| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <CAPDyKFpq_mkyGfR-OYwTU3k62fkzXWiz07ZSR5j+FY72vYXxmQ@mail.gmail.com>
Date: Mon, 2 Feb 2026 12:49:05 +0100
From: Ulf Hansson <ulf.hansson@...aro.org>
To: "Kevin Hilman (TI)" <khilman@...libre.com>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, linux-pm@...r.kernel.org,
Dhruva Gole <d-gole@...com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] pmdommain: add support system-wide resume latency constraints
On Wed, 21 Jan 2026 at 02:54, Kevin Hilman (TI) <khilman@...libre.com> wrote:
>
> In addition to checking for CPU latency constraints when checking if
> OK to power down a domain, also check for QoS latency constraints in
> all devices of a domain and use that in determining the final latency
> constraint to use for the domain.
>
> Since cpu_system_power_down_ok() is used for system-wide suspend, the
> per-device constratints are only relevant if the LATENCY_SYS QoS flag
> is set.
>
> Because this flag implies the latency constraint only applies to
> system-wide suspend, also check the flag in
> dev_update_qos_constraint(). If it is set, then the constraint is not
> relevant for runtime PM decisions.
>
> Signed-off-by: Kevin Hilman (TI) <khilman@...libre.com>
> ---
> drivers/pmdomain/governor.c | 42 +++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 41 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/pmdomain/governor.c b/drivers/pmdomain/governor.c
> index 96737abbb496..03802a859a78 100644
> --- a/drivers/pmdomain/governor.c
> +++ b/drivers/pmdomain/governor.c
> @@ -31,6 +31,8 @@ static int dev_update_qos_constraint(struct device *dev, void *data)
> constraint_ns = td ? td->effective_constraint_ns :
> PM_QOS_RESUME_LATENCY_NO_CONSTRAINT_NS;
> } else {
> + enum pm_qos_flags_status flag_status;
> +
> /*
> * The child is not in a domain and there's no info on its
> * suspend/resume latencies, so assume them to be negligible and
> @@ -38,7 +40,14 @@ static int dev_update_qos_constraint(struct device *dev, void *data)
> * known at this point anyway).
> */
> constraint_ns = dev_pm_qos_read_value(dev, DEV_PM_QOS_RESUME_LATENCY);
> - constraint_ns *= NSEC_PER_USEC;
> + flag_status = dev_pm_qos_flags(dev, PM_QOS_FLAG_LATENCY_SYS);
> + if ((constraint_ns != PM_QOS_RESUME_LATENCY_NO_CONSTRAINT) &&
> + (flag_status == PM_QOS_FLAGS_ALL)) {
> + dev_dbg_once(dev, "resume-latency only for system-wide. Ignoring.\n");
> + constraint_ns = PM_QOS_RESUME_LATENCY_NO_CONSTRAINT_NS;
> + } else {
> + constraint_ns *= NSEC_PER_USEC;
> + }
> }
dev_update_qos_constraint() is called only to take into account the
QoS constraints for the device's *children*.
It looks like we should also be checking the PM_QOS_FLAG_LATENCY_SYS
flag in default_suspend_ok() for the device in question.
That said, there seems to be more places in the kernel where we should
check the PM_QOS_FLAG_LATENCY_SYS flag, like in cpu_power_down_ok(),
cpuidle_governor_latency_req(), etc.
>
> if (constraint_ns < *constraint_ns_p)
> @@ -430,12 +439,43 @@ static bool cpu_system_power_down_ok(struct dev_pm_domain *pd)
> s64 constraint_ns = cpu_wakeup_latency_qos_limit() * NSEC_PER_USEC;
> struct generic_pm_domain *genpd = pd_to_genpd(pd);
> int state_idx = genpd->state_count - 1;
> + struct pm_domain_data *pdd;
> + s32 min_dev_latency = PM_QOS_RESUME_LATENCY_NO_CONSTRAINT;
> + s64 min_dev_latency_ns = PM_QOS_RESUME_LATENCY_NO_CONSTRAINT_NS;
> + struct gpd_link *link;
>
> if (!(genpd->flags & GENPD_FLAG_CPU_DOMAIN)) {
> genpd->state_idx = state_idx;
> return true;
> }
>
> + list_for_each_entry(link, &genpd->parent_links, parent_node) {
> + struct generic_pm_domain *child_pd = link->child;
> +
> + list_for_each_entry(pdd, &child_pd->dev_list, list_node) {
> + enum pm_qos_flags_status flag_status;
> + s32 dev_latency;
> +
> + dev_latency = dev_pm_qos_read_value(pdd->dev, DEV_PM_QOS_RESUME_LATENCY);
> + flag_status = dev_pm_qos_flags(pdd->dev, PM_QOS_FLAG_LATENCY_SYS);
> + if ((dev_latency != PM_QOS_RESUME_LATENCY_NO_CONSTRAINT) &&
> + (flag_status == PM_QOS_FLAGS_ALL)) {
> + dev_dbg(pdd->dev,
> + "in domain %s, has QoS system-wide resume latency=%d\n",
> + child_pd->name, dev_latency);
> + if (dev_latency < min_dev_latency)
> + min_dev_latency = dev_latency;
> + }
> + }
cpu_system_power_down_ok() is at the moment only used for CPU PM
domains. If the intent is to take into account QoS constraints for
CPUs, we should check the QoS value for CPU-devices as well (by using
get_cpu_device(), see cpu_power_down_ok(). For non-CPU devices
something along the lines of the above makes sense to me.
Although, please note, the above code is just walking through the
devices in the child-domains, there is nothing checking the devices
that belong to the current/parent-domain. Nor are we taking
child-devices into account.
> + }
> +
> + /* If device latency < CPU wakeup latency, use it instead */
> + if (min_dev_latency != PM_QOS_RESUME_LATENCY_NO_CONSTRAINT) {
> + min_dev_latency_ns = min_dev_latency * NSEC_PER_USEC;
> + if (min_dev_latency_ns < constraint_ns)
> + constraint_ns = min_dev_latency_ns;
> + }
> +
> /* Find the deepest state for the latency constraint. */
> while (state_idx >= 0) {
> s64 latency_ns = genpd->states[state_idx].power_off_latency_ns +
>
> --
> 2.51.0
>
Kind regards
Uffe
Powered by blists - more mailing lists