Re: [PATCH 2/2][RESEND v3] PM-runtime: change the tracepoints to cover all usage_count

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

On Wed, Jul 15, 2020 at 02:28:03PM +0800, Chen Yu wrote:
> Commit d229290689ae ("PM-runtime: add tracepoints for usage_count changes")
> has added some tracepoints to monitor the change of runtime usage, and
> there is something to improve:
> 1. There are some places that adjust the usage count not
>    been traced yet. For example, pm_runtime_get_noresume() and
>    pm_runtime_put_noidle()
> 2. The change of the usage count will not be tracked if decreased
>    from 1 to 0.
> 
> This patch intends to adjust the logic to be consistent with the
> change of usage_counter, that is to say, only after the counter has
> been possibly modified, we record it. Besides, all usage changes will
> be shown using rpm_usage even if included by other trace points.
> And these changes has helped track down the e1000e runtime issue.
> 
> Reviewed-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
> Signed-off-by: Chen Yu <yu.c.chen@intel.com>
> ---
>  drivers/base/power/runtime.c | 38 +++++++++++++++++++++++-------------
>  1 file changed, 24 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c
> index 85a248e196ca..5789d2624513 100644
> --- a/drivers/base/power/runtime.c
> +++ b/drivers/base/power/runtime.c
> @@ -1004,10 +1004,11 @@ 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)) {
> -			trace_rpm_usage_rcuidle(dev, rpmflags);
> +		bool non_zero = !atomic_dec_and_test(&dev->power.usage_count);
> +
> +		trace_rpm_usage_rcuidle(dev, rpmflags);

Why not just call trace everywhere before you do the atomic operations?
Why does the trace need to be called after the operation everywhere?

thanks,

greg k-h