| Message ID | 20210923153339.623208460@linutronix.de (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | hrtimers: Cleanup hrtimer_forward() [ab]use | expand |
On Thu, 23 Sep 2021 18:04:25 +0200, Thomas Gleixner wrote: > > The hrtimer callback pcsp_do_timer() prepares rearming of the timer with > hrtimer_forward(). hrtimer_forward() is intended to provide a mechanism to > forward the expiry time of the hrtimer by a multiple of the period argument > so that the expiry time greater than the time provided in the 'now' > argument. > > pcsp_do_timer() invokes hrtimer_forward() with the current timer expiry > time as 'now' argument. That's providing a periodic timer expiry, but is > not really robust when the timer callback is delayed so that the resulting > new expiry time is already in the past which causes the callback to be > invoked immediately again. If the timer is delayed then the back to back > invocation is not really making it better than skipping the missed > periods. Sound is distorted in any case. > > Use hrtimer_forward_now() which ensures that the next expiry is in the > future. This prevents hogging the CPU in the timer expiry code and allows > later on to remove hrtimer_forward() from the public interfaces. > > Signed-off-by: Thomas Gleixner <tglx@linutronix.de> > Cc: alsa-devel@alsa-project.org > Cc: Takashi Iwai <tiwai@suse.com> > Cc: Jaroslav Kysela <perex@perex.cz> Thanks, applied now to sound git tree. Takashi
--- a/sound/drivers/pcsp/pcsp_lib.c +++ b/sound/drivers/pcsp/pcsp_lib.c @@ -143,7 +143,7 @@ enum hrtimer_restart pcsp_do_timer(struc if (pointer_update) pcsp_pointer_update(chip); - hrtimer_forward(handle, hrtimer_get_expires(handle), ns_to_ktime(ns)); + hrtimer_forward_now(handle, ns_to_ktime(ns)); return HRTIMER_RESTART; }
The hrtimer callback pcsp_do_timer() prepares rearming of the timer with hrtimer_forward(). hrtimer_forward() is intended to provide a mechanism to forward the expiry time of the hrtimer by a multiple of the period argument so that the expiry time greater than the time provided in the 'now' argument. pcsp_do_timer() invokes hrtimer_forward() with the current timer expiry time as 'now' argument. That's providing a periodic timer expiry, but is not really robust when the timer callback is delayed so that the resulting new expiry time is already in the past which causes the callback to be invoked immediately again. If the timer is delayed then the back to back invocation is not really making it better than skipping the missed periods. Sound is distorted in any case. Use hrtimer_forward_now() which ensures that the next expiry is in the future. This prevents hogging the CPU in the timer expiry code and allows later on to remove hrtimer_forward() from the public interfaces. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: alsa-devel@alsa-project.org Cc: Takashi Iwai <tiwai@suse.com> Cc: Jaroslav Kysela <perex@perex.cz> --- sound/drivers/pcsp/pcsp_lib.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)