Re: [PATCH 5.15 2/3] timers/nohz: Switch to ONESHOT_STOPPED in the low-res handler when the tick is stopped

On Sun, Aug 13, 2023 at 03:16:19AM +0000, Joel Fernandes (Google) wrote:

From: Nicholas Piggin npiggin@gmail.com

[ Upstream commit 5417ddc1cf1f5c8cba31ab217cf57ada7ab6ea88 ]

I have the wrong SHA here, it should be: 62c1256d544747b38e77ca9b5bfe3a26f9592576

If you don't mind correcting it, please go ahead. Or I can resend the patch in the future.

thanks,

- Joel

When tick_nohz_stop_tick() stops the tick and high resolution timers are disabled, then the clock event device is not put into ONESHOT_STOPPED mode. This can lead to spurious timer interrupts with some clock event device drivers that don't shut down entirely after firing.

Eliminate these by putting the device into ONESHOT_STOPPED mode at points where it is not being reprogrammed. When there are no timers active, then tick_program_event() with KTIME_MAX can be used to stop the device. When there is a timer active, the device can be stopped at the next tick (any new timer added by timers will reprogram the tick).

Signed-off-by: Nicholas Piggin npiggin@gmail.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Link: https://lore.kernel.org/r/20220422141446.915024-1-npiggin@gmail.com Signed-off-by: Joel Fernandes (Google) joel@joelfernandes.org

---

kernel/time/tick-sched.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index 7701c720dc1f..5786e2794ae1 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -950,6 +950,8 @@ static void tick_nohz_stop_tick(struct tick_sched *ts, int cpu) if (unlikely(expires == KTIME_MAX)) { if (ts->nohz_mode == NOHZ_MODE_HIGHRES) hrtimer_cancel(&ts->sched_timer);

• else
  

• 	tick_program_event(KTIME_MAX, 1);
  

  return; }

@@ -1356,9 +1358,15 @@ static void tick_nohz_handler(struct clock_event_device *dev) tick_sched_do_timer(ts, now); tick_sched_handle(ts, regs);

• /* No need to reprogram if we are running tickless */
• if (unlikely(ts->tick_stopped))

• if (unlikely(ts->tick_stopped)) {

• /*
  

•  * The clockevent device is not reprogrammed, so change the
  

•  * clock event device to ONESHOT_STOPPED to avoid spurious
  

•  * interrupts on devices which might not be truly one shot.
  

•  */
  

• tick_program_event(KTIME_MAX, 1);
  

  return;
• }

hrtimer_forward(&ts->sched_timer, now, TICK_NSEC); tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1); -- 2.41.0.640.ga95def55d0-goog