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

[joeyli]

Hi Yu Chen,

Thanks for your response!

On Tue, Dec 11, 2018 at 11:12:21AM +0800, Yu Chen wrote:
> Hi Joey,
> On Mon, Dec 10, 2018 at 02:31:53PM +0800, joeyli wrote:
> > 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@xxxxxxxxxx>
> > > Suggested-by: Len Brown <lenb@xxxxxxxxxx>
> > > Cc: "Rafael J. Wysocki" <rjw@xxxxxxxxxxxxx>
> > > Cc: Lenny Szubowicz <lszubowi@xxxxxxxxxx>
> > > Cc: Len Brown <lenb@xxxxxxxxxx>
> > > Cc: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
> > > Cc: Rui Zhang <rui.zhang@xxxxxxxxx>
> > > Cc: linux-acpi@xxxxxxxxxxxxxxx
> > > Signed-off-by: Chen Yu <yu.c.chen@xxxxxxxxx>
> > 
> > Do you have any news for this patch? Why it did not merged by kernel
> > maineline?
> > 
> We are evaluating if this could be integrated into idle injection framework.
> May I know if there's any requirement/background from SUSE on this?
> 

I am also looking at your patch and idle injection framework. Currently I do not
have good suggestion for your patches yet. But I will try to ready my knowledge when
you send out new version.

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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