Re: [PATCH] PM-runtime: add tracepoints for usage_count changes

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Sat, Jan 04, 2020 at 05:27:57PM +0100, Michał Mirosław wrote:
> Add tracepoints to remaining places where device's power.usage_count
> is changed. This helps debugging where and why autosuspend is prevented.
> 
> Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
> ---
>  drivers/base/power/runtime.c | 13 +++++++++++--
>  include/trace/events/rpm.h   |  6 ++++++
>  2 files changed, 17 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c
> index 48616f358854..16134a69bf6f 100644
> --- a/drivers/base/power/runtime.c
> +++ b/drivers/base/power/runtime.c
> @@ -1006,8 +1006,10 @@ int __pm_runtime_idle(struct device *dev, int rpmflags)
>  	int retval;
>  
>  	if (rpmflags & RPM_GET_PUT) {
> -		if (!atomic_dec_and_test(&dev->power.usage_count))
> +		if (!atomic_dec_and_test(&dev->power.usage_count)) {
> +			trace_rpm_usage_rcuidle(dev, rpmflags);

Who and what is really going to use these tracepoints?

And putting them in these if statements seems odd, are you sure that's
the correct place?  What do these show to userspace?

>  			return 0;
> +		}
>  	}
>  
>  	might_sleep_if(!(rpmflags & RPM_ASYNC) && !dev->power.irq_safe);
> @@ -1038,8 +1040,10 @@ int __pm_runtime_suspend(struct device *dev, int rpmflags)
>  	int retval;
>  
>  	if (rpmflags & RPM_GET_PUT) {
> -		if (!atomic_dec_and_test(&dev->power.usage_count))
> +		if (!atomic_dec_and_test(&dev->power.usage_count)) {
> +			trace_rpm_usage_rcuidle(dev, rpmflags);
>  			return 0;
> +		}
>  	}
>  
>  	might_sleep_if(!(rpmflags & RPM_ASYNC) && !dev->power.irq_safe);
> @@ -1101,6 +1105,7 @@ int pm_runtime_get_if_in_use(struct device *dev)
>  	retval = dev->power.disable_depth > 0 ? -EINVAL :
>  		dev->power.runtime_status == RPM_ACTIVE
>  			&& atomic_inc_not_zero(&dev->power.usage_count);
> +	trace_rpm_usage_rcuidle(dev, 0);

Why this one?


>  	spin_unlock_irqrestore(&dev->power.lock, flags);
>  	return retval;
>  }
> @@ -1434,6 +1439,8 @@ void pm_runtime_allow(struct device *dev)
>  	dev->power.runtime_auto = true;
>  	if (atomic_dec_and_test(&dev->power.usage_count))
>  		rpm_idle(dev, RPM_AUTO | RPM_ASYNC);
> +	else
> +		trace_rpm_usage_rcuidle(dev, RPM_AUTO | RPM_ASYNC);

Are you sure this is correct?

These feel odd...

thanks,

greg k-h