linux-kernel - Re: [PATCH 2/2][RFC] PM-runtime: add tracepoints to cover all usage

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Date:   Fri, 5 Jun 2020 21:33:11 +0200
From:   Michal Miroslaw <mirq-linux@...e.qmqm.pl>
To:     Chen Yu <yu.c.chen@...el.com>
Cc:     "Rafael J . Wysocki" <rafael@...nel.org>,
        Len Brown <len.brown@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2][RFC] PM-runtime: add tracepoints to cover all
 usage_count changes

On Sat, Jun 06, 2020 at 03:05:52AM +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 have 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.
[...]
> @@ -1448,16 +1453,17 @@ EXPORT_SYMBOL_GPL(pm_runtime_forbid);
>   */
>  void pm_runtime_allow(struct device *dev)
>  {
> +	bool is_zero;
> +
>  	spin_lock_irq(&dev->power.lock);
>  	if (dev->power.runtime_auto)
>  		goto out;
>  
>  	dev->power.runtime_auto = true;
> -	if (atomic_dec_and_test(&dev->power.usage_count))
> +	is_zero = atomic_dec_and_test(&dev->power.usage_count);
> +	trace_rpm_usage_rcuidle(dev, RPM_AUTO | RPM_ASYNC);
> +	if (is_zero)
>  		rpm_idle(dev, RPM_AUTO | RPM_ASYNC);
> -	else
> -		trace_rpm_usage_rcuidle(dev, RPM_AUTO | RPM_ASYNC);
> -
[...]

IIRC, rpm_idle() has a tracepoint already.

> @@ -1523,9 +1529,8 @@ static void update_autosuspend(struct device *dev, int old_delay, int old_use)
>  		/* If it used to be allowed then prevent it. */
>  		if (!old_use || old_delay >= 0) {
>  			atomic_inc(&dev->power.usage_count);
> -			rpm_resume(dev, 0);
> -		} else {
>  			trace_rpm_usage_rcuidle(dev, 0);
> +			rpm_resume(dev, 0);
>  		}
>  	}
[...]

This actually changes logic, so it doesn't match the patch description.

Best Regards
Michał Mirosław