| Message ID | 20210720094153.31097-2-lukasz.luba@arm.com |
|---|---|
| State | Superseded |
| Headers | show |
| Series | Improve EAS energy estimation and increase precision | expand |
Hi Peter, Vincent, Gentle ping. On 7/20/21 10:41 AM, Lukasz Luba wrote: > The Energy Model (EM) provides useful information about device power in > each performance state to other subsystems like: Energy Aware Scheduler > (EAS). The energy calculation in EAS does arithmetic operation based on > the EM em_cpu_energy(). Current implementation of that function uses > em_perf_state::cost as a pre-computed cost coefficient equal to: > cost = power * max_frequency / frequency. > The 'power' is expressed in milli-Watts (or in abstract scale). > > There are corner cases when the EAS energy calculation for two Performance > Domains (PDs) return the same value. The EAS compares these values to > choose smaller one. It might happen that this values are equal due to > rounding error. In such scenario, we need better resolution, e.g. 1000 > times better. To provide this possibility increase the resolution in the > em_perf_state::cost for 64-bit architectures. The costs for increasing > resolution in 32-bit architectures are pretty high (64-bit division) and > the returns do not justify the increased costs. > > This patch allows to avoid the rounding to milli-Watt errors, which might > occur in EAS energy estimation for each Performance Domains (PD). The > rounding error is common for small tasks which have small utilization > value. > > There are two places in the code where it makes a difference: > 1. In the find_energy_efficient_cpu() where we are searching for > best_delta. We might suffer there when two PDs return the same result, > like in the example below. > > Scenario: > Low utilized system e.g. ~200 sum_util for PD0 and ~220 for PD1. There > are quite a few small tasks ~10-15 util. These tasks would suffer for > the rounding error. Such system utilization has been seen while playing > some simple games. In such condition our partner reported 5..10mA less > battery drain. > > Some details: > We have two Perf Domains (PDs): PD0 (big) and PD1 (little) > Let's compare w/o patch set ('old') and w/ patch set ('new') > We are comparing energy w/ task and w/o task placed in the PDs > > a) 'old' w/o patch set, PD0 > task_util = 13 > cost = 480 > sum_util_w/o_task = 215 > sum_util_w_task = 228 > scale_cpu = 1024 > energy_w/o_task = 480 * 215 / 1024 = 100.78 => 100 > energy_w_task = 480 * 228 / 1024 = 106.87 => 106 > energy_diff = 106 - 100 = 6 > (this is equal to 'old' PD1's energy_diff in 'c)') > > b) 'new' w/ patch set, PD0 > task_util = 13 > cost = 480 * 1000 = 480000 > sum_util_w/o_task = 215 > sum_util_w_task = 228 > energy_w/o_task = 480000 * 215 / 1024 = 100781 > energy_w_task = 480000 * 228 / 1024 = 106875 > energy_diff = 106875 - 100781 = 6094 > (this is not equal to 'new' PD1's energy_diff in 'd)') > > c) 'old' w/o patch set, PD1 > task_util = 13 > cost = 160 > sum_util_w/o_task = 283 > sum_util_w_task = 293 > scale_cpu = 355 > energy_w/o_task = 160 * 283 / 355 = 127.55 => 127 > energy_w_task = 160 * 296 / 355 = 133.41 => 133 > energy_diff = 133 - 127 = 6 > (this is equal to 'old' PD0's energy_diff in 'a)') > > d) 'new' w/ patch set, PD1 > task_util = 13 > cost = 160 * 1000 = 160000 > sum_util_w/o_task = 283 > sum_util_w_task = 293 > scale_cpu = 355 > energy_w/o_task = 160000 * 283 / 355 = 127549 > energy_w_task = 160000 * 296 / 355 = 133408 > energy_diff = 133408 - 127549 = 5859 > (this is not equal to 'new' PD0's energy_diff in 'b)') > > 2. Difference in the the last find_energy_efficient_cpu(): margin filter. > With this patch the margin comparison also has better resolution, > so it's possible to have better task placement thanks to that. > > Fixes: 27871f7a8a341ef ("PM: Introduce an Energy Model management framework") > Reported-by: CCJ Yeh <CCj.Yeh@mediatek.com> > Signed-off-by: Lukasz Luba <lukasz.luba@arm.com> > --- > include/linux/energy_model.h | 16 ++++++++++++++++ > kernel/power/energy_model.c | 3 ++- > 2 files changed, 18 insertions(+), 1 deletion(-) > > diff --git a/include/linux/energy_model.h b/include/linux/energy_model.h > index 3f221dbf5f95..1834752c5617 100644 > --- a/include/linux/energy_model.h > +++ b/include/linux/energy_model.h > @@ -53,6 +53,22 @@ struct em_perf_domain { > #ifdef CONFIG_ENERGY_MODEL > #define EM_MAX_POWER 0xFFFF > > +/* > + * Increase resolution of energy estimation calculations for 64-bit > + * architectures. The extra resolution improves decision made by EAS for the > + * task placement when two Performance Domains might provide similar energy > + * estimation values (w/o better resolution the values could be equal). > + * > + * We increase resolution only if we have enough bits to allow this increased > + * resolution (i.e. 64-bit). The costs for increasing resolution when 32-bit > + * are pretty high and the returns do not justify the increased costs. > + */ > +#ifdef CONFIG_64BIT > +#define em_scale_power(p) ((p) * 1000) > +#else > +#define em_scale_power(p) (p) > +#endif > + > struct em_data_callback { > /** > * active_power() - Provide power at the next performance state of > diff --git a/kernel/power/energy_model.c b/kernel/power/energy_model.c > index 0f4530b3a8cd..bf312c04c514 100644 > --- a/kernel/power/energy_model.c > +++ b/kernel/power/energy_model.c > @@ -170,7 +170,8 @@ static int em_create_perf_table(struct device *dev, struct em_perf_domain *pd, > /* Compute the cost of each performance state. */ > fmax = (u64) table[nr_states - 1].frequency; > for (i = 0; i < nr_states; i++) { > - table[i].cost = div64_u64(fmax * table[i].power, > + unsigned long power_res = em_scale_power(table[i].power); > + table[i].cost = div64_u64(fmax * power_res, > table[i].frequency); > } > > Do you have any comments to this patch? It's EM-only change now, no other files touched. If it's OK, I will ask Rafael to take it. Regards, Lukasz
On 02/08/2021 08:21, Lukasz Luba wrote: > Hi Peter, Vincent, > > Gentle ping. > > > On 7/20/21 10:41 AM, Lukasz Luba wrote: [...] >> There are corner cases when the EAS energy calculation for two >> Performance >> Domains (PDs) return the same value. The EAS compares these values to >> choose smaller one. It might happen that this values are equal due to >> rounding error. In such scenario, we need better resolution, e.g. 1000 >> times better. To provide this possibility increase the resolution in the >> em_perf_state::cost for 64-bit architectures. The costs for increasing >> resolution in 32-bit architectures are pretty high (64-bit division) and >> the returns do not justify the increased costs. s/The costs ... increased costs./The cost of increasing resolution on 32-bit is pretty high (64-bit division) and is not justified since there are no new 32bit big.LITTLE EAS systems expected which would benefit from this higher resolution./ ? >> This patch allows to avoid the rounding to milli-Watt errors, which might >> occur in EAS energy estimation for each Performance Domains (PD). The s/Performance Domains (PD)/PD. [...] >> Scenario: >> Low utilized system e.g. ~200 sum_util for PD0 and ~220 for PD1. There >> are quite a few small tasks ~10-15 util. These tasks would suffer for >> the rounding error. Such system utilization has been seen while playing >> some simple games. In such condition our partner reported 5..10mA less >> battery drain. Hard to digest: Maybe s/Such system ... battery drain./These utilization values are typical when running games on Android. One of our partners has reported 5..10mA less battery drain when running with increased resolution./ ? >> >> Some details: >> We have two Perf Domains (PDs): PD0 (big) and PD1 (little) s/Perf Domains (PDs)/PDs [...] >> 2. Difference in the the last find_energy_efficient_cpu(): margin filter. s/in the the last find_energy_efficient_cpu(): margin filter/in the 6% energy margin filter at the end of find_energy_efficient_cpu()/ ? >> With this patch the margin comparison also has better resolution, >> so it's possible to have better task placement thanks to that. >> >> Fixes: 27871f7a8a341ef ("PM: Introduce an Energy Model management >> framework") >> Reported-by: CCJ Yeh <CCj.Yeh@mediatek.com> >> Signed-off-by: Lukasz Luba <lukasz.luba@arm.com> >> --- >> include/linux/energy_model.h | 16 ++++++++++++++++ >> kernel/power/energy_model.c | 3 ++- >> 2 files changed, 18 insertions(+), 1 deletion(-) >> >> diff --git a/include/linux/energy_model.h b/include/linux/energy_model.h >> index 3f221dbf5f95..1834752c5617 100644 >> --- a/include/linux/energy_model.h >> +++ b/include/linux/energy_model.h >> @@ -53,6 +53,22 @@ struct em_perf_domain { >> #ifdef CONFIG_ENERGY_MODEL >> #define EM_MAX_POWER 0xFFFF >> +/* >> + * Increase resolution of energy estimation calculations for 64-bit >> + * architectures. The extra resolution improves decision made by EAS >> for the >> + * task placement when two Performance Domains might provide similar >> energy >> + * estimation values (w/o better resolution the values could be equal). >> + * >> + * We increase resolution only if we have enough bits to allow this >> increased >> + * resolution (i.e. 64-bit). The costs for increasing resolution when >> 32-bit >> + * are pretty high and the returns do not justify the increased costs. >> + */ >> +#ifdef CONFIG_64BIT >> +#define em_scale_power(p) ((p) * 1000) >> +#else >> +#define em_scale_power(p) (p) >> +#endif >> + >> struct em_data_callback { >> /** >> * active_power() - Provide power at the next performance state of >> diff --git a/kernel/power/energy_model.c b/kernel/power/energy_model.c >> index 0f4530b3a8cd..bf312c04c514 100644 >> --- a/kernel/power/energy_model.c >> +++ b/kernel/power/energy_model.c >> @@ -170,7 +170,8 @@ static int em_create_perf_table(struct device >> *dev, struct em_perf_domain *pd, >> /* Compute the cost of each performance state. */ >> fmax = (u64) table[nr_states - 1].frequency; >> for (i = 0; i < nr_states; i++) { >> - table[i].cost = div64_u64(fmax * table[i].power, >> + unsigned long power_res = em_scale_power(table[i].power); >> + table[i].cost = div64_u64(fmax * power_res, >> table[i].frequency); >> } Otherwise, LGTM. Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com> This is now an EM only patch (Task scheduler (i.e. CFS/EAS) is only effected via compute_energy() -> em_cpu_energy().
On 8/3/21 10:44 AM, Dietmar Eggemann wrote: > On 02/08/2021 08:21, Lukasz Luba wrote: >> Hi Peter, Vincent, >> >> Gentle ping. >> >> >> On 7/20/21 10:41 AM, Lukasz Luba wrote: > > [...] > >>> There are corner cases when the EAS energy calculation for two >>> Performance >>> Domains (PDs) return the same value. The EAS compares these values to >>> choose smaller one. It might happen that this values are equal due to >>> rounding error. In such scenario, we need better resolution, e.g. 1000 >>> times better. To provide this possibility increase the resolution in the >>> em_perf_state::cost for 64-bit architectures. The costs for increasing >>> resolution in 32-bit architectures are pretty high (64-bit division) and >>> the returns do not justify the increased costs. > > s/The costs ... increased costs./The cost of increasing resolution on > 32-bit is pretty high (64-bit division) and is not justified since there > are no new 32bit big.LITTLE EAS systems expected which would benefit > from this higher resolution./ ? Sounds better indeed. > >>> This patch allows to avoid the rounding to milli-Watt errors, which might >>> occur in EAS energy estimation for each Performance Domains (PD). The > > s/Performance Domains (PD)/PD. OK > > [...] > >>> Scenario: >>> Low utilized system e.g. ~200 sum_util for PD0 and ~220 for PD1. There >>> are quite a few small tasks ~10-15 util. These tasks would suffer for >>> the rounding error. Such system utilization has been seen while playing >>> some simple games. In such condition our partner reported 5..10mA less >>> battery drain. > > Hard to digest: Maybe s/Such system ... battery drain./These utilization > values are typical when running games on Android. One of our partners > has reported 5..10mA less battery drain when running with increased > resolution./ ? Sounds good. > >>> >>> Some details: >>> We have two Perf Domains (PDs): PD0 (big) and PD1 (little) > > s/Perf Domains (PDs)/PDs OK > > [...] > >>> 2. Difference in the the last find_energy_efficient_cpu(): margin filter. > > s/in the the last find_energy_efficient_cpu(): margin filter/in the 6% > energy margin filter at the end of find_energy_efficient_cpu()/ ? OK [snip] > > Otherwise, LGTM. > > Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com> Thank you Dietmar for the review. I'm going to send the v3. > > This is now an EM only patch (Task scheduler (i.e. CFS/EAS) is only > effected via compute_energy() -> em_cpu_energy(). > True it's EM only now, so I will ask Rafael to pick it.
diff --git a/include/linux/energy_model.h b/include/linux/energy_model.h index 3f221dbf5f95..1834752c5617 100644 --- a/include/linux/energy_model.h +++ b/include/linux/energy_model.h @@ -53,6 +53,22 @@ struct em_perf_domain { #ifdef CONFIG_ENERGY_MODEL #define EM_MAX_POWER 0xFFFF +/* + * Increase resolution of energy estimation calculations for 64-bit + * architectures. The extra resolution improves decision made by EAS for the + * task placement when two Performance Domains might provide similar energy + * estimation values (w/o better resolution the values could be equal). + * + * We increase resolution only if we have enough bits to allow this increased + * resolution (i.e. 64-bit). The costs for increasing resolution when 32-bit + * are pretty high and the returns do not justify the increased costs. + */ +#ifdef CONFIG_64BIT +#define em_scale_power(p) ((p) * 1000) +#else +#define em_scale_power(p) (p) +#endif + struct em_data_callback { /** * active_power() - Provide power at the next performance state of diff --git a/kernel/power/energy_model.c b/kernel/power/energy_model.c index 0f4530b3a8cd..bf312c04c514 100644 --- a/kernel/power/energy_model.c +++ b/kernel/power/energy_model.c @@ -170,7 +170,8 @@ static int em_create_perf_table(struct device *dev, struct em_perf_domain *pd, /* Compute the cost of each performance state. */ fmax = (u64) table[nr_states - 1].frequency; for (i = 0; i < nr_states; i++) { - table[i].cost = div64_u64(fmax * table[i].power, + unsigned long power_res = em_scale_power(table[i].power); + table[i].cost = div64_u64(fmax * power_res, table[i].frequency); }
The Energy Model (EM) provides useful information about device power in each performance state to other subsystems like: Energy Aware Scheduler (EAS). The energy calculation in EAS does arithmetic operation based on the EM em_cpu_energy(). Current implementation of that function uses em_perf_state::cost as a pre-computed cost coefficient equal to: cost = power * max_frequency / frequency. The 'power' is expressed in milli-Watts (or in abstract scale). There are corner cases when the EAS energy calculation for two Performance Domains (PDs) return the same value. The EAS compares these values to choose smaller one. It might happen that this values are equal due to rounding error. In such scenario, we need better resolution, e.g. 1000 times better. To provide this possibility increase the resolution in the em_perf_state::cost for 64-bit architectures. The costs for increasing resolution in 32-bit architectures are pretty high (64-bit division) and the returns do not justify the increased costs. This patch allows to avoid the rounding to milli-Watt errors, which might occur in EAS energy estimation for each Performance Domains (PD). The rounding error is common for small tasks which have small utilization value. There are two places in the code where it makes a difference: 1. In the find_energy_efficient_cpu() where we are searching for best_delta. We might suffer there when two PDs return the same result, like in the example below. Scenario: Low utilized system e.g. ~200 sum_util for PD0 and ~220 for PD1. There are quite a few small tasks ~10-15 util. These tasks would suffer for the rounding error. Such system utilization has been seen while playing some simple games. In such condition our partner reported 5..10mA less battery drain. Some details: We have two Perf Domains (PDs): PD0 (big) and PD1 (little) Let's compare w/o patch set ('old') and w/ patch set ('new') We are comparing energy w/ task and w/o task placed in the PDs a) 'old' w/o patch set, PD0 task_util = 13 cost = 480 sum_util_w/o_task = 215 sum_util_w_task = 228 scale_cpu = 1024 energy_w/o_task = 480 * 215 / 1024 = 100.78 => 100 energy_w_task = 480 * 228 / 1024 = 106.87 => 106 energy_diff = 106 - 100 = 6 (this is equal to 'old' PD1's energy_diff in 'c)') b) 'new' w/ patch set, PD0 task_util = 13 cost = 480 * 1000 = 480000 sum_util_w/o_task = 215 sum_util_w_task = 228 energy_w/o_task = 480000 * 215 / 1024 = 100781 energy_w_task = 480000 * 228 / 1024 = 106875 energy_diff = 106875 - 100781 = 6094 (this is not equal to 'new' PD1's energy_diff in 'd)') c) 'old' w/o patch set, PD1 task_util = 13 cost = 160 sum_util_w/o_task = 283 sum_util_w_task = 293 scale_cpu = 355 energy_w/o_task = 160 * 283 / 355 = 127.55 => 127 energy_w_task = 160 * 296 / 355 = 133.41 => 133 energy_diff = 133 - 127 = 6 (this is equal to 'old' PD0's energy_diff in 'a)') d) 'new' w/ patch set, PD1 task_util = 13 cost = 160 * 1000 = 160000 sum_util_w/o_task = 283 sum_util_w_task = 293 scale_cpu = 355 energy_w/o_task = 160000 * 283 / 355 = 127549 energy_w_task = 160000 * 296 / 355 = 133408 energy_diff = 133408 - 127549 = 5859 (this is not equal to 'new' PD0's energy_diff in 'b)') 2. Difference in the the last find_energy_efficient_cpu(): margin filter. With this patch the margin comparison also has better resolution, so it's possible to have better task placement thanks to that. Fixes: 27871f7a8a341ef ("PM: Introduce an Energy Model management framework") Reported-by: CCJ Yeh <CCj.Yeh@mediatek.com> Signed-off-by: Lukasz Luba <lukasz.luba@arm.com> --- include/linux/energy_model.h | 16 ++++++++++++++++ kernel/power/energy_model.c | 3 ++- 2 files changed, 18 insertions(+), 1 deletion(-)