Re: [PATCH v9 02/15] sched/cpufreq: Prepare schedutil for Energy Aware Scheduling

[Quentin Perret]

On Tuesday 20 Nov 2018 at 16:25:14 (+0100), Peter Zijlstra wrote:
> On Tue, Nov 20, 2018 at 10:16:02AM +0530, Viresh Kumar wrote:
> > On 19-11-18, 14:18, Quentin Perret wrote:
> > > @@ -223,20 +222,33 @@ static unsigned long sugov_get_util(struct sugov_cpu *sg_cpu)
> > 
> > > -	if ((util + cpu_util_dl(rq)) >= max)
> > > -		return max;
> > > +	if (type == FREQUENCY_UTIL) {
> > > +		/*
> > > +		 * For frequency selection we do not make cpu_util_dl() a
> > > +		 * permanent part of this sum because we want to use
> > > +		 * cpu_bw_dl() later on, but we need to check if the
> > > +		 * CFS+RT+DL sum is saturated (ie. no idle time) such
> > > +		 * that we select f_max when there is no idle time.
> > > +		 *
> > > +		 * NOTE: numerical errors or stop class might cause us
> > > +		 * to not quite hit saturation when we should --
> > > +		 * something for later.
> > > +		 */
> > > +
> > > +		if ((util + cpu_util_dl(rq)) >= max)
> > > +			return max;
> > > +	} else {
> > > +		/*
> > > +		 * OTOH, for energy computation we need the estimated
> > > +		 * running time, so include util_dl and ignore dl_bw.
> > > +		 */
> > > +		util += cpu_util_dl(rq);
> > > +		if (util >= max)
> > > +			return max;
> > > +	}
> > 
> > Maybe write above as:
> > 
> >         dl_util = cpu_util_dl(rq);
> > 
> >         if ((util + dl_util) >= max)
> >                 return max;
> > 
> > 	if (type != FREQUENCY_UTIL)
> > 		util += dl_util;
> > 
> > 
> > as both the if/else parts were doing almost the same thing.
> 
> A little like so ?
> 
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -201,8 +201,8 @@ static unsigned int get_next_freq(struct
>  unsigned long schedutil_freq_util(int cpu, unsigned long util_cfs,
>  				  unsigned long max, enum schedutil_type type)
>  {
> +	unsigned long dl_util, util, irq;
>  	struct rq *rq = cpu_rq(cpu);
> -	unsigned long util, irq;
>  
>  	if (type == FREQUENCY_UTIL && rt_rq_is_runnable(&rq->rt))
>  		return max;
> @@ -225,30 +225,26 @@ unsigned long schedutil_freq_util(int cp
>  	util = util_cfs;
>  	util += cpu_util_rt(rq);
>  
> -	if (type == FREQUENCY_UTIL) {
> -		/*
> -		 * For frequency selection we do not make cpu_util_dl() a
> -		 * permanent part of this sum because we want to use
> -		 * cpu_bw_dl() later on, but we need to check if the
> -		 * CFS+RT+DL sum is saturated (ie. no idle time) such
> -		 * that we select f_max when there is no idle time.
> -		 *
> -		 * NOTE: numerical errors or stop class might cause us
> -		 * to not quite hit saturation when we should --
> -		 * something for later.
> -		 */
> -
> -		if ((util + cpu_util_dl(rq)) >= max)
> -			return max;
> -	} else {
> -		/*
> -		 * OTOH, for energy computation we need the estimated
> -		 * running time, so include util_dl and ignore dl_bw.
> -		 */
> -		util += cpu_util_dl(rq);
> -		if (util >= max)
> -			return max;
> -	}
> +	dl_util = cpu_util_dl(rq);
> +
> +	/*
> +	 * NOTE: numerical errors or stop class might cause us to not quite hit
> +	 * saturation when we should -- something for later.
> +	 */
> +	if (util + dl_util > max)
> +		return max;
> +
> +	/*
> +	 * For frequency selection we do not make cpu_util_dl() a permanent
> +	 * part of this sum because we want to use cpu_bw_dl() later on, but we
> +	 * need to check if the CFS+RT+DL sum is saturated (ie. no idle time)
> +	 * such that we select f_max when there is no idle time.

We probably want move that paragraph to the comment above no ? Other
than that, the change LGTM.

> +	 *
> +	 * OTOH, for energy computation we need the estimated running time, so
> +	 * do include util_dl and ignore dl_bw.
> +	 */
> +	if (type == ENERGY_UTIL)
> +		util += dl_util;
>  
>  	/*
>  	 * There is still idle time; further improve the number by using the
> @@ -262,21 +258,18 @@ unsigned long schedutil_freq_util(int cp
>  	util = scale_irq_capacity(util, irq, max);
>  	util += irq;
>  
> -	if (type == FREQUENCY_UTIL) {
> -		/*
> -		 * Bandwidth required by DEADLINE must always be granted
> -		 * while, for FAIR and RT, we use blocked utilization of
> -		 * IDLE CPUs as a mechanism to gracefully reduce the
> -		 * frequency when no tasks show up for longer periods of
> -		 * time.
> -		 *
> -		 * Ideally we would like to set bw_dl as min/guaranteed
> -		 * freq and util + bw_dl as requested freq. However,
> -		 * cpufreq is not yet ready for such an interface. So,
> -		 * we only do the latter for now.
> -		 */
> +	/*
> +	 * Bandwidth required by DEADLINE must always be granted while, for
> +	 * FAIR and RT, we use blocked utilization of IDLE CPUs as a mechanism
> +	 * to gracefully reduce the frequency when no tasks show up for longer
> +	 * periods of time.
> +	 *
> +	 * Ideally we would like to set bw_dl as min/guaranteed freq and util +
> +	 * bw_dl as requested freq. However, cpufreq is not yet ready for such
> +	 * an interface. So, we only do the latter for now.
> +	 */
> +	if (type == FREQUENCY_UTIL)
>  		util += cpu_bw_dl(rq);
> -	}
>  
>  	return min(max, util);
>  }

Thanks,
Quentin