linux-kernel - Re: [PATCH] drivers: base: initcall_debug logs for driver probe times

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Date:   Wed, 20 Jun 2018 08:28:57 -0600
From:   Rob Herring <robh+dt@...nel.org>
To:     Todd Poynor <toddpoynor@...il.com>
Cc:     Frank Rowand <frowand.list@...il.com>, devicetree@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Android Kernel Team <kernel-team@...roid.com>,
        Todd Poynor <toddpoynor@...gle.com>
Subject: Re: [PATCH] drivers: base: initcall_debug logs for driver probe times

On Tue, Jun 19, 2018 at 8:39 PM, Todd Poynor <toddpoynor@...il.com> wrote:
> From: Todd Poynor <toddpoynor@...gle.com>
>
> Add initcall_debug logs for each driver device probe call, for example:
>
>    probe of a3800000.ramoops returned after 3007 usecs
>
> This replaces the previous code added to report times for deferred
> probes.  It also reports OF platform bus device creates that were
> formerly lumped together in a single entry for function
> of_platform_default_populate_init, as well as helping to annotate other
> initcalls that involve device probing.
>
> Signed-off-by: Todd Poynor <toddpoynor@...gle.com>
> ---
>  drivers/base/dd.c | 50 +++++++++++++++++++++++------------------------
>  1 file changed, 24 insertions(+), 26 deletions(-)
>
> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> index 1435d7281c66..56db446a467a 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -62,26 +62,6 @@ static bool initcalls_done;
>   */
>  static bool defer_all_probes;
>
> -/*
> - * For initcall_debug, show the deferred probes executed in late_initcall
> - * processing.
> - */
> -static void deferred_probe_debug(struct device *dev)
> -{
> -       ktime_t calltime, delta, rettime;
> -       unsigned long long duration;
> -
> -       printk(KERN_DEBUG "deferred probe %s @ %i\n", dev_name(dev),
> -              task_pid_nr(current));
> -       calltime = ktime_get();
> -       bus_probe_device(dev);
> -       rettime = ktime_get();
> -       delta = ktime_sub(rettime, calltime);
> -       duration = (unsigned long long) ktime_to_ns(delta) >> 10;
> -       printk(KERN_DEBUG "deferred probe %s returned after %lld usecs\n",
> -              dev_name(dev), duration);
> -}
> -
>  /*
>   * deferred_probe_work_func() - Retry probing devices in the active list.
>   */
> @@ -125,11 +105,7 @@ static void deferred_probe_work_func(struct work_struct *work)
>                 device_pm_move_to_tail(dev);
>
>                 dev_dbg(dev, "Retrying from deferred list\n");
> -               if (initcall_debug && !initcalls_done)
> -                       deferred_probe_debug(dev);
> -               else
> -                       bus_probe_device(dev);
> -
> +               bus_probe_device(dev);
>                 mutex_lock(&deferred_probe_mutex);
>
>                 put_device(dev);
> @@ -527,6 +503,25 @@ static int really_probe(struct device *dev, struct device_driver *drv)
>         return ret;
>  }
>
> +/*
> + * For initcall_debug, show the driver probe time.
> + */
> +static int really_probe_debug(struct device *dev, struct device_driver *drv)
> +{
> +       ktime_t calltime, delta, rettime;
> +       unsigned long long duration;

Probably should be s64.

> +       int ret;
> +
> +       calltime = ktime_get();
> +       ret = really_probe(dev, drv);
> +       rettime = ktime_get();
> +       delta = ktime_sub(rettime, calltime);
> +       duration = (unsigned long long) ktime_to_ns(delta) >> 10;

Is avoiding a divide really worth optimizing here compared to the
flood of messages typically on the serial port? Just use ktime_to_us.
Perhaps just get rid of duration and do the conversion in the printk
arg.

> +       printk(KERN_DEBUG "probe of %s returned after %lld usecs\n",
> +              dev_name(dev), duration);

Including the return code here too would be good.

> +       return ret;
> +}
> +
>  /**
>   * driver_probe_done
>   * Determine if the probe sequence is finished or not.
> @@ -585,7 +580,10 @@ int driver_probe_device(struct device_driver *drv, struct device *dev)
>                 pm_runtime_get_sync(dev->parent);
>
>         pm_runtime_barrier(dev);
> -       ret = really_probe(dev, drv);
> +       if (initcall_debug && !initcalls_done)
> +               ret = really_probe_debug(dev, drv);
> +       else
> +               ret = really_probe(dev, drv);
>         pm_request_idle(dev);
>
>         if (dev->parent)
> --
> 2.18.0.rc1.244.gcf134e6275-goog
>