On Mon, 30 Nov 2020 at 23:50, Lina Iyer <ilina@xxxxxxxxxxxxxx> wrote:
>
> Currently, a PM domain's idle state is determined based on whether the
> QoS requirements are met. This may not save power, if the idle state
/s/not save power/waste energy
/state/state's
> residency requirements are not met.
perhaps change to:
"minimum residency requirement can't be fulfilled."
>
> CPU PM domains use the next timer wakeup for the CPUs in the domain to
> determine the sleep duration of the domain. This is compared with the
> idle state residencies to determine the optimal idle state. For other PM
> domains, determining the sleep length is not that straight forward. But
> if the device's next_event is available, we can use that to determine
> the sleep duration of the PM domain.
>
> Let's update the domain governor logic to check for idle state residency
> based on the next wakeup of devices as well as QoS constraints.
I suggest to clarify that this is being done, only when the genpd has
the corresponding config bit/flag set, that was added in patch1.
>
> Signed-off-by: Lina Iyer <ilina@xxxxxxxxxxxxxx>
Other than the above (and potential updates needed from comments on
patch1 and patch2), this looks good to me!
Kind regards
Uffe
> ---
> Changes in v6:
> - Do not include power_on_latency_ns for next_wakeup
> determination.
> - Re-organize code to avoid multiple ktime_get() reads.
> - Check genpd flag if next_wakeup is useful for the domain.
> - Document why we ignore stale data
> Changes in v5:
> - Minor code changes suggested by Rafel
> Changes in v4:
> - Update to use next_wakeup from struct generic_pm_domain_data.
> Changes in v3:
> - None
> Changes in v2:
> - Fix state_idx type to hold negative value.
> - Update commit text.
> ---
> drivers/base/power/domain_governor.c | 102 ++++++++++++++++++++++++---
> include/linux/pm_domain.h | 1 +
> 2 files changed, 94 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/base/power/domain_governor.c b/drivers/base/power/domain_governor.c
> index 490ed7deb99a..2afb7fa90d5d 100644
> --- a/drivers/base/power/domain_governor.c
> +++ b/drivers/base/power/domain_governor.c
> @@ -117,6 +117,55 @@ static bool default_suspend_ok(struct device *dev)
> return td->cached_suspend_ok;
> }
>
> +static void update_domain_next_wakeup(struct generic_pm_domain *genpd, ktime_t now)
> +{
> + ktime_t domain_wakeup = KTIME_MAX;
> + ktime_t next_wakeup;
> + struct pm_domain_data *pdd;
> + struct gpd_link *link;
> +
> + if (!genpd_may_use_next_wakeup(genpd))
> + return;
> +
> + /*
> + * Devices that have a predictable wakeup pattern, may specify
> + * their next wakeup. Let's find the next wakeup from all the
> + * devices attached to this domain and from all the sub-domains.
> + * It is possible that component's a next wakeup may have become
> + * stale when we read that here. We will ignore to ensure the domain
> + * is able to enter its optimal idle state.
> + */
> + list_for_each_entry(pdd, &genpd->dev_list, list_node) {
> + next_wakeup = to_gpd_data(pdd)->next_wakeup;
> + if (next_wakeup != KTIME_MAX && !ktime_before(next_wakeup, now))
> + if (ktime_before(next_wakeup, domain_wakeup))
> + domain_wakeup = next_wakeup;
> + }
> +
> + list_for_each_entry(link, &genpd->parent_links, parent_node) {
> + next_wakeup = link->child->next_wakeup;
> + if (next_wakeup != KTIME_MAX && !ktime_before(next_wakeup, now))
> + if (ktime_before(next_wakeup, domain_wakeup))
> + domain_wakeup = next_wakeup;
> + }
> +
> + genpd->next_wakeup = domain_wakeup;
> +}
> +
> +static bool next_wakeup_allows_state(struct generic_pm_domain *genpd,
> + unsigned int state, ktime_t now)
> +{
> + ktime_t domain_wakeup = genpd->next_wakeup;
> + s64 idle_time_ns, min_sleep_ns;
> +
> + min_sleep_ns = genpd->states[state].power_off_latency_ns +
> + genpd->states[state].residency_ns;
> +
> + idle_time_ns = ktime_to_ns(ktime_sub(domain_wakeup, now));
> +
> + return idle_time_ns >= min_sleep_ns;
> +}
> +
> static bool __default_power_down_ok(struct dev_pm_domain *pd,
> unsigned int state)
> {
> @@ -201,16 +250,41 @@ static bool __default_power_down_ok(struct dev_pm_domain *pd,
> }
>
> /**
> - * default_power_down_ok - Default generic PM domain power off governor routine.
> + * _default_power_down_ok - Default generic PM domain power off governor routine.
> * @pd: PM domain to check.
> *
> * This routine must be executed under the PM domain's lock.
> */
> -static bool default_power_down_ok(struct dev_pm_domain *pd)
> +static bool _default_power_down_ok(struct dev_pm_domain *pd, ktime_t now)
> {
> struct generic_pm_domain *genpd = pd_to_genpd(pd);
> + int state_idx = genpd->state_count - 1;
> struct gpd_link *link;
>
> + /*
> + * Find the next wakeup from devices that can determine their own wakeup
> + * to find when the domain would wakeup and do it for every device down
> + * the hierarchy. It is not worth while to sleep if the state's residency
> + * cannot be met.
> + */
> + update_domain_next_wakeup(genpd, now);
> + if (genpd->next_wakeup != KTIME_MAX) {
> + /* Let's find out the deepest domain idle state, the devices prefer */
> + while (state_idx >= 0) {
> + if (next_wakeup_allows_state(genpd, state_idx, now)) {
> + genpd->max_off_time_changed = true;
> + break;
> + }
> + state_idx--;
> + }
> +
> + if (state_idx < 0) {
> + state_idx = 0;
> + genpd->cached_power_down_ok = false;
> + goto done;
> + }
> + }
> +
> if (!genpd->max_off_time_changed) {
> genpd->state_idx = genpd->cached_power_down_state_idx;
> return genpd->cached_power_down_ok;
> @@ -228,21 +302,30 @@ static bool default_power_down_ok(struct dev_pm_domain *pd)
> genpd->max_off_time_ns = -1;
> genpd->max_off_time_changed = false;
> genpd->cached_power_down_ok = true;
> - genpd->state_idx = genpd->state_count - 1;
>
> - /* Find a state to power down to, starting from the deepest. */
> - while (!__default_power_down_ok(pd, genpd->state_idx)) {
> - if (genpd->state_idx == 0) {
> + /*
> + * Find a state to power down to, starting from the state
> + * determined by the next wakeup.
> + */
> + while (!__default_power_down_ok(pd, state_idx)) {
> + if (state_idx == 0) {
> genpd->cached_power_down_ok = false;
> break;
> }
> - genpd->state_idx--;
> + state_idx--;
> }
>
> +done:
> + genpd->state_idx = state_idx;
> genpd->cached_power_down_state_idx = genpd->state_idx;
> return genpd->cached_power_down_ok;
> }
>
> +static bool default_power_down_ok(struct dev_pm_domain *pd)
> +{
> + return _default_power_down_ok(pd, ktime_get());
> +}
> +
> static bool always_on_power_down_ok(struct dev_pm_domain *domain)
> {
> return false;
> @@ -254,11 +337,12 @@ static bool cpu_power_down_ok(struct dev_pm_domain *pd)
> struct generic_pm_domain *genpd = pd_to_genpd(pd);
> struct cpuidle_device *dev;
> ktime_t domain_wakeup, next_hrtimer;
> + ktime_t now = ktime_get();
> s64 idle_duration_ns;
> int cpu, i;
>
> /* Validate dev PM QoS constraints. */
> - if (!default_power_down_ok(pd))
> + if (!_default_power_down_ok(pd, now))
> return false;
>
> if (!(genpd->flags & GENPD_FLAG_CPU_DOMAIN))
> @@ -280,7 +364,7 @@ static bool cpu_power_down_ok(struct dev_pm_domain *pd)
> }
>
> /* The minimum idle duration is from now - until the next wakeup. */
> - idle_duration_ns = ktime_to_ns(ktime_sub(domain_wakeup, ktime_get()));
> + idle_duration_ns = ktime_to_ns(ktime_sub(domain_wakeup, now));
> if (idle_duration_ns <= 0)
> return false;
>
> diff --git a/include/linux/pm_domain.h b/include/linux/pm_domain.h
> index cc27d3d88849..a41aea9d1c06 100644
> --- a/include/linux/pm_domain.h
> +++ b/include/linux/pm_domain.h
> @@ -136,6 +136,7 @@ struct generic_pm_domain {
> unsigned int state);
> struct gpd_dev_ops dev_ops;
> s64 max_off_time_ns; /* Maximum allowed "suspended" time. */
> + ktime_t next_wakeup; /* Maintained by the domain governor */
> bool max_off_time_changed;
> bool cached_power_down_ok;
> bool cached_power_down_state_idx;
> --
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> a Linux Foundation Collaborative Project
>
