linux-kernel - Re: [PATCH v8 04/26] PM / Domains: Add support for CPU devices to genpd

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Date:   Fri, 24 Aug 2018 08:47:21 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Sudeep Holla <sudeep.holla@....com>,
        Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
        Mark Rutland <mark.rutland@....com>,
        Linux PM <linux-pm@...r.kernel.org>,
        Kevin Hilman <khilman@...nel.org>,
        Lina Iyer <ilina@...eaurora.org>,
        Lina Iyer <lina.iyer@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Juri Lelli <juri.lelli@....com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v8 04/26] PM / Domains: Add support for CPU devices to genpd

On 6 August 2018 at 11:36, Rafael J. Wysocki <rafael@...nel.org> wrote:
> On Fri, Aug 3, 2018 at 1:43 PM, Ulf Hansson <ulf.hansson@...aro.org> wrote:
>> On 19 July 2018 at 12:25, Rafael J. Wysocki <rjw@...ysocki.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@...eaurora.org>
>>>> Co-developed-by: Lina Iyer <lina.iyer@...aro.org>
>>>> Signed-off-by: Ulf Hansson <ulf.hansson@...aro.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.

Right.

So, if I avoid allocating the cpumask for those genpd structures that
doesn't need it (those not having GENPD_FLAG_CPU_DOMAIN set), would
that be sufficient to deal with your concern?

Kind regards
Uffe