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| author | Lukasz Luba <lukasz.luba@arm.com> | 2022-07-07 09:15:52 +0200 |
|---|---|---|
| committer | Rafael J. Wysocki <rafael.j.wysocki@intel.com> | 2022-07-15 19:17:30 +0200 |
| commit | ae6ccaa650380d243cf43d31c864c5ced2fd4612 (patch) | |
| tree | 31a1316e5a8e779db5d4697fa05bb43853fed24a /drivers/powercap | |
| parent | Linux 5.19-rc6 (diff) | |
| download | linux-ae6ccaa650380d243cf43d31c864c5ced2fd4612.tar.xz linux-ae6ccaa650380d243cf43d31c864c5ced2fd4612.zip | |
PM: EM: convert power field to micro-Watts precision and align drivers
The milli-Watts precision causes rounding errors while calculating
efficiency cost for each OPP. This is especially visible in the 'simple'
Energy Model (EM), where the power for each OPP is provided from OPP
framework. This can cause some OPPs to be marked inefficient, while
using micro-Watts precision that might not happen.
Update all EM users which access 'power' field and assume the value is
in milli-Watts.
Solve also an issue with potential overflow in calculation of energy
estimation on 32bit machine. It's needed now since the power value
(thus the 'cost' as well) are higher.
Example calculation which shows the rounding error and impact:
power = 'dyn-power-coeff' * volt_mV * volt_mV * freq_MHz
power_a_uW = (100 * 600mW * 600mW * 500MHz) / 10^6 = 18000
power_a_mW = (100 * 600mW * 600mW * 500MHz) / 10^9 = 18
power_b_uW = (100 * 605mW * 605mW * 600MHz) / 10^6 = 21961
power_b_mW = (100 * 605mW * 605mW * 600MHz) / 10^9 = 21
max_freq = 2000MHz
cost_a_mW = 18 * 2000MHz/500MHz = 72
cost_a_uW = 18000 * 2000MHz/500MHz = 72000
cost_b_mW = 21 * 2000MHz/600MHz = 70 // <- artificially better
cost_b_uW = 21961 * 2000MHz/600MHz = 73203
The 'cost_b_mW' (which is based on old milli-Watts) is misleadingly
better that the 'cost_b_uW' (this patch uses micro-Watts) and such
would have impact on the 'inefficient OPPs' information in the Cpufreq
framework. This patch set removes the rounding issue.
Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Diffstat (limited to 'drivers/powercap')
| -rw-r--r-- | drivers/powercap/dtpm_cpu.c | 5 |
1 files changed, 2 insertions, 3 deletions
diff --git a/drivers/powercap/dtpm_cpu.c b/drivers/powercap/dtpm_cpu.c index f5eced0842b3..61c5ff80bd30 100644 --- a/drivers/powercap/dtpm_cpu.c +++ b/drivers/powercap/dtpm_cpu.c @@ -53,7 +53,7 @@ static u64 set_pd_power_limit(struct dtpm *dtpm, u64 power_limit) for (i = 0; i < pd->nr_perf_states; i++) { - power = pd->table[i].power * MICROWATT_PER_MILLIWATT * nr_cpus; + power = pd->table[i].power * nr_cpus; if (power > power_limit) break; @@ -63,8 +63,7 @@ static u64 set_pd_power_limit(struct dtpm *dtpm, u64 power_limit) freq_qos_update_request(&dtpm_cpu->qos_req, freq); - power_limit = pd->table[i - 1].power * - MICROWATT_PER_MILLIWATT * nr_cpus; + power_limit = pd->table[i - 1].power * nr_cpus; return power_limit; } |