Re: [PATCH 2/3] workqueue: expose per-workqueue stats in debugfs

[Tejun Heo]

Hello, Wilson.

On Thu, Oct 22, 2026 at 10:46:19PM +0000, Wilson Felipe Pereira wrote:
> Why not drgn? For continuous monitoring, running drgn on every machine,
> with vmlinux debuginfo, and memory footprint from Python/drgn, while
> having CONFIG_PROC_KCORE available, it adds up. Having a simple file
> interface, it can be read from an existing monitoring collector.
>
> Why debugfs? If sysfs is picked, not all queues are in
> /sys/bus/workqueue/devices/. Using debugfs, a single file can include
> all queues. If you have a suggestion, I'm open to change this series.

I'm usually really skeptical when people suggest debugfs as a solution.
If you need continuous monitoring and drgn is too heavy, this is trivial
to do with BPF. The following bpftrace script prints the per-workqueue
stats and needs only BTF, no DWARF debuginfo, /proc/kcore or Python:

  BEGIN
  {
      printf("%-24s %10s %10s %12s %6s %6s %6s\n", "workqueue", "started",
             "completed", "cpu_time_us", "active", "cmw", "mayday");

      $whead = (uint64)kaddr("workqueues");
      $wpos = (uint64)((struct list_head *)$whead)->next;
      for ($i : 0..4096) {
          if ($wpos == $whead) {
              break;
          }
          $wq = (struct workqueue_struct *)($wpos - offsetof(struct workqueue_struct, list));
          $started = (uint64)0; $completed = (uint64)0; $cpu = (uint64)0;
          $cmw = (uint64)0; $mayday = (uint64)0; $active = 0;

          $phead = (uint64)$wq + offsetof(struct workqueue_struct, pwqs);
          $ppos = (uint64)((struct list_head *)$phead)->next;
          for ($j : 0..8192) {
              if ($ppos == $phead) {
                  break;
              }
              $pwq = (struct pool_workqueue *)($ppos - offsetof(struct pool_workqueue, pwqs_node));
              $started += $pwq->stats[PWQ_STAT_STARTED];
              $completed += $pwq->stats[PWQ_STAT_COMPLETED];
              $cpu += $pwq->stats[PWQ_STAT_CPU_TIME];
              $cmw += $pwq->stats[PWQ_STAT_CM_WAKEUP];
              $mayday += $pwq->stats[PWQ_STAT_MAYDAY];
              $active += $pwq->nr_active;
              $ppos = (uint64)((struct list_head *)$ppos)->next;
          }

          printf("%-24s %10lu %10lu %12lu %6d %6lu %6lu\n", $wq->name, $started,
                 $completed, $cpu, $active, $cmw, $mayday);
          $wpos = (uint64)((struct list_head *)$wpos)->next;
      }
      exit();
  }

It took an AI agent about a minute to write and test.

Thanks.

--
tejun