On Tue, Oct 20, 2020 at 8:05 PM 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
> residency requirements are not met.
>
> 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.
>
> Signed-off-by: Lina Iyer <ilina@xxxxxxxxxxxxxx>
A few nits follow.
> ---
> 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 | 84 ++++++++++++++++++++++++++--
> include/linux/pm_domain.h | 1 +
> 2 files changed, 80 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/base/power/domain_governor.c b/drivers/base/power/domain_governor.c
> index 490ed7deb99a..092927b60dc0 100644
> --- a/drivers/base/power/domain_governor.c
> +++ b/drivers/base/power/domain_governor.c
> @@ -117,6 +117,49 @@ 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;
> +
> + /* Find the earliest wakeup for all devices in the domain */
> + 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;
> + }
> +
> + /* Then find the earliest wakeup of from all the child domains */
> + 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;
> + }
This is assuming that the lists will remain stable during the walks
above, but is that guaranteed?
> +
> + genpd->next_wakeup = domain_wakeup;
> +}
> +
> +static bool next_wakeup_allows_state(struct generic_pm_domain *genpd,
> + unsigned int state, ktime_t now)
> +{
> + s64 idle_time_ns, min_sleep_ns;
> + ktime_t domain_wakeup = genpd->next_wakeup;
I'd move the second line to the top (it looks odd now IMO).
> +
> + min_sleep_ns = genpd->states[state].power_off_latency_ns +
> + genpd->states[state].power_on_latency_ns +
> + genpd->states[state].residency_ns;
> +
> + idle_time_ns = ktime_to_ns(ktime_sub(domain_wakeup, now));
> + if (idle_time_ns < min_sleep_ns)
> + return false;
> +
> + return true;
Why not
+ return idle_time_ns >= min_sleep_ns;
> +}
> +
> static bool __default_power_down_ok(struct dev_pm_domain *pd,
> unsigned int state)
> {
> @@ -210,6 +253,33 @@ static bool default_power_down_ok(struct dev_pm_domain *pd)
> {
> struct generic_pm_domain *genpd = pd_to_genpd(pd);
> struct gpd_link *link;
> + int state_idx;
Why not initialize it right away?
> + ktime_t now = ktime_get();
> +
> + /*
> + * 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);
> + state_idx = genpd->state_count - 1;
> + 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;
> @@ -228,17 +298,21 @@ 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;
> }
> diff --git a/include/linux/pm_domain.h b/include/linux/pm_domain.h
> index e00c77b1efd8..205b750a2e56 100644
> --- a/include/linux/pm_domain.h
> +++ b/include/linux/pm_domain.h
> @@ -130,6 +130,7 @@ 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;
> --
