We are providing headroom for the utilization to grow until the next
decision point to pick the next frequency. Give the function a better
name and give it some documentation. It is not really mapping anything.
Also move it to cpufreq_schedutil.c. This function relies on updating
util signal appropriately to give a headroom to grow. This is tied to
schedutil and scheduler and not something that can be shared with other
governors.
Acked-by: Viresh Kumar <[email protected]>
Acked-by: Rafael J. Wysocki <[email protected]>
Signed-off-by: Qais Yousef <[email protected]>
---
Changes in v2:
1. Add Acked-by from Viresh and Raphael (Thanks!)
2. Move the function to cpufreq_schedutil.c instead of sched.h
3. Name space the function with sugov_ to indicate it is special to
this governor only and not generic.
include/linux/sched/cpufreq.h | 5 -----
kernel/sched/cpufreq_schedutil.c | 20 +++++++++++++++++++-
2 files changed, 19 insertions(+), 6 deletions(-)
diff --git a/include/linux/sched/cpufreq.h b/include/linux/sched/cpufreq.h
index bdd31ab93bc5..d01755d3142f 100644
--- a/include/linux/sched/cpufreq.h
+++ b/include/linux/sched/cpufreq.h
@@ -28,11 +28,6 @@ static inline unsigned long map_util_freq(unsigned long util,
{
return freq * util / cap;
}
-
-static inline unsigned long map_util_perf(unsigned long util)
-{
- return util + (util >> 2);
-}
#endif /* CONFIG_CPU_FREQ */
#endif /* _LINUX_SCHED_CPUFREQ_H */
diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
index eece6244f9d2..575df3599813 100644
--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -178,12 +178,30 @@ static unsigned int get_next_freq(struct sugov_policy *sg_policy,
return cpufreq_driver_resolve_freq(policy, freq);
}
+/*
+ * DVFS decision are made at discrete points. If CPU stays busy, the util will
+ * continue to grow, which means it could need to run at a higher frequency
+ * before the next decision point was reached. IOW, we can't follow the util as
+ * it grows immediately, but there's a delay before we issue a request to go to
+ * higher frequency. The headroom caters for this delay so the system continues
+ * to run at adequate performance point.
+ *
+ * This function provides enough headroom to provide adequate performance
+ * assuming the CPU continues to be busy.
+ *
+ * At the moment it is a constant multiplication with 1.25.
+ */
+static inline unsigned long sugov_apply_dvfs_headroom(unsigned long util)
+{
+ return util + (util >> 2);
+}
+
unsigned long sugov_effective_cpu_perf(int cpu, unsigned long actual,
unsigned long min,
unsigned long max)
{
/* Add dvfs headroom to actual utilization */
- actual = map_util_perf(actual);
+ actual = sugov_apply_dvfs_headroom(actual);
/* Actually we don't need to target the max performance */
if (actual < max)
max = actual;
--
2.34.1
On Tue, 20 Feb 2024 at 19:08, Qais Yousef <[email protected]> wrote:
>
> We are providing headroom for the utilization to grow until the next
> decision point to pick the next frequency. Give the function a better
> name and give it some documentation. It is not really mapping anything.
>
> Also move it to cpufreq_schedutil.c. This function relies on updating
> util signal appropriately to give a headroom to grow. This is tied to
> schedutil and scheduler and not something that can be shared with other
> governors.
>
> Acked-by: Viresh Kumar <[email protected]>
> Acked-by: Rafael J. Wysocki <[email protected]>
> Signed-off-by: Qais Yousef <[email protected]>
Reviewed-by: Vincent Guittot <[email protected]>
> ---
>
> Changes in v2:
>
> 1. Add Acked-by from Viresh and Raphael (Thanks!)
> 2. Move the function to cpufreq_schedutil.c instead of sched.h
> 3. Name space the function with sugov_ to indicate it is special to
> this governor only and not generic.
>
> include/linux/sched/cpufreq.h | 5 -----
> kernel/sched/cpufreq_schedutil.c | 20 +++++++++++++++++++-
> 2 files changed, 19 insertions(+), 6 deletions(-)
>
> diff --git a/include/linux/sched/cpufreq.h b/include/linux/sched/cpufreq.h
> index bdd31ab93bc5..d01755d3142f 100644
> --- a/include/linux/sched/cpufreq.h
> +++ b/include/linux/sched/cpufreq.h
> @@ -28,11 +28,6 @@ static inline unsigned long map_util_freq(unsigned long util,
> {
> return freq * util / cap;
> }
> -
> -static inline unsigned long map_util_perf(unsigned long util)
> -{
> - return util + (util >> 2);
> -}
> #endif /* CONFIG_CPU_FREQ */
>
> #endif /* _LINUX_SCHED_CPUFREQ_H */
> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> index eece6244f9d2..575df3599813 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -178,12 +178,30 @@ static unsigned int get_next_freq(struct sugov_policy *sg_policy,
> return cpufreq_driver_resolve_freq(policy, freq);
> }
>
> +/*
> + * DVFS decision are made at discrete points. If CPU stays busy, the util will
> + * continue to grow, which means it could need to run at a higher frequency
> + * before the next decision point was reached. IOW, we can't follow the util as
> + * it grows immediately, but there's a delay before we issue a request to go to
> + * higher frequency. The headroom caters for this delay so the system continues
> + * to run at adequate performance point.
> + *
> + * This function provides enough headroom to provide adequate performance
> + * assuming the CPU continues to be busy.
> + *
> + * At the moment it is a constant multiplication with 1.25.
> + */
> +static inline unsigned long sugov_apply_dvfs_headroom(unsigned long util)
> +{
> + return util + (util >> 2);
> +}
> +
> unsigned long sugov_effective_cpu_perf(int cpu, unsigned long actual,
> unsigned long min,
> unsigned long max)
> {
> /* Add dvfs headroom to actual utilization */
> - actual = map_util_perf(actual);
> + actual = sugov_apply_dvfs_headroom(actual);
> /* Actually we don't need to target the max performance */
> if (actual < max)
> max = actual;
> --
> 2.34.1
>