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Message-ID: <CAPDyKFrL63Jv4_cUbrjAaU4UtNNDVMpALt41Mu6NbGcAefmWUA@mail.gmail.com>
Date: Tue, 8 Jul 2025 16:41:25 +0200
From: Ulf Hansson <ulf.hansson@...aro.org>
To: Maulik Shah <maulik.shah@....qualcomm.com>
Cc: linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH] pmdomain: governor: Consider CPU latency tolerance from pm_domain_cpu_gov
On Tue, 8 Jul 2025 at 07:15, Maulik Shah <maulik.shah@....qualcomm.com> wrote:
>
> pm_domain_cpu_gov is selecting a cluster idle state but does not consider
> latency tolerance of child CPUs. This results in deeper cluster idle state
> whose latency does not meet latency tolerance requirement.
>
> Select deeper idle state only if global and device latency tolerance of all
> child CPUs meet.
>
> Test results on SM8750 with 300 usec PM-QoS on CPU0 which is less than
> domain idle state entry (2150) + exit (1983) usec latency mentioned in
> devicetree, demonstrate the issue.
>
> # echo 300 > /sys/devices/system/cpu/cpu0/power/pm_qos_resume_latency_us
>
> Before: (Usage is incrementing)
> ======
> # cat /sys/kernel/debug/pm_genpd/power-domain-cluster0/idle_states
> State Time Spent(ms) Usage Rejected Above Below
> S0 29817 537 8 270 0
>
> # cat /sys/kernel/debug/pm_genpd/power-domain-cluster0/idle_states
> State Time Spent(ms) Usage Rejected Above Below
> S0 30348 542 8 271 0
>
> After: (Usage is not incrementing due to latency tolerance)
> ======
> # cat /sys/kernel/debug/pm_genpd/power-domain-cluster0/idle_states
> State Time Spent(ms) Usage Rejected Above Below
> S0 39319 626 14 307 0
>
> # cat /sys/kernel/debug/pm_genpd/power-domain-cluster0/idle_states
> State Time Spent(ms) Usage Rejected Above Below
> S0 39319 626 14 307 0
>
> Signed-off-by: Maulik Shah <maulik.shah@....qualcomm.com>
Thanks for posting this! I am actually carrying a local patch in my
tree for this, just haven't reached the point of posting it. :-)
> ---
> drivers/pmdomain/governor.c | 18 ++++++++++++++++--
> 1 file changed, 16 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/pmdomain/governor.c b/drivers/pmdomain/governor.c
> index c1e148657c873a6b5b4d9c0f058d54cb020c56e2..d5ac4c1b5b5a432f0072209d17379e58ec891202 100644
> --- a/drivers/pmdomain/governor.c
> +++ b/drivers/pmdomain/governor.c
> @@ -8,6 +8,7 @@
> #include <linux/pm_domain.h>
> #include <linux/pm_qos.h>
> #include <linux/hrtimer.h>
> +#include <linux/cpu.h>
> #include <linux/cpuidle.h>
> #include <linux/cpumask.h>
> #include <linux/ktime.h>
> @@ -349,6 +350,8 @@ static bool cpu_power_down_ok(struct dev_pm_domain *pd)
> struct cpuidle_device *dev;
> ktime_t domain_wakeup, next_hrtimer;
> ktime_t now = ktime_get();
> + struct device *device;
Nitpick: Maybe rename to "cpu_dev" to better distinguish between the
cpuidle_device *dev, above?
> + s64 cpu_constraint, global_constraint;
> s64 idle_duration_ns;
> int cpu, i;
>
> @@ -359,6 +362,7 @@ static bool cpu_power_down_ok(struct dev_pm_domain *pd)
> if (!(genpd->flags & GENPD_FLAG_CPU_DOMAIN))
> return true;
>
> + global_constraint = cpu_latency_qos_limit();
> /*
> * Find the next wakeup for any of the online CPUs within the PM domain
> * and its subdomains. Note, we only need the genpd->cpus, as it already
> @@ -372,8 +376,16 @@ static bool cpu_power_down_ok(struct dev_pm_domain *pd)
> if (ktime_before(next_hrtimer, domain_wakeup))
> domain_wakeup = next_hrtimer;
> }
> +
> + device = get_cpu_device(cpu);
> + if (device) {
> + cpu_constraint = dev_pm_qos_read_value(device, DEV_PM_QOS_RESUME_LATENCY);
We should be able to use dev_pm_qos_raw_resume_latency() here, similar
to how cpuidle_governor_latency_req() does it. I think it's better as
it avoids acquiring/releasing the spinlock.
> + if (cpu_constraint < global_constraint)
> + global_constraint = cpu_constraint;
> + }
> }
>
> + global_constraint *= NSEC_PER_USEC;
> /* The minimum idle duration is from now - until the next wakeup. */
> idle_duration_ns = ktime_to_ns(ktime_sub(domain_wakeup, now));
> if (idle_duration_ns <= 0)
> @@ -389,8 +401,10 @@ static bool cpu_power_down_ok(struct dev_pm_domain *pd)
> */
> i = genpd->state_idx;
> do {
> - if (idle_duration_ns >= (genpd->states[i].residency_ns +
> - genpd->states[i].power_off_latency_ns)) {
> + if ((idle_duration_ns >= (genpd->states[i].residency_ns +
> + genpd->states[i].power_off_latency_ns)) &&
> + (global_constraint >= (genpd->states[i].power_on_latency_ns +
> + genpd->states[i].power_off_latency_ns))) {
> genpd->state_idx = i;
> genpd->gd->last_enter = now;
> genpd->gd->reflect_residency = true;
>
> ---
> base-commit: 50c8770a42faf8b1c7abe93e7c114337f580a97d
> change-id: 20250703-pmdomain_qos-25b8dbb623ea
>
> Best regards,
> --
> Maulik Shah <maulik.shah@....qualcomm.com>
>
Besides the minor things above, this looks good to me.
Kind regards
Uffe
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