From: "Rafael J. Wysocki" <rafael@kernel.org>
To: Ulf Hansson <ulf.hansson@linaro.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
Lorenzo Pieralisi <Lorenzo.Pieralisi@arm.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Geert Uytterhoeven <geert+renesas@glider.be>,
Linux PM <linux-pm@vger.kernel.org>,
Stephen Boyd <sboyd@kernel.org>,
Viresh Kumar <viresh.kumar@linaro.org>,
linux-arm-msm <linux-arm-msm@vger.kernel.org>,
Daniel Lezcano <daniel.lezcano@linaro.org>,
"Rafael J. Wysocki" <rjw@rjwysocki.net>,
Kevin Hilman <khilman@kernel.org>,
Lina Iyer <ilina@codeaurora.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Frederic Weisbecker <fweisbec@gmail.com>,
Tony Lindgren <tony@atomide.com>,
Lina Iyer <lina.iyer@linaro.org>,
Sudeep Holla <sudeep.holla@arm.com>,
Thomas Gleixner <tglx@linutronix.de>,
"Raju P . L . S . S . S . N" <rplsssn@codeaurora.org>,
Ingo Molnar <mingo@kernel.org>,
Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v10 03/27] timer: Export next wakeup time of a CPU
Date: Wed, 16 Jan 2019 11:59:40 +0100 [thread overview]
Message-ID: <CAJZ5v0iY7j5SThQhtq5xP+g5yNiHQ+cMWxq-tdVh3t5wJ_s3Tw@mail.gmail.com> (raw)
In-Reply-To: <CAPDyKFqQQnMKFNpGyi_dkP_Rm8qo-1WjPfVkp2unOxyXRa2wbA@mail.gmail.com>
On Wed, Jan 16, 2019 at 8:58 AM Ulf Hansson <ulf.hansson@linaro.org> wrote:
>
> On Fri, 11 Jan 2019 at 12:07, Rafael J. Wysocki <rjw@rjwysocki.net> wrote:
> >
> > On Thursday, November 29, 2018 6:46:36 PM CET Ulf Hansson wrote:
> > > From: Lina Iyer <lina.iyer@linaro.org>
> > >
> > > Knowing the sleep duration of CPUs, is known to be needed while selecting
> > > the most energy efficient idle state for a CPU or a group of CPUs.
> > >
> > > However, to be able to compute the sleep duration, we need to know at what
> > > time the next expected wakeup is for the CPU. Therefore, let's export this
> > > information via a new function, tick_nohz_get_next_wakeup(). Following
> > > changes make use of it.
> > >
> > > Cc: Thomas Gleixner <tglx@linutronix.de>
> > > Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
> > > Cc: Lina Iyer <ilina@codeaurora.org>
> > > Cc: Frederic Weisbecker <fweisbec@gmail.com>
> > > Cc: Ingo Molnar <mingo@kernel.org>
> > > Signed-off-by: Lina Iyer <lina.iyer@linaro.org>
> > > Co-developed-by: Ulf Hansson <ulf.hansson@linaro.org>
> > > Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
> > > ---
> > >
> > > Changes in v10:
> > > - Updated function header of tick_nohz_get_next_wakeup().
> > >
> > > ---
> > > include/linux/tick.h | 8 ++++++++
> > > kernel/time/tick-sched.c | 13 +++++++++++++
> > > 2 files changed, 21 insertions(+)
> > >
> > > diff --git a/include/linux/tick.h b/include/linux/tick.h
> > > index 55388ab45fd4..e48f6b26b425 100644
> > > --- a/include/linux/tick.h
> > > +++ b/include/linux/tick.h
> > > @@ -125,6 +125,7 @@ extern bool tick_nohz_idle_got_tick(void);
> > > extern ktime_t tick_nohz_get_sleep_length(ktime_t *delta_next);
> > > extern unsigned long tick_nohz_get_idle_calls(void);
> > > extern unsigned long tick_nohz_get_idle_calls_cpu(int cpu);
> > > +extern ktime_t tick_nohz_get_next_wakeup(int cpu);
> > > extern u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time);
> > > extern u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time);
> > >
> > > @@ -151,6 +152,13 @@ static inline ktime_t tick_nohz_get_sleep_length(ktime_t *delta_next)
> > > *delta_next = TICK_NSEC;
> > > return *delta_next;
> > > }
> > > +
> > > +static inline ktime_t tick_nohz_get_next_wakeup(int cpu)
> > > +{
> > > + /* Next wake up is the tick period, assume it starts now */
> > > + return ktime_add(ktime_get(), TICK_NSEC);
> > > +}
> > > +
> > > static inline u64 get_cpu_idle_time_us(int cpu, u64 *unused) { return -1; }
> > > static inline u64 get_cpu_iowait_time_us(int cpu, u64 *unused) { return -1; }
> > >
> > > diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
> > > index 69e673b88474..7a9166506503 100644
> > > --- a/kernel/time/tick-sched.c
> > > +++ b/kernel/time/tick-sched.c
> > > @@ -1089,6 +1089,19 @@ unsigned long tick_nohz_get_idle_calls(void)
> > > return ts->idle_calls;
> > > }
> > >
> > > +/**
> > > + * tick_nohz_get_next_wakeup - return the next wake up of the CPU
> > > + * @cpu: the particular CPU to get next wake up for
> > > + *
> > > + * Called for idle CPUs only.
> > > + */
> > > +ktime_t tick_nohz_get_next_wakeup(int cpu)
> > > +{
> > > + struct clock_event_device *dev = per_cpu(tick_cpu_device.evtdev, cpu);
> > > +
> > > + return dev->next_event;
> > > +}
> > > +
> > > static void tick_nohz_account_idle_ticks(struct tick_sched *ts)
> > > {
> > > #ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
> > >
> >
> > Well, I have concerns regarding this one.
> >
> > I don't believe it is valid to call this new function for non-idle CPUs and
> > the kerneldoc kind of says so, but the next patch doesn't actually prevent
> > it from being called for a non-idle CPU (at the time it is called in there
> > the target CPU may not be idle any more AFAICS).
>
> You are correct, but let me clarify things.
>
> We are calling this new API from the new genpd governor, which may
> have a cpumask indicating there is more than one CPU attached to its
> PM domain+sub-PM domains. In other words, we may call the API for
> another CPU than the one we are executing on.
>
> When the new genpd governor is called, all CPUs in the cpumask of the
> genpd in question, are already runtime suspended and will remain so
> throughout the decisions made by the governor.
>
> However, because of the race condition, which needs to be manged by
> the genpd backend driver and its corresponding FW, one of the CPU in
> the genpd cpumask could potentially wake up from idle when the genpd
> governor runs. However, as a part of exiting from idle, that CPU needs
> to wait for the call to pm_runtime_get_sync() to return before
> completing the exit patch of idle. This also means waiting for the
> genpd governor to finish.
OK, so the CPU spins on a spin lock inside of the idle loop with interrupts off.
> The point is, no matter what decision the governor takes under these
> circumstances, the genpd backend driver and its FW must manage this
> race condition during the last man standing. For PSCI OSI mode, it
> means that if a cluster idle state is suggested by Linux during these
> circumstances, it must be prevented and aborted.
I would suggest putting a comment to explain that somewhere as it is
not really obvious.
> >
> > In principle, the cpuidle core can store this value, say in struct
> > cpuidle_device of the given CPU, and expose a helper to access it from
> > genpd, but that would be extra overhead totally unnecessary on everthing
> > that doesn't use genpd for cpuidle.
> >
> > So maybe the driver could store it in its ->enter callback? After all,
> > the driver knows that genpd is going to be used later.
>
> This would work, but it wouldn't really change much when it comes to
> the race condition described above.
No, it wouldn't make the race go away.
> Of course it would turn the code
> into being more cpuidle specific, which seems reasonable to me.
>
> Anyway, if I understand your suggestion, in principle it means
> changing $subject patch in such way that the API should not take "int
> cpu" as an in-parameter, but instead only use __this_cpu() to read out
> the next event for current idle CPU.
Yes.
> Additionally, we need another new cpuidle API, which genpd can call to
> retrieve a new per CPU "next event data" stored by the cpuidle driver
> from its ->enter() callback. Is this a correct interpretation of your
> suggestion?
Yes, it is.
Generally, something like "cpuidle, give me the wakeup time of this
CPU". And it may very well give you 0 if the CPU has woken up
already. :-)
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2019-01-16 11:00 UTC|newest]
Thread overview: 73+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-29 17:46 [PATCH v10 00/27] PM / Domains: Support hierarchical CPU arrangement (PSCI/ARM) Ulf Hansson
2018-11-29 17:46 ` [PATCH v10 01/27] PM / Domains: Add generic data pointer to genpd_power_state struct Ulf Hansson
2018-12-18 10:39 ` Daniel Lezcano
2018-12-18 11:53 ` Ulf Hansson
2019-01-11 10:52 ` Rafael J. Wysocki
2018-11-29 17:46 ` [PATCH v10 02/27] PM / Domains: Add support for CPU devices to genpd Ulf Hansson
2018-12-19 9:53 ` Daniel Lezcano
2018-12-19 10:02 ` Ulf Hansson
2019-01-11 10:54 ` Rafael J. Wysocki
2018-11-29 17:46 ` [PATCH v10 03/27] timer: Export next wakeup time of a CPU Ulf Hansson
2019-01-11 11:06 ` Rafael J. Wysocki
2019-01-16 7:57 ` Ulf Hansson
2019-01-16 10:59 ` Rafael J. Wysocki [this message]
2019-01-16 12:00 ` Ulf Hansson
2019-01-25 10:04 ` Ulf Hansson
2019-01-25 10:18 ` Rafael J. Wysocki
2018-11-29 17:46 ` [PATCH v10 04/27] PM / Domains: Add genpd governor for CPUs Ulf Hansson
2018-12-19 9:54 ` Daniel Lezcano
2018-12-19 10:09 ` Ulf Hansson
2018-11-29 17:46 ` [PATCH v10 05/27] dt: psci: Update DT bindings to support hierarchical PSCI states Ulf Hansson
2018-11-29 17:46 ` [PATCH v10 06/27] of: base: Add of_get_cpu_state_node() to get idle states for a CPU node Ulf Hansson
2018-12-19 11:05 ` Daniel Lezcano
2018-11-29 17:46 ` [PATCH v10 07/27] cpuidle: dt: Support hierarchical CPU idle states Ulf Hansson
2018-12-19 11:20 ` Daniel Lezcano
2018-11-29 17:46 ` [PATCH v10 08/27] ARM/ARM64: cpuidle: Let back-end init ops take the driver as input Ulf Hansson
2018-11-29 17:46 ` [PATCH v10 09/27] drivers: firmware: psci: Move psci to separate directory Ulf Hansson
2018-11-29 17:46 ` [PATCH v10 10/27] MAINTAINERS: Update files for PSCI Ulf Hansson
2018-11-29 17:46 ` [PATCH v10 11/27] drivers: firmware: psci: Split psci_dt_cpu_init_idle() Ulf Hansson
2018-11-29 17:46 ` [PATCH v10 12/27] drivers: firmware: psci: Simplify state node parsing Ulf Hansson
2018-11-29 17:46 ` [PATCH v10 13/27] drivers: firmware: psci: Support hierarchical CPU idle states Ulf Hansson
2018-12-19 12:11 ` Daniel Lezcano
2018-12-19 12:53 ` Ulf Hansson
2018-11-29 17:46 ` [PATCH v10 14/27] drivers: firmware: psci: Simplify error path of psci_dt_init() Ulf Hansson
2018-12-19 12:08 ` Daniel Lezcano
2018-11-29 17:46 ` [PATCH v10 15/27] drivers: firmware: psci: Announce support for OS initiated suspend mode Ulf Hansson
2018-12-20 13:11 ` Daniel Lezcano
2018-11-29 17:46 ` [PATCH v10 16/27] drivers: firmware: psci: Prepare to use " Ulf Hansson
2018-12-20 14:08 ` Daniel Lezcano
2018-12-20 15:41 ` Ulf Hansson
2018-12-20 17:16 ` Daniel Lezcano
2018-11-29 17:46 ` [PATCH v10 17/27] drivers: firmware: psci: Prepare to support PM domains Ulf Hansson
2018-12-20 14:19 ` Daniel Lezcano
2018-12-20 15:49 ` Ulf Hansson
2018-12-20 18:06 ` Daniel Lezcano
2018-12-20 21:37 ` Ulf Hansson
2018-12-21 7:15 ` Daniel Lezcano
2018-11-29 17:46 ` [PATCH v10 18/27] drivers: firmware: psci: Add support for PM domains using genpd Ulf Hansson
2018-12-03 16:37 ` Lina Iyer
2018-12-03 20:03 ` Ulf Hansson
2018-12-20 14:35 ` Daniel Lezcano
2018-12-20 21:09 ` Ulf Hansson
2018-11-29 17:46 ` [PATCH v10 19/27] drivers: firmware: psci: Add hierarchical domain idle states converter Ulf Hansson
2018-11-29 17:46 ` [PATCH v10 20/27] drivers: firmware: psci: Introduce psci_dt_topology_init() Ulf Hansson
2018-11-29 17:46 ` [PATCH v10 21/27] drivers: firmware: psci: Add a helper to attach a CPU to its PM domain Ulf Hansson
2018-12-04 18:45 ` Lina Iyer
2018-12-06 9:15 ` Ulf Hansson
2018-11-29 17:46 ` [PATCH v10 22/27] drivers: firmware: psci: Attach the CPU's device " Ulf Hansson
2018-11-29 17:46 ` [PATCH v10 23/27] drivers: firmware: psci: Manage runtime PM in the idle path for CPUs Ulf Hansson
2018-11-29 17:46 ` [PATCH v10 24/27] drivers: firmware: psci: Support CPU hotplug for the hierarchical model Ulf Hansson
2018-11-29 22:31 ` Lina Iyer
2018-11-30 8:25 ` Ulf Hansson
2018-11-30 20:57 ` Lina Iyer
2018-12-19 11:17 ` Lorenzo Pieralisi
2018-12-19 11:47 ` Ulf Hansson
2018-11-29 17:46 ` [PATCH v10 25/27] arm64: kernel: Respect the hierarchical CPU topology in DT for PSCI Ulf Hansson
2018-11-29 17:46 ` [PATCH v10 26/27] arm64: dts: Convert to the hierarchical CPU topology layout for MSM8916 Ulf Hansson
2018-11-29 17:47 ` [PATCH v10 27/27] arm64: dts: hikey: Convert to the hierarchical CPU topology layout Ulf Hansson
2018-12-17 16:12 ` [PATCH v10 00/27] PM / Domains: Support hierarchical CPU arrangement (PSCI/ARM) Ulf Hansson
2019-01-11 11:08 ` Rafael J. Wysocki
2019-01-03 12:06 ` Sudeep Holla
2019-01-16 9:10 ` Ulf Hansson
2019-01-17 17:44 ` Sudeep Holla
2019-01-18 11:56 ` Ulf Hansson
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CAJZ5v0iY7j5SThQhtq5xP+g5yNiHQ+cMWxq-tdVh3t5wJ_s3Tw@mail.gmail.com \
--to=rafael@kernel.org \
--cc=Lorenzo.Pieralisi@arm.com \
--cc=daniel.lezcano@linaro.org \
--cc=fweisbec@gmail.com \
--cc=geert+renesas@glider.be \
--cc=ilina@codeaurora.org \
--cc=khilman@kernel.org \
--cc=lina.iyer@linaro.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-arm-msm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-pm@vger.kernel.org \
--cc=mark.rutland@arm.com \
--cc=mingo@kernel.org \
--cc=rjw@rjwysocki.net \
--cc=rplsssn@codeaurora.org \
--cc=sboyd@kernel.org \
--cc=sudeep.holla@arm.com \
--cc=tglx@linutronix.de \
--cc=tony@atomide.com \
--cc=ulf.hansson@linaro.org \
--cc=vincent.guittot@linaro.org \
--cc=viresh.kumar@linaro.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).