When uclamp_max is being used, the util of the task could be higher than
the spare capacity of the CPU, but due to uclamp_max value we force fit
it there.
The way the condition for checking for max_spare_cap in
find_energy_efficient_cpu() was constructed; it ignored any CPU that has
its spare_cap less than or _equal_ to max_spare_cap. Since we initialize
max_spare_cap to 0; this lead to never setting max_spare_cap_cpu and
hence ending up never performing compute_energy() for this cluster and
missing an opportunity for a better energy efficient placement to honour
uclamp_max setting.
max_spare_cap = 0;
cpu_cap = capacity_of(cpu) - task_util(p); // 0 if task_util(p) is high
...
util_fits_cpu(...); // will return true if uclamp_max forces it to fit
...
// this logic will fail to update max_spare_cap_cpu if cpu_cap is 0
if (cpu_cap > max_spare_cap) {
max_spare_cap = cpu_cap;
max_spare_cap_cpu = cpu;
}
prev_spare_cap suffers from a similar problem.
Fix the logic by treating -1UL value as 'not populated' instead of
0 which is a viable and correct spare capacity value.
Fixes: 1d42509e475c ("sched/fair: Make EAS wakeup placement consider uclamp restrictions")
Signed-off-by: Qais Yousef (Google) <qyousef@layalina.io>
---
kernel/sched/fair.c | 14 ++++++++------
1 file changed, 8 insertions(+), 6 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index e29e9ea4cde8..ca2c389d3180 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7390,9 +7390,9 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
for (; pd; pd = pd->next) {
unsigned long util_min = p_util_min, util_max = p_util_max;
unsigned long cpu_cap, cpu_thermal_cap, util;
- unsigned long cur_delta, max_spare_cap = 0;
+ unsigned long cur_delta, max_spare_cap = -1UL;
unsigned long rq_util_min, rq_util_max;
- unsigned long prev_spare_cap = 0;
+ unsigned long prev_spare_cap = -1UL;
int max_spare_cap_cpu = -1;
unsigned long base_energy;
int fits, max_fits = -1;
@@ -7457,7 +7457,8 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
prev_spare_cap = cpu_cap;
prev_fits = fits;
} else if ((fits > max_fits) ||
- ((fits == max_fits) && (cpu_cap > max_spare_cap))) {
+ ((fits == max_fits) &&
+ (cpu_cap > max_spare_cap || max_spare_cap == -1UL) {
/*
* Find the CPU with the maximum spare capacity
* among the remaining CPUs in the performance
@@ -7469,7 +7470,7 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
}
}
- if (max_spare_cap_cpu < 0 && prev_spare_cap == 0)
+ if (max_spare_cap_cpu < 0 && prev_spare_cap == -1UL)
continue;
eenv_pd_busy_time(&eenv, cpus, p);
@@ -7477,7 +7478,7 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
base_energy = compute_energy(&eenv, pd, cpus, p, -1);
/* Evaluate the energy impact of using prev_cpu. */
- if (prev_spare_cap > 0) {
+ if (prev_spare_cap != -1UL) {
prev_delta = compute_energy(&eenv, pd, cpus, p,
prev_cpu);
/* CPU utilization has changed */
@@ -7489,7 +7490,8 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
}
/* Evaluate the energy impact of using max_spare_cap_cpu. */
- if (max_spare_cap_cpu >= 0 && max_spare_cap > prev_spare_cap) {
+ if (max_spare_cap_cpu >= 0 &&
+ (max_spare_cap > prev_spare_cap || prev_spare_cap == -1UL)) {
/* Current best energy cpu fits better */
if (max_fits < best_fits)
continue;
--
2.25.1On Sun, 29 Jan 2023 at 17:14, Qais Yousef <qyousef@layalina.io> wrote:
>
> When uclamp_max is being used, the util of the task could be higher than
> the spare capacity of the CPU, but due to uclamp_max value we force fit
> it there.
>
> The way the condition for checking for max_spare_cap in
> find_energy_efficient_cpu() was constructed; it ignored any CPU that has
> its spare_cap less than or _equal_ to max_spare_cap. Since we initialize
> max_spare_cap to 0; this lead to never setting max_spare_cap_cpu and
> hence ending up never performing compute_energy() for this cluster and
> missing an opportunity for a better energy efficient placement to honour
> uclamp_max setting.
>
> max_spare_cap = 0;
> cpu_cap = capacity_of(cpu) - task_util(p); // 0 if task_util(p) is high
>
> ...
>
> util_fits_cpu(...); // will return true if uclamp_max forces it to fit
>
> ...
>
> // this logic will fail to update max_spare_cap_cpu if cpu_cap is 0
> if (cpu_cap > max_spare_cap) {
> max_spare_cap = cpu_cap;
> max_spare_cap_cpu = cpu;
> }
>
> prev_spare_cap suffers from a similar problem.
>
> Fix the logic by treating -1UL value as 'not populated' instead of
> 0 which is a viable and correct spare capacity value.
>
> Fixes: 1d42509e475c ("sched/fair: Make EAS wakeup placement consider uclamp restrictions")
> Signed-off-by: Qais Yousef (Google) <qyousef@layalina.io>
> ---
> kernel/sched/fair.c | 14 ++++++++------
> 1 file changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index e29e9ea4cde8..ca2c389d3180 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -7390,9 +7390,9 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
> for (; pd; pd = pd->next) {
> unsigned long util_min = p_util_min, util_max = p_util_max;
> unsigned long cpu_cap, cpu_thermal_cap, util;
> - unsigned long cur_delta, max_spare_cap = 0;
> + unsigned long cur_delta, max_spare_cap = -1UL;
> unsigned long rq_util_min, rq_util_max;
> - unsigned long prev_spare_cap = 0;
> + unsigned long prev_spare_cap = -1UL;
> int max_spare_cap_cpu = -1;
> unsigned long base_energy;
> int fits, max_fits = -1;
> @@ -7457,7 +7457,8 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
> prev_spare_cap = cpu_cap;
> prev_fits = fits;
> } else if ((fits > max_fits) ||
> - ((fits == max_fits) && (cpu_cap > max_spare_cap))) {
> + ((fits == max_fits) &&
> + (cpu_cap > max_spare_cap || max_spare_cap == -1UL) {
Can't we use a signed comparison to include the case of max_spare_cap
== -1 in cpu_cap > max_spare_cap ?
> /*
> * Find the CPU with the maximum spare capacity
> * among the remaining CPUs in the performance
> @@ -7469,7 +7470,7 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
> }
> }
>
> - if (max_spare_cap_cpu < 0 && prev_spare_cap == 0)
> + if (max_spare_cap_cpu < 0 && prev_spare_cap == -1UL)
> continue;
>
> eenv_pd_busy_time(&eenv, cpus, p);
> @@ -7477,7 +7478,7 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
> base_energy = compute_energy(&eenv, pd, cpus, p, -1);
>
> /* Evaluate the energy impact of using prev_cpu. */
> - if (prev_spare_cap > 0) {
> + if (prev_spare_cap != -1UL) {
> prev_delta = compute_energy(&eenv, pd, cpus, p,
> prev_cpu);
> /* CPU utilization has changed */
> @@ -7489,7 +7490,8 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
> }
>
> /* Evaluate the energy impact of using max_spare_cap_cpu. */
> - if (max_spare_cap_cpu >= 0 && max_spare_cap > prev_spare_cap) {
> + if (max_spare_cap_cpu >= 0 &&
> + (max_spare_cap > prev_spare_cap || prev_spare_cap == -1UL)) {
> /* Current best energy cpu fits better */
> if (max_fits < best_fits)
> continue;
> --
> 2.25.1
>
On 01/30/23 15:44, Vincent Guittot wrote:
> On Sun, 29 Jan 2023 at 17:14, Qais Yousef <qyousef@layalina.io> wrote:
> >
> > When uclamp_max is being used, the util of the task could be higher than
> > the spare capacity of the CPU, but due to uclamp_max value we force fit
> > it there.
> >
> > The way the condition for checking for max_spare_cap in
> > find_energy_efficient_cpu() was constructed; it ignored any CPU that has
> > its spare_cap less than or _equal_ to max_spare_cap. Since we initialize
> > max_spare_cap to 0; this lead to never setting max_spare_cap_cpu and
> > hence ending up never performing compute_energy() for this cluster and
> > missing an opportunity for a better energy efficient placement to honour
> > uclamp_max setting.
> >
> > max_spare_cap = 0;
> > cpu_cap = capacity_of(cpu) - task_util(p); // 0 if task_util(p) is high
> >
> > ...
> >
> > util_fits_cpu(...); // will return true if uclamp_max forces it to fit
> >
> > ...
> >
> > // this logic will fail to update max_spare_cap_cpu if cpu_cap is 0
> > if (cpu_cap > max_spare_cap) {
> > max_spare_cap = cpu_cap;
> > max_spare_cap_cpu = cpu;
> > }
> >
> > prev_spare_cap suffers from a similar problem.
> >
> > Fix the logic by treating -1UL value as 'not populated' instead of
> > 0 which is a viable and correct spare capacity value.
> >
> > Fixes: 1d42509e475c ("sched/fair: Make EAS wakeup placement consider uclamp restrictions")
> > Signed-off-by: Qais Yousef (Google) <qyousef@layalina.io>
> > ---
> > kernel/sched/fair.c | 14 ++++++++------
> > 1 file changed, 8 insertions(+), 6 deletions(-)
> >
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index e29e9ea4cde8..ca2c389d3180 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -7390,9 +7390,9 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
> > for (; pd; pd = pd->next) {
> > unsigned long util_min = p_util_min, util_max = p_util_max;
> > unsigned long cpu_cap, cpu_thermal_cap, util;
> > - unsigned long cur_delta, max_spare_cap = 0;
> > + unsigned long cur_delta, max_spare_cap = -1UL;
> > unsigned long rq_util_min, rq_util_max;
> > - unsigned long prev_spare_cap = 0;
> > + unsigned long prev_spare_cap = -1UL;
> > int max_spare_cap_cpu = -1;
> > unsigned long base_energy;
> > int fits, max_fits = -1;
> > @@ -7457,7 +7457,8 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
> > prev_spare_cap = cpu_cap;
> > prev_fits = fits;
> > } else if ((fits > max_fits) ||
> > - ((fits == max_fits) && (cpu_cap > max_spare_cap))) {
> > + ((fits == max_fits) &&
> > + (cpu_cap > max_spare_cap || max_spare_cap == -1UL) {
>
> Can't we use a signed comparison to include the case of max_spare_cap
> == -1 in cpu_cap > max_spare_cap ?
By converting max_spare_cap to long, right?
My memory could be failing me, but I seem to remember we had mixed usage and
consolidated into unsigned long. That's why I didn't want to break the trend.
Anyway. If no one shouts against that, I don't mind going for that.
Thanks
--
Qais Yousef
>
> > /*
> > * Find the CPU with the maximum spare capacity
> > * among the remaining CPUs in the performance
> > @@ -7469,7 +7470,7 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
> > }
> > }
> >
> > - if (max_spare_cap_cpu < 0 && prev_spare_cap == 0)
> > + if (max_spare_cap_cpu < 0 && prev_spare_cap == -1UL)
> > continue;
> >
> > eenv_pd_busy_time(&eenv, cpus, p);
> > @@ -7477,7 +7478,7 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
> > base_energy = compute_energy(&eenv, pd, cpus, p, -1);
> >
> > /* Evaluate the energy impact of using prev_cpu. */
> > - if (prev_spare_cap > 0) {
> > + if (prev_spare_cap != -1UL) {
> > prev_delta = compute_energy(&eenv, pd, cpus, p,
> > prev_cpu);
> > /* CPU utilization has changed */
> > @@ -7489,7 +7490,8 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
> > }
> >
> > /* Evaluate the energy impact of using max_spare_cap_cpu. */
> > - if (max_spare_cap_cpu >= 0 && max_spare_cap > prev_spare_cap) {
> > + if (max_spare_cap_cpu >= 0 &&
> > + (max_spare_cap > prev_spare_cap || prev_spare_cap == -1UL)) {
> > /* Current best energy cpu fits better */
> > if (max_fits < best_fits)
> > continue;
> > --
> > 2.25.1
> >
On 01/29/23 16:14, Qais Yousef wrote:
> When uclamp_max is being used, the util of the task could be higher than
> the spare capacity of the CPU, but due to uclamp_max value we force fit
> it there.
>
> The way the condition for checking for max_spare_cap in
> find_energy_efficient_cpu() was constructed; it ignored any CPU that has
> its spare_cap less than or _equal_ to max_spare_cap. Since we initialize
> max_spare_cap to 0; this lead to never setting max_spare_cap_cpu and
> hence ending up never performing compute_energy() for this cluster and
> missing an opportunity for a better energy efficient placement to honour
> uclamp_max setting.
>
> max_spare_cap = 0;
> cpu_cap = capacity_of(cpu) - task_util(p); // 0 if task_util(p) is high
>
> ...
>
> util_fits_cpu(...); // will return true if uclamp_max forces it to fit
>
> ...
>
> // this logic will fail to update max_spare_cap_cpu if cpu_cap is 0
> if (cpu_cap > max_spare_cap) {
> max_spare_cap = cpu_cap;
> max_spare_cap_cpu = cpu;
> }
>
> prev_spare_cap suffers from a similar problem.
>
> Fix the logic by treating -1UL value as 'not populated' instead of
> 0 which is a viable and correct spare capacity value.
>
> Fixes: 1d42509e475c ("sched/fair: Make EAS wakeup placement consider uclamp restrictions")
> Signed-off-by: Qais Yousef (Google) <qyousef@layalina.io>
> ---
> kernel/sched/fair.c | 14 ++++++++------
> 1 file changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index e29e9ea4cde8..ca2c389d3180 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -7390,9 +7390,9 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
> for (; pd; pd = pd->next) {
> unsigned long util_min = p_util_min, util_max = p_util_max;
> unsigned long cpu_cap, cpu_thermal_cap, util;
> - unsigned long cur_delta, max_spare_cap = 0;
> + unsigned long cur_delta, max_spare_cap = -1UL;
> unsigned long rq_util_min, rq_util_max;
> - unsigned long prev_spare_cap = 0;
> + unsigned long prev_spare_cap = -1UL;
> int max_spare_cap_cpu = -1;
> unsigned long base_energy;
> int fits, max_fits = -1;
> @@ -7457,7 +7457,8 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
> prev_spare_cap = cpu_cap;
> prev_fits = fits;
> } else if ((fits > max_fits) ||
> - ((fits == max_fits) && (cpu_cap > max_spare_cap))) {
> + ((fits == max_fits) &&
> + (cpu_cap > max_spare_cap || max_spare_cap == -1UL) {
Oops. Sorry I just realized I bodged this while rebasing and preparing the
patches for posting. There are missing termination parenthesis that will cause
compilation errors.
Apologies..
--
Qais Yousef
> /*
> * Find the CPU with the maximum spare capacity
> * among the remaining CPUs in the performance
> @@ -7469,7 +7470,7 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
> }
> }
>
> - if (max_spare_cap_cpu < 0 && prev_spare_cap == 0)
> + if (max_spare_cap_cpu < 0 && prev_spare_cap == -1UL)
> continue;
>
> eenv_pd_busy_time(&eenv, cpus, p);
> @@ -7477,7 +7478,7 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
> base_energy = compute_energy(&eenv, pd, cpus, p, -1);
>
> /* Evaluate the energy impact of using prev_cpu. */
> - if (prev_spare_cap > 0) {
> + if (prev_spare_cap != -1UL) {
> prev_delta = compute_energy(&eenv, pd, cpus, p,
> prev_cpu);
> /* CPU utilization has changed */
> @@ -7489,7 +7490,8 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
> }
>
> /* Evaluate the energy impact of using max_spare_cap_cpu. */
> - if (max_spare_cap_cpu >= 0 && max_spare_cap > prev_spare_cap) {
> + if (max_spare_cap_cpu >= 0 &&
> + (max_spare_cap > prev_spare_cap || prev_spare_cap == -1UL)) {
> /* Current best energy cpu fits better */
> if (max_fits < best_fits)
> continue;
> --
> 2.25.1
>
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