wq.flags & WQ_UNBOUND != 0
+ self.mem_reclaim = wq.flags & WQ_MEM_RECLAIM != 0
+ self.stats = [0] * PWQ_NR_STATS
+ for pwq in list_for_each_entry('struct pool_workqueue', wq.pwqs.address_of_(), 'pwqs_node'):
+ for i in range(PWQ_NR_STATS):
+ self.stats[i] += int(pwq.stats[i])
+
+ def dict(self, now):
+ return { 'timestamp' : now,
+ 'name' : self.name,
+ 'unbound' : self.unbound,
+ 'mem_reclaim' : self.mem_reclaim,
+ 'started' : self.stats[PWQ_STAT_STARTED],
+ 'completed' : self.stats[PWQ_STAT_COMPLETED],
+ 'cm_wakeup' : self.stats[PWQ_STAT_CM_WAKEUP],
+ 'mayday' : self.stats[PWQ_STAT_MAYDAY],
+ 'rescued' : self.stats[PWQ_STAT_RESCUED], }
+
+ def table_header_str():
+ return f'{"":>24} {"total":>8} {"infl":>5} {"CMwake":>7} {"mayday":>7} {"rescued":>7}'
+
+ def table_row_str(self):
+ cm_wakeup = '-'
+ mayday = '-'
+ rescued = '-'
+
+ if not self.unbound:
+ cm_wakeup = str(self.stats[PWQ_STAT_CM_WAKEUP])
+
+ if self.mem_reclaim:
+ mayday = str(self.stats[PWQ_STAT_MAYDAY])
+ rescued = str(self.stats[PWQ_STAT_RESCUED])
+
+ out = f'{self.name[-24:]:24} ' \
+ f'{self.stats[PWQ_STAT_STARTED]:8} ' \
+ f'{max(self.stats[PWQ_STAT_STARTED] - self.stats[PWQ_STAT_COMPLETED], 0):5} ' \
+ f'{cm_wakeup:>7} ' \
+ f'{mayday:>7} ' \
+ f'{rescued:>7} '
+ return out.rstrip(':')
+
+exit_req = False
+
+def sigint_handler(signr, frame):
+ global exit_req
+ exit_req = True
+
+def main():
+ # handle args
+ table_fmt = not args.json
+ interval = args.interval
+
+ re_str = None
+ if args.workqueue:
+ for r in args.workqueue:
+ if re_str is None:
+ re_str = r
+ else:
+ re_str += '|' + r
+
+ filter_re = re.compile(re_str) if re_str else None
+
+ # monitoring loop
+ signal.signal(signal.SIGINT, sigint_handler)
+
+ while not exit_req:
+ now = time.time()
+
+ if table_fmt:
+ print()
+ print(WqStats.table_header_str())
+
+ for wq in list_for_each_entry('struct workqueue_struct', workqueues.address_of_(), 'list'):
+ stats = WqStats(wq)
+ if filter_re and not filter_re.search(stats.name):
+ continue
+ if table_fmt:
+ print(stats.table_row_str())
+ else:
+ print(stats.dict(now))
+
+ if interval == 0:
+ break
+ time.sleep(interval)
+
+if __name__ == "__main__":
+ main()
--
2.40.1
struct worker was laid out with the intent that all fields that are modified
for each work item execution are in the first cacheline. However, this
hasn't been true for a while with the addition of ->last_func. Let's just
collect hot fields together at the top.
Move ->sleeping in the hole after ->current_color and move ->lst_func right
below. While at it, drop the cacheline comment which isn't useful anymore.
Signed-off-by: Tejun Heo <[email protected]>
Cc: Lai Jiangshan <[email protected]>
---
kernel/workqueue_internal.h | 11 +++++------
1 file changed, 5 insertions(+), 6 deletions(-)
diff --git a/kernel/workqueue_internal.h b/kernel/workqueue_internal.h
index e00b1204a8e9..0600f04ceeb2 100644
--- a/kernel/workqueue_internal.h
+++ b/kernel/workqueue_internal.h
@@ -32,9 +32,12 @@ struct worker {
work_func_t current_func; /* L: current_work's fn */
struct pool_workqueue *current_pwq; /* L: current_work's pwq */
unsigned int current_color; /* L: current_work's color */
- struct list_head scheduled; /* L: scheduled works */
+ int sleeping; /* None */
+
+ /* used by the scheduler to determine a worker's last known identity */
+ work_func_t last_func; /* L: last work's fn */
- /* 64 bytes boundary on 64bit, 32 on 32bit */
+ struct list_head scheduled; /* L: scheduled works */
struct task_struct *task; /* I: worker task */
struct worker_pool *pool; /* A: the associated pool */
@@ -45,7 +48,6 @@ struct worker {
unsigned long last_active; /* L: last active timestamp */
unsigned int flags; /* X: flags */
int id; /* I: worker id */
- int sleeping; /* None */
/*
* Opaque string set with work_set_desc(). Printed out with task
@@ -55,9 +57,6 @@ struct worker {
/* used only by rescuers to point to the target workqueue */
struct workqueue_struct *rescue_wq; /* I: the workqueue to rescue */
-
- /* used by the scheduler to determine a worker's last known identity */
- work_func_t last_func;
};
/**
--
2.40.1
Workqueue now automatically marks per-cpu work items that hog CPU for too
long as CPU_INTENSIVE, which excludes them from concurrency management and
prevents stalling other concurrency-managed work items. If a work function
keeps running over the thershold, it likely needs to be switched to use an
unbound workqueue.
This patch adds a debug mechanism which tracks the work functions which
trigger the automatic CPU_INTENSIVE mechanism and report them using
pr_warn() with exponential backoff.
v3: Documentation update.
v2: Drop bouncing to kthread_worker for printing messages. It was to avoid
introducing circular locking dependency through printk but not effective
as it still had pool lock -> wci_lock -> printk -> pool lock loop. Let's
just print directly using printk_deferred().
Signed-off-by: Tejun Heo <[email protected]>
Suggested-by: Peter Zijlstra <[email protected]>
---
.../admin-guide/kernel-parameters.txt | 5 +
kernel/workqueue.c | 93 +++++++++++++++++++
lib/Kconfig.debug | 13 +++
3 files changed, 111 insertions(+)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 1f2185cf2f0a..3ed7dda4c994 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -6938,6 +6938,11 @@
them from noticeably delaying other per-cpu work
items. Default is 10000 (10ms).
+ If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel
+ will report the work functions which violate this
+ 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
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 3dc83d5eba50..4ca66384d288 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -948,6 +948,98 @@ static inline void worker_clr_flags(struct worker *worker, unsigned int flags)
pool->nr_running++;
}
+#ifdef CONFIG_WQ_CPU_INTENSIVE_REPORT
+
+/*
+ * Concurrency-managed per-cpu work items that hog CPU for longer than
+ * wq_cpu_intensive_thresh_us trigger the automatic CPU_INTENSIVE mechanism,
+ * which prevents them from stalling other concurrency-managed work items. If a
+ * work function keeps triggering this mechanism, it's likely that the work item
+ * should be using an unbound workqueue instead.
+ *
+ * wq_cpu_intensive_report() tracks work functions which trigger such conditions
+ * and report them so that they can be examined and converted to use unbound
+ * workqueues as appropriate. To avoid flooding the console, each violating work
+ * function is tracked and reported with exponential backoff.
+ */
+#define WCI_MAX_ENTS 128
+
+struct wci_ent {
+ work_func_t func;
+ atomic64_t cnt;
+ struct hlist_node hash_node;
+};
+
+static struct wci_ent wci_ents[WCI_MAX_ENTS];
+static int wci_nr_ents;
+static DEFINE_RAW_SPINLOCK(wci_lock);
+static DEFINE_HASHTABLE(wci_hash, ilog2(WCI_MAX_ENTS));
+
+static struct wci_ent *wci_find_ent(work_func_t func)
+{
+ struct wci_ent *ent;
+
+ hash_for_each_possible_rcu(wci_hash, ent, hash_node,
+ (unsigned long)func) {
+ if (ent->func == func)
+ return ent;
+ }
+ return NULL;
+}
+
+static void wq_cpu_intensive_report(work_func_t func)
+{
+ struct wci_ent *ent;
+
+restart:
+ ent = wci_find_ent(func);
+ if (ent) {
+ u64 cnt;
+
+ /*
+ * Start reporting from the fourth time and back off
+ * exponentially.
+ */
+ cnt = atomic64_inc_return_relaxed(&ent->cnt);
+ if (cnt >= 4 && is_power_of_2(cnt))
+ printk_deferred(KERN_WARNING "workqueue: %ps hogged CPU for >%luus %llu times, consider switching to WQ_UNBOUND\n",
+ ent->func, wq_cpu_intensive_thresh_us,
+ atomic64_read(&ent->cnt));
+ return;
+ }
+
+ /*
+ * @func is a new violation. Allocate a new entry for it. If wcn_ents[]
+ * is exhausted, something went really wrong and we probably made enough
+ * noise already.
+ */
+ if (wci_nr_ents >= WCI_MAX_ENTS)
+ return;
+
+ raw_spin_lock(&wci_lock);
+
+ if (wci_nr_ents >= WCI_MAX_ENTS) {
+ raw_spin_unlock(&wci_lock);
+ return;
+ }
+
+ if (wci_find_ent(func)) {
+ raw_spin_unlock(&wci_lock);
+ goto restart;
+ }
+
+ ent = &wci_ents[wci_nr_ents++];
+ ent->func = func;
+ atomic64_set(&ent->cnt, 1);
+ hash_add_rcu(wci_hash, &ent->hash_node, (unsigned long)func);
+
+ raw_spin_unlock(&wci_lock);
+}
+
+#else /* CONFIG_WQ_CPU_INTENSIVE_REPORT */
+static void wq_cpu_intensive_report(work_func_t func) {}
+#endif /* CONFIG_WQ_CPU_INTENSIVE_REPORT */
+
/**
* wq_worker_running - a worker is running again
* @task: task waking up
@@ -1057,6 +1149,7 @@ void wq_worker_tick(struct task_struct *task)
raw_spin_lock(&pool->lock);
worker_set_flags(worker, WORKER_CPU_INTENSIVE);
+ wq_cpu_intensive_report(worker->current_func);
pwq->stats[PWQ_STAT_CPU_INTENSIVE]++;
if (need_more_worker(pool)) {
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index ce51d4dc6803..97e880aa48d7 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1134,6 +1134,19 @@ config WQ_WATCHDOG
state. This can be configured through kernel parameter
"workqueue.watchdog_thresh" and its sysfs counterpart.
+config WQ_CPU_INTENSIVE_REPORT
+ bool "Report per-cpu work items which hog CPU for too long"
+ depends on DEBUG_KERNEL
+ help
+ Say Y here to enable reporting of concurrency-managed per-cpu work
+ items that hog CPUs for longer than
+ workqueue.cpu_intensive_threshold_us. Workqueue automatically
+ detects and excludes them from concurrency management to prevent
+ them from stalling other per-cpu work items. Occassional
+ triggering may not necessarily indicate a problem. Repeated
+ triggering likely indicates that the work item should be switched
+ to use an unbound workqueue.
+
config TEST_LOCKUP
tristate "Test module to generate lockups"
depends on m
--
2.40.1
Now that wq_worker_tick() is there, we can easily track the rough CPU time
consumption of each workqueue by charging the whole tick whenever a tick
hits an active workqueue. While not super accurate, it provides reasonable
visibility into the workqueues that consume a lot of CPU cycles.
wq_monitor.py is updated to report the per-workqueue CPU times.
v2: wq_monitor.py was using "cputime" as the key when outputting in json
format. Use "cpu_time" instead for consistency with other fields.
Signed-off-by: Tejun Heo <[email protected]>
---
Documentation/core-api/workqueue.rst | 38 ++++++++++++++--------------
kernel/workqueue.c | 3 +++
tools/workqueue/wq_monitor.py | 9 ++++++-
3 files changed, 30 insertions(+), 20 deletions(-)
diff --git a/Documentation/core-api/workqueue.rst b/Documentation/core-api/workqueue.rst
index a389f31b025c..a4c9b9d1905f 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 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 - -
+ total infl CPUtime CPUhog CMwake 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_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
+ 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_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 - -
+ sock_diag_events 0 0 0.0 0 0 - -
...
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 4ca66384d288..ee16ddb0647c 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -212,6 +212,7 @@ struct worker_pool {
enum pool_workqueue_stats {
PWQ_STAT_STARTED, /* work items started execution */
PWQ_STAT_COMPLETED, /* work items completed execution */
+ PWQ_STAT_CPU_TIME, /* total CPU time consumed */
PWQ_STAT_CPU_INTENSIVE, /* wq_cpu_intensive_thresh_us violations */
PWQ_STAT_CM_WAKEUP, /* concurrency-management worker wakeups */
PWQ_STAT_MAYDAY, /* maydays to rescuer */
@@ -1136,6 +1137,8 @@ void wq_worker_tick(struct task_struct *task)
if (!pwq)
return;
+ pwq->stats[PWQ_STAT_CPU_TIME] += TICK_USEC;
+
/*
* If the current worker is concurrency managed and hogged the CPU for
* longer than wq_cpu_intensive_thresh_us, it's automatically marked
diff --git a/tools/workqueue/wq_monitor.py b/tools/workqueue/wq_monitor.py
index 7c6f523b9164..6e258d123e8c 100644
--- a/tools/workqueue/wq_monitor.py
+++ b/tools/workqueue/wq_monitor.py
@@ -11,6 +11,10 @@ https://github.com/osandov/drgn.
infl The number of currently in-flight work items.
+ CPUtime Total CPU time consumed by the workqueue in seconds. This is
+ sampled from scheduler ticks and only provides ballpark
+ measurement. "nohz_full=" CPUs are excluded from measurement.
+
CPUitsv The number of times a concurrency-managed work item hogged CPU
longer than the threshold (workqueue.cpu_intensive_thresh_us)
and got excluded from concurrency management to avoid stalling
@@ -58,6 +62,7 @@ WQ_MEM_RECLAIM = prog['WQ_MEM_RECLAIM']
PWQ_STAT_STARTED = prog['PWQ_STAT_STARTED'] # work items started execution
PWQ_STAT_COMPLETED = prog['PWQ_STAT_COMPLETED'] # work items completed execution
+PWQ_STAT_CPU_TIME = prog['PWQ_STAT_CPU_TIME'] # total CPU time consumed
PWQ_STAT_CPU_INTENSIVE = prog['PWQ_STAT_CPU_INTENSIVE'] # wq_cpu_intensive_thresh_us violations
PWQ_STAT_CM_WAKEUP = prog['PWQ_STAT_CM_WAKEUP'] # concurrency-management worker wakeups
PWQ_STAT_MAYDAY = prog['PWQ_STAT_MAYDAY'] # maydays to rescuer
@@ -81,13 +86,14 @@ PWQ_NR_STATS = prog['PWQ_NR_STATS']
'mem_reclaim' : self.mem_reclaim,
'started' : self.stats[PWQ_STAT_STARTED],
'completed' : self.stats[PWQ_STAT_COMPLETED],
+ 'cpu_time' : self.stats[PWQ_STAT_CPU_TIME],
'cpu_intensive' : self.stats[PWQ_STAT_CPU_INTENSIVE],
'cm_wakeup' : self.stats[PWQ_STAT_CM_WAKEUP],
'mayday' : self.stats[PWQ_STAT_MAYDAY],
'rescued' : self.stats[PWQ_STAT_RESCUED], }
def table_header_str():
- return f'{"":>24} {"total":>8} {"infl":>5} '\
+ return f'{"":>24} {"total":>8} {"infl":>5} {"CPUtime":>8} '\
f'{"CPUitsv":>7} {"CMwake":>7} {"mayday":>7} {"rescued":>7}'
def table_row_str(self):
@@ -107,6 +113,7 @@ PWQ_NR_STATS = prog['PWQ_NR_STATS']
out = f'{self.name[-24:]:24} ' \
f'{self.stats[PWQ_STAT_STARTED]:8} ' \
f'{max(self.stats[PWQ_STAT_STARTED] - self.stats[PWQ_STAT_COMPLETED], 0):5} ' \
+ f'{self.stats[PWQ_STAT_CPU_TIME] / 1000000:8.1f} ' \
f'{cpu_intensive:>7} ' \
f'{cm_wakeup:>7} ' \
f'{mayday:>7} ' \
--
2.40.1
Applied to wq/for-6.5 w/ version tags in patch descriptions dropped.
Thanks.
--
tejun
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 <[email protected]>
Acked-by: Peter Zijlstra <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Lai Jiangshan <[email protected]>
---
.../admin-guide/kernel-parameters.txt | 7 ++
Documentation/core-api/workqueue.rst | 38 +++++------
kernel/sched/core.c | 3 +
kernel/workqueue.c | 68 +++++++++++++++++--
kernel/workqueue_internal.h | 2 +
tools/workqueue/wq_monitor.py | 13 +++-
6 files changed, 106 insertions(+), 25 deletions(-)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 9e5bab29685f..1f2185cf2f0a 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -6931,6 +6931,13 @@
it can be updated at runtime by writing to the
corresponding sysfs file.
+ workqueue.cpu_intensive_thresh_us=
+ Per-cpu work items which run for longer than this
+ threshold are automatically considered CPU intensive
+ and excluded from concurrency management to prevent
+ them from noticeably delaying other per-cpu work
+ items. Default is 10000 (10ms).
+
workqueue.disable_numa
By default, all work items queued to unbound
workqueues are affine to the NUMA nodes they're
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 - -
...
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 944c3ae39861..3484cada9a4a 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5632,6 +5632,9 @@ void scheduler_tick(void)
perf_event_task_tick();
+ if (curr->flags & PF_WQ_WORKER)
+ wq_worker_tick(curr);
+
#ifdef CONFIG_SMP
rq->idle_balance = idle_cpu(cpu);
trigger_load_balance(rq);
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 942421443603..3dc83d5eba50 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -212,6 +212,7 @@ struct worker_pool {
enum pool_workqueue_stats {
PWQ_STAT_STARTED, /* work items started execution */
PWQ_STAT_COMPLETED, /* work items completed execution */
+ PWQ_STAT_CPU_INTENSIVE, /* wq_cpu_intensive_thresh_us violations */
PWQ_STAT_CM_WAKEUP, /* concurrency-management worker wakeups */
PWQ_STAT_MAYDAY, /* maydays to rescuer */
PWQ_STAT_RESCUED, /* linked work items executed by rescuer */
@@ -332,6 +333,14 @@ static struct kmem_cache *pwq_cache;
static cpumask_var_t *wq_numa_possible_cpumask;
/* possible CPUs of each node */
+/*
+ * Per-cpu work items which run for longer than the following threshold are
+ * automatically considered CPU intensive and excluded from concurrency
+ * management to prevent them from noticeably delaying other per-cpu work items.
+ */
+static unsigned long wq_cpu_intensive_thresh_us = 10000;
+module_param_named(cpu_intensive_thresh_us, wq_cpu_intensive_thresh_us, ulong, 0644);
+
static bool wq_disable_numa;
module_param_named(disable_numa, wq_disable_numa, bool, 0444);
@@ -962,6 +971,13 @@ void wq_worker_running(struct task_struct *task)
if (!(worker->flags & WORKER_NOT_RUNNING))
worker->pool->nr_running++;
preempt_enable();
+
+ /*
+ * CPU intensive auto-detection cares about how long a work item hogged
+ * CPU without sleeping. Reset the starting timestamp on wakeup.
+ */
+ worker->current_at = worker->task->se.sum_exec_runtime;
+
worker->sleeping = 0;
}
@@ -1012,6 +1028,45 @@ void wq_worker_sleeping(struct task_struct *task)
raw_spin_unlock_irq(&pool->lock);
}
+/**
+ * wq_worker_tick - a scheduler tick occurred while a kworker is running
+ * @task: task currently running
+ *
+ * Called from scheduler_tick(). We're in the IRQ context and the current
+ * worker's fields which follow the 'K' locking rule can be accessed safely.
+ */
+void wq_worker_tick(struct task_struct *task)
+{
+ struct worker *worker = kthread_data(task);
+ struct pool_workqueue *pwq = worker->current_pwq;
+ struct worker_pool *pool = worker->pool;
+
+ if (!pwq)
+ return;
+
+ /*
+ * If the current worker is concurrency managed and hogged the CPU for
+ * longer than wq_cpu_intensive_thresh_us, it's automatically marked
+ * CPU_INTENSIVE to avoid stalling other concurrency-managed work items.
+ */
+ if ((worker->flags & WORKER_NOT_RUNNING) ||
+ worker->task->se.sum_exec_runtime - worker->current_at <
+ wq_cpu_intensive_thresh_us * NSEC_PER_USEC)
+ return;
+
+ raw_spin_lock(&pool->lock);
+
+ worker_set_flags(worker, WORKER_CPU_INTENSIVE);
+ pwq->stats[PWQ_STAT_CPU_INTENSIVE]++;
+
+ if (need_more_worker(pool)) {
+ pwq->stats[PWQ_STAT_CM_WAKEUP]++;
+ wake_up_worker(pool);
+ }
+
+ raw_spin_unlock(&pool->lock);
+}
+
/**
* wq_worker_last_func - retrieve worker's last work function
* @task: Task to retrieve last work function of.
@@ -2327,7 +2382,6 @@ __acquires(&pool->lock)
{
struct pool_workqueue *pwq = get_work_pwq(work);
struct worker_pool *pool = worker->pool;
- bool cpu_intensive = pwq->wq->flags & WQ_CPU_INTENSIVE;
unsigned long work_data;
struct worker *collision;
#ifdef CONFIG_LOCKDEP
@@ -2364,6 +2418,7 @@ __acquires(&pool->lock)
worker->current_work = work;
worker->current_func = work->func;
worker->current_pwq = pwq;
+ worker->current_at = worker->task->se.sum_exec_runtime;
work_data = *work_data_bits(work);
worker->current_color = get_work_color(work_data);
@@ -2381,7 +2436,7 @@ __acquires(&pool->lock)
* of concurrency management and the next code block will chain
* execution of the pending work items.
*/
- if (unlikely(cpu_intensive))
+ if (unlikely(pwq->wq->flags & WQ_CPU_INTENSIVE))
worker_set_flags(worker, WORKER_CPU_INTENSIVE);
/*
@@ -2461,9 +2516,12 @@ __acquires(&pool->lock)
raw_spin_lock_irq(&pool->lock);
- /* clear cpu intensive status */
- if (unlikely(cpu_intensive))
- worker_clr_flags(worker, WORKER_CPU_INTENSIVE);
+ /*
+ * In addition to %WQ_CPU_INTENSIVE, @worker may also have been marked
+ * CPU intensive by wq_worker_tick() if @work hogged CPU longer than
+ * wq_cpu_intensive_thresh_us. Clear it.
+ */
+ worker_clr_flags(worker, WORKER_CPU_INTENSIVE);
/* tag the worker for identification in schedule() */
worker->last_func = worker->current_func;
diff --git a/kernel/workqueue_internal.h b/kernel/workqueue_internal.h
index c2455be7b4c2..6b1d66e28269 100644
--- a/kernel/workqueue_internal.h
+++ b/kernel/workqueue_internal.h
@@ -31,6 +31,7 @@ struct worker {
struct work_struct *current_work; /* K: work being processed and its */
work_func_t current_func; /* K: function */
struct pool_workqueue *current_pwq; /* K: pwq */
+ u64 current_at; /* K: runtime at start or last wakeup */
unsigned int current_color; /* K: color */
int sleeping; /* S: is worker sleeping? */
@@ -76,6 +77,7 @@ static inline struct worker *current_wq_worker(void)
*/
void wq_worker_running(struct task_struct *task);
void wq_worker_sleeping(struct task_struct *task);
+void wq_worker_tick(struct task_struct *task);
work_func_t wq_worker_last_func(struct task_struct *task);
#endif /* _KERNEL_WORKQUEUE_INTERNAL_H */
diff --git a/tools/workqueue/wq_monitor.py b/tools/workqueue/wq_monitor.py
index fc1643ba06b3..7c6f523b9164 100644
--- a/tools/workqueue/wq_monitor.py
+++ b/tools/workqueue/wq_monitor.py
@@ -11,6 +11,11 @@ https://github.com/osandov/drgn.
infl The number of currently in-flight work items.
+ CPUitsv The number of times a concurrency-managed work item hogged CPU
+ longer than the threshold (workqueue.cpu_intensive_thresh_us)
+ and got excluded from concurrency management to avoid stalling
+ other work items.
+
CMwake The number of concurrency-management wake-ups while executing a
work item of the workqueue.
@@ -53,6 +58,7 @@ WQ_MEM_RECLAIM = prog['WQ_MEM_RECLAIM']
PWQ_STAT_STARTED = prog['PWQ_STAT_STARTED'] # work items started execution
PWQ_STAT_COMPLETED = prog['PWQ_STAT_COMPLETED'] # work items completed execution
+PWQ_STAT_CPU_INTENSIVE = prog['PWQ_STAT_CPU_INTENSIVE'] # wq_cpu_intensive_thresh_us violations
PWQ_STAT_CM_WAKEUP = prog['PWQ_STAT_CM_WAKEUP'] # concurrency-management worker wakeups
PWQ_STAT_MAYDAY = prog['PWQ_STAT_MAYDAY'] # maydays to rescuer
PWQ_STAT_RESCUED = prog['PWQ_STAT_RESCUED'] # linked work items executed by rescuer
@@ -75,19 +81,23 @@ PWQ_NR_STATS = prog['PWQ_NR_STATS']
'mem_reclaim' : self.mem_reclaim,
'started' : self.stats[PWQ_STAT_STARTED],
'completed' : self.stats[PWQ_STAT_COMPLETED],
+ 'cpu_intensive' : self.stats[PWQ_STAT_CPU_INTENSIVE],
'cm_wakeup' : self.stats[PWQ_STAT_CM_WAKEUP],
'mayday' : self.stats[PWQ_STAT_MAYDAY],
'rescued' : self.stats[PWQ_STAT_RESCUED], }
def table_header_str():
- return f'{"":>24} {"total":>8} {"infl":>5} {"CMwake":>7} {"mayday":>7} {"rescued":>7}'
+ return f'{"":>24} {"total":>8} {"infl":>5} '\
+ f'{"CPUitsv":>7} {"CMwake":>7} {"mayday":>7} {"rescued":>7}'
def table_row_str(self):
+ cpu_intensive = '-'
cm_wakeup = '-'
mayday = '-'
rescued = '-'
if not self.unbound:
+ cpu_intensive = str(self.stats[PWQ_STAT_CPU_INTENSIVE])
cm_wakeup = str(self.stats[PWQ_STAT_CM_WAKEUP])
if self.mem_reclaim:
@@ -97,6 +107,7 @@ PWQ_NR_STATS = prog['PWQ_NR_STATS']
out = f'{self.name[-24:]:24} ' \
f'{self.stats[PWQ_STAT_STARTED]:8} ' \
f'{max(self.stats[PWQ_STAT_STARTED] - self.stats[PWQ_STAT_COMPLETED], 0):5} ' \
+ f'{cpu_intensive:>7} ' \
f'{cm_wakeup:>7} ' \
f'{mayday:>7} ' \
f'{rescued:>7} '
--
2.40.1