kernel/power/energy_model.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
From: Yaxiong Tian <tianyaxiong@kylinos.cn>
When the device is of a non-CPU type, table[i].performance won't be
initialized in the previous em_init_performance(), resulting in division
by zero when calculating costs in em_compute_costs().
Since the 'cost' algorithm is only used for EAS energy efficiency
calculations and is currently not utilized by other device drivers, we
should add the _is_cpu_device(dev) check to prevent this division-by-zero
issue.
Fixes: <1b600da51073> ("PM: EM: Optimize em_cpu_energy() and remove division")
Signed-off-by: Yaxiong Tian <tianyaxiong@kylinos.cn>
---
kernel/power/energy_model.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/power/energy_model.c b/kernel/power/energy_model.c
index d9b7e2b38c7a..fc972cc1fc12 100644
--- a/kernel/power/energy_model.c
+++ b/kernel/power/energy_model.c
@@ -235,7 +235,7 @@ static int em_compute_costs(struct device *dev, struct em_perf_state *table,
/* Compute the cost of each performance state. */
for (i = nr_states - 1; i >= 0; i--) {
- unsigned long power_res, cost;
+ unsigned long power_res, cost = 0;
if ((flags & EM_PERF_DOMAIN_ARTIFICIAL) && cb->get_cost) {
ret = cb->get_cost(dev, table[i].frequency, &cost);
@@ -244,7 +244,7 @@ static int em_compute_costs(struct device *dev, struct em_perf_state *table,
cost, ret);
return -EINVAL;
}
- } else {
+ } else if (_is_cpu_device(dev)) {
/* increase resolution of 'cost' precision */
power_res = table[i].power * 10;
cost = power_res / table[i].performance;
--
2.25.1On Mon, Apr 14, 2025 at 11:09 AM Yaxiong Tian <iambestgod@qq.com> wrote:
>
> From: Yaxiong Tian <tianyaxiong@kylinos.cn>
>
> When the device is of a non-CPU type, table[i].performance won't be
> initialized in the previous em_init_performance(), resulting in division
> by zero when calculating costs in em_compute_costs().
>
> Since the 'cost' algorithm is only used for EAS energy efficiency
> calculations and is currently not utilized by other device drivers, we
> should add the _is_cpu_device(dev) check to prevent this division-by-zero
> issue.
>
> Fixes: <1b600da51073> ("PM: EM: Optimize em_cpu_energy() and remove division")
Please look at the Fixes: tags in the kernel git history. They don't
look like the one above.
> Signed-off-by: Yaxiong Tian <tianyaxiong@kylinos.cn>
> ---
> kernel/power/energy_model.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/power/energy_model.c b/kernel/power/energy_model.c
> index d9b7e2b38c7a..fc972cc1fc12 100644
> --- a/kernel/power/energy_model.c
> +++ b/kernel/power/energy_model.c
> @@ -235,7 +235,7 @@ static int em_compute_costs(struct device *dev, struct em_perf_state *table,
>
> /* Compute the cost of each performance state. */
> for (i = nr_states - 1; i >= 0; i--) {
> - unsigned long power_res, cost;
> + unsigned long power_res, cost = 0;
>
> if ((flags & EM_PERF_DOMAIN_ARTIFICIAL) && cb->get_cost) {
> ret = cb->get_cost(dev, table[i].frequency, &cost);
> @@ -244,7 +244,7 @@ static int em_compute_costs(struct device *dev, struct em_perf_state *table,
> cost, ret);
> return -EINVAL;
> }
> - } else {
> + } else if (_is_cpu_device(dev)) {
Can't you just check this upfront at the beginning of the function and
make it bail out if dev is not a CPU device?
> /* increase resolution of 'cost' precision */
> power_res = table[i].power * 10;
> cost = power_res / table[i].performance;
> --
在 2025/4/16 01:17, Rafael J. Wysocki 写道:
> On Mon, Apr 14, 2025 at 11:09 AM Yaxiong Tian <iambestgod@qq.com> wrote:
>>
>> From: Yaxiong Tian <tianyaxiong@kylinos.cn>
>>
>> When the device is of a non-CPU type, table[i].performance won't be
>> initialized in the previous em_init_performance(), resulting in division
>> by zero when calculating costs in em_compute_costs().
>>
>> Since the 'cost' algorithm is only used for EAS energy efficiency
>> calculations and is currently not utilized by other device drivers, we
>> should add the _is_cpu_device(dev) check to prevent this division-by-zero
>> issue.
>>
>> Fixes: <1b600da51073> ("PM: EM: Optimize em_cpu_energy() and remove division")
>
> Please look at the Fixes: tags in the kernel git history. They don't
> look like the one above.
>
Yes, there's an extra '<>' here.
>> Signed-off-by: Yaxiong Tian <tianyaxiong@kylinos.cn>
>> ---
>> kernel/power/energy_model.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/kernel/power/energy_model.c b/kernel/power/energy_model.c
>> index d9b7e2b38c7a..fc972cc1fc12 100644
>> --- a/kernel/power/energy_model.c
>> +++ b/kernel/power/energy_model.c
>> @@ -235,7 +235,7 @@ static int em_compute_costs(struct device *dev, struct em_perf_state *table,
>>
>> /* Compute the cost of each performance state. */
>> for (i = nr_states - 1; i >= 0; i--) {
>> - unsigned long power_res, cost;
>> + unsigned long power_res, cost = 0;
>>
>> if ((flags & EM_PERF_DOMAIN_ARTIFICIAL) && cb->get_cost) {
>> ret = cb->get_cost(dev, table[i].frequency, &cost);
>> @@ -244,7 +244,7 @@ static int em_compute_costs(struct device *dev, struct em_perf_state *table,
>> cost, ret);
>> return -EINVAL;
>> }
>> - } else {
>> + } else if (_is_cpu_device(dev)) {
>
> Can't you just check this upfront at the beginning of the function and
> make it bail out if dev is not a CPU device?
>
Sure, But the current implementation applies em_compute_costs() to both
non-CPU devices and CPU devices. After carefully reviewing the latest code,
I've found this issue has expanded in scope.
There are currently three call paths for invoking em_compute_costs():
1) Registering performance domains (for both non-CPU and CPU devices)
em_dev_register_perf_domain() → em_create_pd() →
em_create_perf_table() → em_compute_costs()
2)EM update paths (CPU devices only)
Periodic 1000ms update check via em_update_work work item:
em_check_capacity_update() → em_adjust_new_capacity() →
em_recalc_and_update() → em_compute_costs()
Exynos-chip initialization:
em_dev_update_chip_binning() → em_recalc_and_update() → em_compute_costs()
3) Device cost computation (non-CPU devices only - currently unused)
em_dev_compute_costs() → em_compute_costs()
Note: In em_dev_compute_costs(), when calling em_compute_costs(),
neither the callback (cb) nor flags are set.In fact, it either does
nothing at all or performs incorrect operations.
Therefore, should we mandate that non-CPU devices must provide a
get_cost callback?
So Should we add a check at the beginning of the em_compute_costs() to:
if (!_is_cpu_device(dev) && !cb->get_cost) {
dev_dbg(dev, "EM: No get_cost provided, cost unset.\n");
return 0;
}
And Modify em_dev_compute_costs() to require callers to provide the cb
callback function,Also need to update its corresponding comments.
>> /* increase resolution of 'cost' precision */
>> power_res = table[i].power * 10;
>> cost = power_res / table[i].performance;
>> --
On Wed, Apr 16, 2025 at 4:57 AM Yaxiong Tian <iambestgod@qq.com> wrote:
>
> 在 2025/4/16 01:17, Rafael J. Wysocki 写道:
> > On Mon, Apr 14, 2025 at 11:09 AM Yaxiong Tian <iambestgod@qq.com> wrote:
> >>
> >> From: Yaxiong Tian <tianyaxiong@kylinos.cn>
> >>
> >> When the device is of a non-CPU type, table[i].performance won't be
> >> initialized in the previous em_init_performance(), resulting in division
> >> by zero when calculating costs in em_compute_costs().
> >>
> >> Since the 'cost' algorithm is only used for EAS energy efficiency
> >> calculations and is currently not utilized by other device drivers, we
> >> should add the _is_cpu_device(dev) check to prevent this division-by-zero
> >> issue.
> >>
> >> Fixes: <1b600da51073> ("PM: EM: Optimize em_cpu_energy() and remove division")
> >
> > Please look at the Fixes: tags in the kernel git history. They don't
> > look like the one above.
> >
> Yes, there's an extra '<>' here.
>
> >> Signed-off-by: Yaxiong Tian <tianyaxiong@kylinos.cn>
> >> ---
> >> kernel/power/energy_model.c | 4 ++--
> >> 1 file changed, 2 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/kernel/power/energy_model.c b/kernel/power/energy_model.c
> >> index d9b7e2b38c7a..fc972cc1fc12 100644
> >> --- a/kernel/power/energy_model.c
> >> +++ b/kernel/power/energy_model.c
> >> @@ -235,7 +235,7 @@ static int em_compute_costs(struct device *dev, struct em_perf_state *table,
> >>
> >> /* Compute the cost of each performance state. */
> >> for (i = nr_states - 1; i >= 0; i--) {
> >> - unsigned long power_res, cost;
> >> + unsigned long power_res, cost = 0;
> >>
> >> if ((flags & EM_PERF_DOMAIN_ARTIFICIAL) && cb->get_cost) {
> >> ret = cb->get_cost(dev, table[i].frequency, &cost);
> >> @@ -244,7 +244,7 @@ static int em_compute_costs(struct device *dev, struct em_perf_state *table,
> >> cost, ret);
> >> return -EINVAL;
> >> }
> >> - } else {
> >> + } else if (_is_cpu_device(dev)) {
> >
> > Can't you just check this upfront at the beginning of the function and
> > make it bail out if dev is not a CPU device?
> >
> Sure, But the current implementation applies em_compute_costs() to both
> non-CPU devices and CPU devices.
Maybe it shouldn't do that for non-CPU ones?
> After carefully reviewing the latest code,
> I've found this issue has expanded in scope.
>
> There are currently three call paths for invoking em_compute_costs():
>
> 1) Registering performance domains (for both non-CPU and CPU devices)
> em_dev_register_perf_domain() → em_create_pd() →
> em_create_perf_table() → em_compute_costs()
>
> 2)EM update paths (CPU devices only)
>
> Periodic 1000ms update check via em_update_work work item:
> em_check_capacity_update() → em_adjust_new_capacity() →
> em_recalc_and_update() → em_compute_costs()
>
> Exynos-chip initialization:
> em_dev_update_chip_binning() → em_recalc_and_update() → em_compute_costs()
>
> 3) Device cost computation (non-CPU devices only - currently unused)
> em_dev_compute_costs() → em_compute_costs()
So because this one is unused and AFAICS the cost values are never
used for non-CPU devices, it's better to just avoid computing them at
all.
> Note: In em_dev_compute_costs(), when calling em_compute_costs(),
> neither the callback (cb) nor flags are set.In fact, it either does
> nothing at all or performs incorrect operations.
>
> Therefore, should we mandate that non-CPU devices must provide a
> get_cost callback?
Why would that be an improvement?
> So Should we add a check at the beginning of the em_compute_costs() to:
>
> if (!_is_cpu_device(dev) && !cb->get_cost) {
> dev_dbg(dev, "EM: No get_cost provided, cost unset.\n");
> return 0;
> }
> And Modify em_dev_compute_costs() to require callers to provide the cb
> callback function,Also need to update its corresponding comments.
>
>
> >> /* increase resolution of 'cost' precision */
> >> power_res = table[i].power * 10;
> >> cost = power_res / table[i].performance;
> >> --
I think until there is a user of em_dev_compute_costs() this is all
moot and hard to figure out.
I would drop em_dev_compute_costs() altogether for now and put a
_is_cpu_device(dev) upfront check into em_compute_costs().
在 2025/4/16 19:58, Rafael J. Wysocki 写道:
> On Wed, Apr 16, 2025 at 4:57 AM Yaxiong Tian <iambestgod@qq.com> wrote:
>>
>> 在 2025/4/16 01:17, Rafael J. Wysocki 写道:
>>> On Mon, Apr 14, 2025 at 11:09 AM Yaxiong Tian <iambestgod@qq.com> wrote:
>>>>
>>>> From: Yaxiong Tian <tianyaxiong@kylinos.cn>
>>>>
>>>> When the device is of a non-CPU type, table[i].performance won't be
>>>> initialized in the previous em_init_performance(), resulting in division
>>>> by zero when calculating costs in em_compute_costs().
>>>>
>>>> Since the 'cost' algorithm is only used for EAS energy efficiency
>>>> calculations and is currently not utilized by other device drivers, we
>>>> should add the _is_cpu_device(dev) check to prevent this division-by-zero
>>>> issue.
>>>>
>>>> Fixes: <1b600da51073> ("PM: EM: Optimize em_cpu_energy() and remove division")
>>>
>>> Please look at the Fixes: tags in the kernel git history. They don't
>>> look like the one above.
>>>
>> Yes, there's an extra '<>' here.
>>
>>>> Signed-off-by: Yaxiong Tian <tianyaxiong@kylinos.cn>
>>>> ---
>>>> kernel/power/energy_model.c | 4 ++--
>>>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/kernel/power/energy_model.c b/kernel/power/energy_model.c
>>>> index d9b7e2b38c7a..fc972cc1fc12 100644
>>>> --- a/kernel/power/energy_model.c
>>>> +++ b/kernel/power/energy_model.c
>>>> @@ -235,7 +235,7 @@ static int em_compute_costs(struct device *dev, struct em_perf_state *table,
>>>>
>>>> /* Compute the cost of each performance state. */
>>>> for (i = nr_states - 1; i >= 0; i--) {
>>>> - unsigned long power_res, cost;
>>>> + unsigned long power_res, cost = 0;
>>>>
>>>> if ((flags & EM_PERF_DOMAIN_ARTIFICIAL) && cb->get_cost) {
>>>> ret = cb->get_cost(dev, table[i].frequency, &cost);
>>>> @@ -244,7 +244,7 @@ static int em_compute_costs(struct device *dev, struct em_perf_state *table,
>>>> cost, ret);
>>>> return -EINVAL;
>>>> }
>>>> - } else {
>>>> + } else if (_is_cpu_device(dev)) {
>>>
>>> Can't you just check this upfront at the beginning of the function and
>>> make it bail out if dev is not a CPU device?
>>>
>> Sure, But the current implementation applies em_compute_costs() to both
>> non-CPU devices and CPU devices.
>
> Maybe it shouldn't do that for non-CPU ones?
>
>> After carefully reviewing the latest code,
>> I've found this issue has expanded in scope.
>>
>> There are currently three call paths for invoking em_compute_costs():
>>
>> 1) Registering performance domains (for both non-CPU and CPU devices)
>> em_dev_register_perf_domain() → em_create_pd() →
>> em_create_perf_table() → em_compute_costs()
>>
>> 2)EM update paths (CPU devices only)
>>
>> Periodic 1000ms update check via em_update_work work item:
>> em_check_capacity_update() → em_adjust_new_capacity() →
>> em_recalc_and_update() → em_compute_costs()
>>
>> Exynos-chip initialization:
>> em_dev_update_chip_binning() → em_recalc_and_update() → em_compute_costs()
>>
>> 3) Device cost computation (non-CPU devices only - currently unused)
>> em_dev_compute_costs() → em_compute_costs()
>
> So because this one is unused and AFAICS the cost values are never
> used for non-CPU devices, it's better to just avoid computing them at
> all.
>
>> Note: In em_dev_compute_costs(), when calling em_compute_costs(),
>> neither the callback (cb) nor flags are set.In fact, it either does
>> nothing at all or performs incorrect operations.
>>
>> Therefore, should we mandate that non-CPU devices must provide a
>> get_cost callback?
>
> Why would that be an improvement?
>
>> So Should we add a check at the beginning of the em_compute_costs() to:
>>
>> if (!_is_cpu_device(dev) && !cb->get_cost) {
>> dev_dbg(dev, "EM: No get_cost provided, cost unset.\n");
>> return 0;
>> }
>> And Modify em_dev_compute_costs() to require callers to provide the cb
>> callback function,Also need to update its corresponding comments.
>>
>>
>>>> /* increase resolution of 'cost' precision */
>>>> power_res = table[i].power * 10;
>>>> cost = power_res / table[i].performance;
>>>> --
>
> I think until there is a user of em_dev_compute_costs() this is all
> moot and hard to figure out.
>
> I would drop em_dev_compute_costs() altogether for now and put a
> _is_cpu_device(dev) upfront check into em_compute_costs().
Yes, I agree with your point. Currently no non-CPU devices are using
'cost'. The best approach would be to just add the _is_cpu_device check.
I'll update it in V4.
By the way, em_dev_compute_costs should only apply to CPU devices. I was
mistaken earlier—it’s really hard to tell just from the function name.
On 4/16/25 12:58, Rafael J. Wysocki wrote:
> On Wed, Apr 16, 2025 at 4:57 AM Yaxiong Tian <iambestgod@qq.com> wrote:
>>
>> 在 2025/4/16 01:17, Rafael J. Wysocki 写道:
>>> On Mon, Apr 14, 2025 at 11:09 AM Yaxiong Tian <iambestgod@qq.com> wrote:
>>>>
>>>> From: Yaxiong Tian <tianyaxiong@kylinos.cn>
>>>>
>>>> When the device is of a non-CPU type, table[i].performance won't be
>>>> initialized in the previous em_init_performance(), resulting in division
>>>> by zero when calculating costs in em_compute_costs().
>>>>
>>>> Since the 'cost' algorithm is only used for EAS energy efficiency
>>>> calculations and is currently not utilized by other device drivers, we
>>>> should add the _is_cpu_device(dev) check to prevent this division-by-zero
>>>> issue.
>>>>
>>>> Fixes: <1b600da51073> ("PM: EM: Optimize em_cpu_energy() and remove division")
>>>
>>> Please look at the Fixes: tags in the kernel git history. They don't
>>> look like the one above.
>>>
>> Yes, there's an extra '<>' here.
>>
>>>> Signed-off-by: Yaxiong Tian <tianyaxiong@kylinos.cn>
>>>> ---
>>>> kernel/power/energy_model.c | 4 ++--
>>>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/kernel/power/energy_model.c b/kernel/power/energy_model.c
>>>> index d9b7e2b38c7a..fc972cc1fc12 100644
>>>> --- a/kernel/power/energy_model.c
>>>> +++ b/kernel/power/energy_model.c
>>>> @@ -235,7 +235,7 @@ static int em_compute_costs(struct device *dev, struct em_perf_state *table,
>>>>
>>>> /* Compute the cost of each performance state. */
>>>> for (i = nr_states - 1; i >= 0; i--) {
>>>> - unsigned long power_res, cost;
>>>> + unsigned long power_res, cost = 0;
>>>>
>>>> if ((flags & EM_PERF_DOMAIN_ARTIFICIAL) && cb->get_cost) {
>>>> ret = cb->get_cost(dev, table[i].frequency, &cost);
>>>> @@ -244,7 +244,7 @@ static int em_compute_costs(struct device *dev, struct em_perf_state *table,
>>>> cost, ret);
>>>> return -EINVAL;
>>>> }
>>>> - } else {
>>>> + } else if (_is_cpu_device(dev)) {
>>>
>>> Can't you just check this upfront at the beginning of the function and
>>> make it bail out if dev is not a CPU device?
>>>
>> Sure, But the current implementation applies em_compute_costs() to both
>> non-CPU devices and CPU devices.
>
> Maybe it shouldn't do that for non-CPU ones?
It shouldn't call this cost computation for non-CPU devices.
Let me check that.
On 4/14/25 10:04, Yaxiong Tian wrote:
> From: Yaxiong Tian <tianyaxiong@kylinos.cn>
>
> When the device is of a non-CPU type, table[i].performance won't be
> initialized in the previous em_init_performance(), resulting in division
> by zero when calculating costs in em_compute_costs().
>
> Since the 'cost' algorithm is only used for EAS energy efficiency
> calculations and is currently not utilized by other device drivers, we
> should add the _is_cpu_device(dev) check to prevent this division-by-zero
> issue.
>
> Fixes: <1b600da51073> ("PM: EM: Optimize em_cpu_energy() and remove division")
> Signed-off-by: Yaxiong Tian <tianyaxiong@kylinos.cn>
> ---
> kernel/power/energy_model.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/power/energy_model.c b/kernel/power/energy_model.c
> index d9b7e2b38c7a..fc972cc1fc12 100644
> --- a/kernel/power/energy_model.c
> +++ b/kernel/power/energy_model.c
> @@ -235,7 +235,7 @@ static int em_compute_costs(struct device *dev, struct em_perf_state *table,
>
> /* Compute the cost of each performance state. */
> for (i = nr_states - 1; i >= 0; i--) {
> - unsigned long power_res, cost;
> + unsigned long power_res, cost = 0;
>
> if ((flags & EM_PERF_DOMAIN_ARTIFICIAL) && cb->get_cost) {
> ret = cb->get_cost(dev, table[i].frequency, &cost);
> @@ -244,7 +244,7 @@ static int em_compute_costs(struct device *dev, struct em_perf_state *table,
> cost, ret);
> return -EINVAL;
> }
> - } else {
> + } else if (_is_cpu_device(dev)) {
> /* increase resolution of 'cost' precision */
> power_res = table[i].power * 10;
> cost = power_res / table[i].performance;
LGTM,
Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>
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