Re: [PATCH][RFC v2] ACPI: acpi_pad: Do not launch acpi_pad threads on idle cpus

[joeyli <jlee@suse.com>]

Hi Chen Yu and ACPI experts,

On Sat, May 05, 2018 at 07:53:22PM +0800, Chen Yu wrote:
> According to current implementation of acpi_pad driver,
> it does not make sense to spawn any power saving threads
> on the cpus which are already idle - it might bring
> unnecessary overhead on these idle cpus and causes power
> waste. So verify the condition that if the number of 'busy'
> cpus exceeds the amount of the 'forced idle' cpus is met.
> This is applicable due to round-robin attribute of the
> power saving threads, otherwise ignore the setting/ACPI
> notification.
> 
> Suggested-by: Lenny Szubowicz <lszubowi@redhat.com>
> Suggested-by: Len Brown <lenb@kernel.org>
> Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
> Cc: Lenny Szubowicz <lszubowi@redhat.com>
> Cc: Len Brown <lenb@kernel.org>
> Cc: Jacob Pan <jacob.jun.pan@linux.intel.com>
> Cc: Rui Zhang <rui.zhang@intel.com>
> Cc: linux-acpi@vger.kernel.org
> Signed-off-by: Chen Yu <yu.c.chen@intel.com>

Do you have any news for this patch? Why it did not merged by kernel
maineline?

Thanks a lot!
Joey Lee

> ---
>  drivers/acpi/acpi_pad.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 51 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/acpi/acpi_pad.c b/drivers/acpi/acpi_pad.c
> index 552c1f7..515e60e 100644
> --- a/drivers/acpi/acpi_pad.c
> +++ b/drivers/acpi/acpi_pad.c
> @@ -254,12 +254,62 @@ static void set_power_saving_task_num(unsigned int num)
>  	}
>  }
>  
> +/*
> + * Extra acpi_pad threads should not be created until
> + * the requested idle count is less than/equals to the
> + * number of the busy cpus - it does not make sense to
> + * throttle the idle cpus.
> + */
> +#define SAMPLE_INTERVAL_JIF	20
> +
> +static u64 get_idle_time(int cpu)
> +{
> +	u64 idle, idle_usecs = -1ULL;
> +
> +	idle_usecs = get_cpu_idle_time_us(cpu, NULL);
> +
> +	if (idle_usecs == -1ULL)
> +		idle = kcpustat_cpu(cpu).cpustat[CPUTIME_IDLE];
> +	else
> +		idle = idle_usecs * NSEC_PER_USEC;
> +
> +	return idle;
> +}
> +
> +static bool idle_nr_valid(unsigned int num_cpus)
> +{
> +	int busy_nr = 0, i = 0, load_thresh = 100 - idle_pct;
> +
> +	if (!num_cpus)
> +		return true;
> +
> +	for_each_online_cpu(i) {
> +		u64 wall_time, idle_time;
> +		unsigned int elapsed_delta, idle_delta, load;
> +
> +		wall_time = jiffies64_to_nsecs(get_jiffies_64());
> +		idle_time = get_idle_time(i);
> +		/* Wait and see... */
> +		schedule_timeout_uninterruptible(SAMPLE_INTERVAL_JIF);
> +
> +		idle_delta = get_idle_time(i) - idle_time;
> +		elapsed_delta = jiffies64_to_nsecs(get_jiffies_64()) - wall_time;
> +		idle_delta = (idle_delta > elapsed_delta) ? elapsed_delta : idle_delta;
> +		load = 100 * (elapsed_delta - idle_delta) / elapsed_delta;
> +		if (load >= load_thresh)
> +			busy_nr++;
> +	}
> +
> +	return (busy_nr >= num_cpus) ? true : false;
> +}
> +
>  static void acpi_pad_idle_cpus(unsigned int num_cpus)
>  {
>  	get_online_cpus();
>  
>  	num_cpus = min_t(unsigned int, num_cpus, num_online_cpus());
> -	set_power_saving_task_num(num_cpus);
> +	if (idle_nr_valid(num_cpus))
> +		set_power_saving_task_num(num_cpus);
>  
>  	put_online_cpus();
>  }
> -- 
> 2.7.4
> 
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