Messages in this thread | | | Subject | Re: [PATCH v3 4/5] cpufreq: qcom-cpufreq-hw: Use new thermal pressure update function | From | Lukasz Luba <> | Date | Mon, 8 Nov 2021 14:12:29 +0000 |
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Hi Thara,
+CC Steev, who discovered this issue with boost frequency
On 11/5/21 7:12 PM, Thara Gopinath wrote: > Hi Lukasz, > > > On 11/3/21 12:10 PM, Lukasz Luba wrote: >> Thermal pressure provides a new API, which allows to use CPU frequency >> as an argument. That removes the need of local conversion to capacity. >> Use this new API and remove old local conversion code. >> >> Signed-off-by: Lukasz Luba <lukasz.luba@arm.com> >> --- >> drivers/cpufreq/qcom-cpufreq-hw.c | 15 +++++---------- >> 1 file changed, 5 insertions(+), 10 deletions(-) >> >> diff --git a/drivers/cpufreq/qcom-cpufreq-hw.c >> b/drivers/cpufreq/qcom-cpufreq-hw.c >> index 0138b2ec406d..425f351450ad 100644 >> --- a/drivers/cpufreq/qcom-cpufreq-hw.c >> +++ b/drivers/cpufreq/qcom-cpufreq-hw.c >> @@ -275,10 +275,10 @@ static unsigned int >> qcom_lmh_get_throttle_freq(struct qcom_cpufreq_data *data) >> static void qcom_lmh_dcvs_notify(struct qcom_cpufreq_data *data) >> { >> - unsigned long max_capacity, capacity, freq_hz, throttled_freq; >> struct cpufreq_policy *policy = data->policy; >> int cpu = cpumask_first(policy->cpus); >> struct device *dev = get_cpu_device(cpu); >> + unsigned long freq_hz, throttled_freq; >> struct dev_pm_opp *opp; >> unsigned int freq; >> @@ -295,17 +295,12 @@ static void qcom_lmh_dcvs_notify(struct >> qcom_cpufreq_data *data) >> throttled_freq = freq_hz / HZ_PER_KHZ; >> - /* Update thermal pressure */ >> - >> - max_capacity = arch_scale_cpu_capacity(cpu); >> - capacity = mult_frac(max_capacity, throttled_freq, >> policy->cpuinfo.max_freq); >> - >> /* Don't pass boost capacity to scheduler */ >> - if (capacity > max_capacity) >> - capacity = max_capacity; > > So, I think this should go into the common > topology_update_thermal_pressure in lieu of > > + if (WARN_ON(max_freq < capped_freq)) > + return; > > This will fix the issue Steev Klimaszewski has been reporting > https://lore.kernel.org/linux-arm-kernel/3cba148a-7077-7b6b-f131-dc65045aa348@arm.com/ > > >
Well, I think the issue is broader. Look at the code which calculate this 'capacity'. It's just a multiplication & division:
max_capacity = arch_scale_cpu_capacity(cpu); // =1024 in our case capacity = mult_frac(max_capacity, throttled_freq, policy->cpuinfo.max_freq);
In the reported by Steev output from sysfs cpufreq we know that the value of 'policy->cpuinfo.max_freq' is: /sys/devices/system/cpu/cpu5/cpufreq/cpuinfo_max_freq:2956800
so when we put the values to the equation we get: capacity = 1024 * 2956800 / 2956800; // =1024 The 'capacity' will be always <= 1024 and this check won't be triggered:
/* Don't pass boost capacity to scheduler */ if (capacity > max_capacity) capacity = max_capacity;
IIUC you original code, you don't want to have this boost frequency to be treated as 1024 capacity. The reason is because the whole capacity machinery in arch_topology.c is calculated based on max freq value = 2841600, so the max capacity 1024 would be pinned to that frequency (according to Steeve's log: [ 22.552273] THERMAL_PRESSURE: max_freq(2841) < capped_freq(2956) for CPUs [4-7] )
Having all this in mind, the multiplication and division in your original code should be done:
capacity = 1024 * 2956800 / 2841600; // = 1065
then clamped to 1024 value.
My change just unveiled this division issue.
With that in mind, I tend to agree that I should have not rely on passed boost freq value and try to apply your suggestion check. Let me experiment with that...
Regards, Lukasz
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