On Tue, Jul 11, 2023 at 3:55 PM Geert Uytterhoeven [off-list ref] wrote:

Hi Tejun,

On Fri, May 12, 2023 at 9:54 PM Tejun Heo [off-list ref] wrote:

quoted

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.

v2: Drop bouncing through kthread_worker for printing messages. It was to
    avoid introducing circular locking dependency but wasn't 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 <tj@kernel.org>
Suggested-by: Peter Zijlstra <peterz@infradead.org>

Thanks for your patch, which is now commit 6363845005202148
("workqueue: Report work funcs that trigger automatic CPU_INTENSIVE
mechanism") in v6.5-rc1.

I guess you are interested to know where this triggers.
I enabled CONFIG_WQ_CPU_INTENSIVE_REPORT=y, and tested
the result on various machines...

OrangeCrab/Linux-on-LiteX-VexRiscV with ht16k33 14-seg display and ssd130xdrmfb:

  workqueue: check_lifetime hogged CPU for >10000us 4 times, consider
switching to WQ_UNBOUND
  workqueue: drm_fb_helper_damage_work hogged CPU for >10000us 1024
times, consider switching to WQ_UNBOUND
  workqueue: fb_flashcursor hogged CPU for >10000us 128 times,
consider switching to WQ_UNBOUND
  workqueue: ht16k33_seg14_update hogged CPU for >10000us 128 times,
consider switching to WQ_UNBOUND
  workqueue: mmc_rescan hogged CPU for >10000us 128 times, consider
switching to WQ_UNBOUND

Got one more after a while:

workqueue: neigh_managed_work hogged CPU for >10000us 4 times,
consider switching to WQ_UNBOUND

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds