Re: [PATCH 06/10] cpufreq: ondemand: Drop unnecessary locks from update_sampling_rate()

[Preeti U Murthy <preeti@linux.vnet.ibm.com>]

On 06/22/2015 01:32 PM, Viresh Kumar wrote:
> 'timer_mutex' is required to sync work-handlers of policy->cpus.
> update_sampling_rate() is just canceling the works and queuing them
> again. This isn't protecting anything at all in update_sampling_rate()
> and is not gonna be of any use.
> 
> Even if a work-handler is already running for a CPU,
> cancel_delayed_work_sync() will wait for it to finish.
> 
> Drop these unnecessary locks.
> 
> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

Reviewed-by: Preeti U Murthy <preeti@linux.vnet.ibm.com>
> ---
>  drivers/cpufreq/cpufreq_ondemand.c | 10 +---------
>  1 file changed, 1 insertion(+), 9 deletions(-)
> 
> diff --git a/drivers/cpufreq/cpufreq_ondemand.c b/drivers/cpufreq/cpufreq_ondemand.c
> index 774bbddae2c9..841e1fa96ee7 100644
> --- a/drivers/cpufreq/cpufreq_ondemand.c
> +++ b/drivers/cpufreq/cpufreq_ondemand.c
> @@ -267,28 +267,20 @@ static void update_sampling_rate(struct dbs_data *dbs_data,
>  		dbs_info = &per_cpu(od_cpu_dbs_info, cpu);
>  		cpufreq_cpu_put(policy);
> 
> -		mutex_lock(&dbs_info->cdbs.ccdbs->timer_mutex);
> -
> -		if (!delayed_work_pending(&dbs_info->cdbs.dwork)) {
> -			mutex_unlock(&dbs_info->cdbs.ccdbs->timer_mutex);
> +		if (!delayed_work_pending(&dbs_info->cdbs.dwork))
>  			continue;
> -		}
> 
>  		next_sampling = jiffies + usecs_to_jiffies(new_rate);
>  		appointed_at = dbs_info->cdbs.dwork.timer.expires;
> 
>  		if (time_before(next_sampling, appointed_at)) {
> -
> -			mutex_unlock(&dbs_info->cdbs.ccdbs->timer_mutex);
>  			cancel_delayed_work_sync(&dbs_info->cdbs.dwork);
> -			mutex_lock(&dbs_info->cdbs.ccdbs->timer_mutex);
> 
>  			gov_queue_work(dbs_data, policy,
>  				       usecs_to_jiffies(new_rate),
>  				       cpumask_of(cpu));
> 
>  		}
> -		mutex_unlock(&dbs_info->cdbs.ccdbs->timer_mutex);
>  	}
>  }
>