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Message-ID: <20171205150935.GL31247@e110439-lin>
Date: Tue, 5 Dec 2017 15:09:35 +0000
From: Patrick Bellasi <patrick.bellasi@....com>
To: Juri Lelli <juri.lelli@...hat.com>
Cc: peterz@...radead.org, mingo@...hat.com, rjw@...ysocki.net,
viresh.kumar@...aro.org, linux-kernel@...r.kernel.org,
linux-pm@...r.kernel.org, tglx@...utronix.de,
vincent.guittot@...aro.org, rostedt@...dmis.org,
luca.abeni@...tannapisa.it, claudio@...dence.eu.com,
tommaso.cucinotta@...tannapisa.it, bristot@...hat.com,
mathieu.poirier@...aro.org, tkjos@...roid.com, joelaf@...gle.com,
morten.rasmussen@....com, dietmar.eggemann@....com,
alessio.balsini@....com, Juri Lelli <juri.lelli@....com>,
Ingo Molnar <mingo@...nel.org>,
"Rafael J . Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: [RFC PATCH v2 1/8] sched/cpufreq_schedutil: make use of DEADLINE
utilization signal
Hi Juri,
On 04-Dec 11:23, Juri Lelli wrote:
> From: Juri Lelli <juri.lelli@....com>
>
> SCHED_DEADLINE tracks active utilization signal with a per dl_rq
> variable named running_bw.
>
> Make use of that to drive cpu frequency selection: add up FAIR and
> DEADLINE contribution to get the required CPU capacity to handle both
> requirements (while RT still selects max frequency).
>
> Co-authored-by: Claudio Scordino <claudio@...dence.eu.com>
> Signed-off-by: Juri Lelli <juri.lelli@....com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> Cc: Viresh Kumar <viresh.kumar@...aro.org>
> Cc: Luca Abeni <luca.abeni@...tannapisa.it>
> Acked-by: Viresh Kumar <viresh.kumar@...aro.org>
> ---
> include/linux/sched/cpufreq.h | 2 --
> kernel/sched/cpufreq_schedutil.c | 25 +++++++++++++++----------
> 2 files changed, 15 insertions(+), 12 deletions(-)
>
> diff --git a/include/linux/sched/cpufreq.h b/include/linux/sched/cpufreq.h
> index d1ad3d825561..0b55834efd46 100644
> --- a/include/linux/sched/cpufreq.h
> +++ b/include/linux/sched/cpufreq.h
> @@ -12,8 +12,6 @@
> #define SCHED_CPUFREQ_DL (1U << 1)
> #define SCHED_CPUFREQ_IOWAIT (1U << 2)
>
> -#define SCHED_CPUFREQ_RT_DL (SCHED_CPUFREQ_RT | SCHED_CPUFREQ_DL)
> -
> #ifdef CONFIG_CPU_FREQ
> struct update_util_data {
> void (*func)(struct update_util_data *data, u64 time, unsigned int flags);
> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> index 2f52ec0f1539..de1ad1fffbdc 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -179,12 +179,17 @@ static unsigned int get_next_freq(struct sugov_policy *sg_policy,
> static void sugov_get_util(unsigned long *util, unsigned long *max, int cpu)
> {
> struct rq *rq = cpu_rq(cpu);
> - unsigned long cfs_max;
> + unsigned long dl_util = (rq->dl.running_bw * SCHED_CAPACITY_SCALE)
> + >> BW_SHIFT;
What about using a pair of getter methods (e.g. cpu_util_{cfs,dl}) to
be defined in kernel/sched/sched.h?
This would help to hide class-specific signals mangling from cpufreq.
And here we can have something "more abstract" like:
unsigned long util_cfs = cpu_util_cfs(rq);
unsigned long util_dl = cpu_util_dl(rq);
>
> - cfs_max = arch_scale_cpu_capacity(NULL, cpu);
> + *max = arch_scale_cpu_capacity(NULL, cpu);
>
> - *util = min(rq->cfs.avg.util_avg, cfs_max);
> - *max = cfs_max;
> + /*
> + * Ideally we would like to set util_dl as min/guaranteed freq and
> + * util_cfs + util_dl as requested freq. However, cpufreq is not yet
> + * ready for such an interface. So, we only do the latter for now.
> + */
Maybe I don't completely get the above comment, but to me it is not
really required.
When you say that "util_dl" should be set to a min/guaranteed freq
are you not actually talking about a DL implementation detail?
>From the cpufreq standpoint instead, we should always set a capacity
which can accommodate util_dl + util_cfs.
We don't care about the meaning of util_dl and we should always assume
(by default) that the signal is properly updated by the scheduling
class... which unfortunately does not always happen for CFS.
> + *util = min(rq->cfs.avg.util_avg + dl_util, *max);
With the above proposal, here also we will have:
*util = min(util_cfs + util_dl, *max);
> }
>
> static void sugov_set_iowait_boost(struct sugov_cpu *sg_cpu, u64 time,
> @@ -272,7 +277,7 @@ static void sugov_update_single(struct update_util_data *hook, u64 time,
>
> busy = sugov_cpu_is_busy(sg_cpu);
>
> - if (flags & SCHED_CPUFREQ_RT_DL) {
> + if (flags & SCHED_CPUFREQ_RT) {
> next_f = policy->cpuinfo.max_freq;
> } else {
> sugov_get_util(&util, &max, sg_cpu->cpu);
> @@ -317,7 +322,7 @@ static unsigned int sugov_next_freq_shared(struct sugov_cpu *sg_cpu, u64 time)
> j_sg_cpu->iowait_boost_pending = false;
> continue;
> }
> - if (j_sg_cpu->flags & SCHED_CPUFREQ_RT_DL)
> + if (j_sg_cpu->flags & SCHED_CPUFREQ_RT)
> return policy->cpuinfo.max_freq;
>
> j_util = j_sg_cpu->util;
> @@ -353,7 +358,7 @@ static void sugov_update_shared(struct update_util_data *hook, u64 time,
> sg_cpu->last_update = time;
>
> if (sugov_should_update_freq(sg_policy, time)) {
> - if (flags & SCHED_CPUFREQ_RT_DL)
> + if (flags & SCHED_CPUFREQ_RT)
> next_f = sg_policy->policy->cpuinfo.max_freq;
> else
> next_f = sugov_next_freq_shared(sg_cpu, time);
> @@ -383,9 +388,9 @@ static void sugov_irq_work(struct irq_work *irq_work)
> sg_policy = container_of(irq_work, struct sugov_policy, irq_work);
>
> /*
> - * For RT and deadline tasks, the schedutil governor shoots the
> - * frequency to maximum. Special care must be taken to ensure that this
> - * kthread doesn't result in the same behavior.
> + * For RT tasks, the schedutil governor shoots the frequency to maximum.
> + * Special care must be taken to ensure that this kthread doesn't result
> + * in the same behavior.
> *
> * This is (mostly) guaranteed by the work_in_progress flag. The flag is
> * updated only at the end of the sugov_work() function and before that
> --
> 2.14.3
>
--
#include <best/regards.h>
Patrick Bellasi
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