workqueue: Track and monitor per-workqueue CPU time usage

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 <tj@kernel.org>

diff --git a/Documentation/core-api/workqueue.rst b/Documentation/core-api/workqueue.rst
index a389f31..a4c9b9d 100644 (file)
--- 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 4ca6638..ee16ddb 100644 (file)
--- 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 7c6f523..6e258d1 100644 (file)
--- 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 @@ class WqStats:
                  '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 @@ class WqStats:
         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} ' \