Re: [PATCH] cpufreq: stats: Make the stats code non-modular

From: Viresh Kumar
Date: Mon May 30 2016 - 00:54:07 EST

On 28-05-16, 15:15, Rafael J. Wysocki wrote:
> It does, but there's a problem.
> If fast frequency switching is in use, the stats attributes just sit there
> full of zeros (because the stats are not updated then) which is confusing.
> Of course, the ultimate solution here would be to make the stats actually
> work with fast frequency switching, but that requires some major surgery of
> the stats code, so for now I'd like to simply make those attributes return
> nothing if fast frequency switching is enabled for the policy (returning
> -EBUSY from there, which would have been cleaner, unfortunately breaks
> powertop).

What's stopping us from doing that? Sorry I don't remember that well :(

I mean, why can't we call cpufreq_stats_record_transition() somehow via that
code ?

> Updated patch is below.
> ---
> From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> Subject: [PATCH] cpufreq: stats: Make the stats code non-modular
> The modularity of cpufreq_stats is quite problematic.
> First off, the usage of policy notifiers for the initialization
> and cleanup in the cpufreq_stats module is inherently racy with
> respect to CPU offline/online and the initialization and cleanup
> of the cpufreq driver.
> Second, fast frequency switching (used by the schedutil governor)
> cannot be enabled if any transition notifiers are registered, so
> if the cpufreq_stats module (that registers a transition notifier
> for updating transition statistics) is loaded, the schedutil governor
> cannot use fast frequency switching.
> On the other hand, allowing cpufreq_stats to be built as a module
> doesn't really add much value. Arguably, there's not much reason
> for that code to be modular at all.
> For the above reasons, make the cpufreq stats code non-modular,
> modify the core to invoke functions provided by that code directly
> and drop the notifiers from it.
> Make the stats sysfs attributes appear empty if fast frequency
> switching is enabled as the statistics will not be updated in that
> case anyway (and returning -EBUSY from those attributes breaks
> powertop).
> While at it, clean up Kconfig help for the CPU_FREQ_STAT and
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> ---
> drivers/cpufreq/Kconfig | 13 +--
> drivers/cpufreq/cpufreq.c | 4 +
> drivers/cpufreq/cpufreq_stats.c | 152 +++++-----------------------------------
> include/linux/cpufreq.h | 12 +++
> 4 files changed, 40 insertions(+), 141 deletions(-)

Acked-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>