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From:   "Rafael J. Wysocki" <rafael@kernel.org>
Date:   Mon, 6 Aug 2018 11:36:02 +0200
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Subject: Re: [PATCH v8 04/26] PM / Domains: Add support for CPU devices to genpd
To:     Ulf Hansson <ulf.hansson@linaro.org>
Cc:     "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Sudeep Holla <sudeep.holla@arm.com>,
        Lorenzo Pieralisi <Lorenzo.Pieralisi@arm.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Linux PM <linux-pm@vger.kernel.org>,
        Kevin Hilman <khilman@kernel.org>,
        Lina Iyer <ilina@codeaurora.org>,
        Lina Iyer <lina.iyer@linaro.org>,
        Rob Herring <robh+dt@kernel.org>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Stephen Boyd <sboyd@kernel.org>,
        Juri Lelli <juri.lelli@arm.com>,
        Geert Uytterhoeven <geert+renesas@glider.be>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        linux-arm-msm <linux-arm-msm@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Fri, Aug 3, 2018 at 1:43 PM, Ulf Hansson <ulf.hansson@linaro.org> wrote:
> On 19 July 2018 at 12:25, Rafael J. Wysocki <rjw@rjwysocki.net> wrote:
>> On Wednesday, June 20, 2018 7:22:04 PM CEST Ulf Hansson wrote:
>>> To enable a device belonging to a CPU to be attached to a PM domain managed
>>> by genpd, let's do a few changes to genpd as to make it convenient to
>>> manage the specifics around CPUs.
>>>
>>> First, as to be able to quickly find out what CPUs that are attached to a
>>> genpd, which typically becomes useful from a genpd governor as following
>>> changes is about to show, let's add a cpumask 'cpus' to the struct
>>> generic_pm_domain.
>>>
>>> At the point when a device that belongs to a CPU, is attached/detached to
>>> its corresponding PM domain via genpd_add_device(), let's update the
>>> cpumask in genpd->cpus. Moreover, propagate the update of the cpumask to
>>> the master domains, which makes the genpd->cpus to contain a cpumask that
>>> hierarchically reflect all CPUs for a genpd, including CPUs attached to
>>> subdomains.
>>>
>>> Second, to unconditionally manage CPUs and the cpumask in genpd->cpus, is
>>> unnecessary for cases when only non-CPU devices are parts of a genpd.
>>> Let's avoid this by adding a new configuration bit, GENPD_FLAG_CPU_DOMAIN.
>>> Clients must set the bit before they call pm_genpd_init(), as to instruct
>>> genpd that it shall deal with CPUs and thus manage the cpumask in
>>> genpd->cpus.
>>>
>>> Cc: Lina Iyer <ilina@codeaurora.org>
>>> Co-developed-by: Lina Iyer <lina.iyer@linaro.org>
>>> Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
>>> ---
>>>  drivers/base/power/domain.c | 69 ++++++++++++++++++++++++++++++++++++-
>>>  include/linux/pm_domain.h   |  3 ++
>>>  2 files changed, 71 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
>>> index 21d298e1820b..6149ce0bfa7b 100644
>>> --- a/drivers/base/power/domain.c
>>> +++ b/drivers/base/power/domain.c
>>> @@ -20,6 +20,7 @@
>>>  #include <linux/sched.h>
>>>  #include <linux/suspend.h>
>>>  #include <linux/export.h>
>>> +#include <linux/cpu.h>
>>>
>>>  #include "power.h"
>>>
>>> @@ -126,6 +127,7 @@ static const struct genpd_lock_ops genpd_spin_ops = {
>>>  #define genpd_is_irq_safe(genpd)     (genpd->flags & GENPD_FLAG_IRQ_SAFE)
>>>  #define genpd_is_always_on(genpd)    (genpd->flags & GENPD_FLAG_ALWAYS_ON)
>>>  #define genpd_is_active_wakeup(genpd)        (genpd->flags & GENPD_FLAG_ACTIVE_WAKEUP)
>>> +#define genpd_is_cpu_domain(genpd)   (genpd->flags & GENPD_FLAG_CPU_DOMAIN)
>>>
>>>  static inline bool irq_safe_dev_in_no_sleep_domain(struct device *dev,
>>>               const struct generic_pm_domain *genpd)
>>> @@ -1377,6 +1379,62 @@ static void genpd_free_dev_data(struct device *dev,
>>>       dev_pm_put_subsys_data(dev);
>>>  }
>>>
>>> +static void __genpd_update_cpumask(struct generic_pm_domain *genpd,
>>> +                                int cpu, bool set, unsigned int depth)
>>> +{
>>> +     struct gpd_link *link;
>>> +
>>> +     if (!genpd_is_cpu_domain(genpd))
>>> +             return;
>>> +
>>> +     list_for_each_entry(link, &genpd->slave_links, slave_node) {
>>> +             struct generic_pm_domain *master = link->master;
>>> +
>>> +             genpd_lock_nested(master, depth + 1);
>>> +             __genpd_update_cpumask(master, cpu, set, depth + 1);
>>> +             genpd_unlock(master);
>>> +     }
>>> +
>>> +     if (set)
>>> +             cpumask_set_cpu(cpu, genpd->cpus);
>>> +     else
>>> +             cpumask_clear_cpu(cpu, genpd->cpus);
>>> +}
>>
>> As noted elsewhere, there is a concern about the possible weight of this
>> cpumask and I think that it would be good to explicitly put a limit on it.
>
> I have been digesting your comments on the series, but wonder if this
> is still a relevant concern?

Well, there are systems with very large cpumasks and it is sort of
good to have that in mind when designing any code using them.