Re: [PATCH][experimantal] cpufreq: governor: Use an atomic variable for synchronization

Viresh Kumar
2015-12-08T16:34:07Z

On 08-12-15, 17:42, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> Subject: [PATCH] cpufreq: governor: Use lockless timer function
>
> It is possible to get rid of the timer_lock spinlock used by the
> governor timer function for synchronization, but a couple of races
> need to be avoided.
>
> The first race is between multiple dbs_timer_handler() instances
> that may be running in parallel with each other on different
> CPUs. Namely, one of them has to queue up the work item, but it
> cannot be queued up more than once. To achieve that,
> atomic_inc_return() can be used on the skip_work field of
> struct cpu_common_dbs_info.
>
> The second race is between an already running dbs_timer_handler()
> and gov_cancel_work(). In that case the dbs_timer_handler() might
> not notice the skip_work incrementation in gov_cancel_work() and
> it might queue up its work item after gov_cancel_work() had
> returned (and that work item would corrupt skip_work going
> forward). To prevent that from happening, gov_cancel_work()
> can be made wait for the timer function to complete (on all CPUs)
> right after skip_work has been incremented.
>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> ---
> drivers/cpufreq/cpufreq_governor.c | 49 ++++++++++++++++---------------------
> drivers/cpufreq/cpufreq_governor.h | 9 +-----
> 2 files changed, 24 insertions(+), 34 deletions(-)

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

--
viresh