Messages in this thread | | | Date | Wed, 3 Jun 2020 13:22:00 +0530 | From | Viresh Kumar <> | Subject | Re: [Question]: about 'cpuinfo_cur_freq' shown in sysfs when the CPU is in idle state |
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On 02-06-20, 11:34, Xiongfeng Wang wrote: > Hi Viresh, > > Sorry to disturb you about another problem as follows. > > CPPC use the increment of Desired Performance counter and Reference Performance > counter to get the CPU frequency and show it in sysfs through > 'cpuinfo_cur_freq'. But ACPI CPPC doesn't specifically define the behavior of > these two counters when the CPU is in idle state, such as stop incrementing when > the CPU is in idle state. > > ARMv8.4 Extension inctroduced support for the Activity Monitors Unit (AMU). The > processor frequency cycles and constant frequency cycles in AMU can be used as > Delivered Performance counter and Reference Performance counter. These two > counter in AMU does not increase when the PE is in WFI or WFE. So the increment > is zero when the PE is in WFI/WFE. This cause no issue because > 'cppc_get_rate_from_fbctrs()' in cppc_cpufreq driver will check the increment > and return the desired performance if the increment is zero. > > But when the CPU goes into power down idle state, accessing these two counters > in AMU by memory-mapped address will return zero. Such as CPU1 went into power > down idle state and CPU0 try to get the frequency of CPU1. In this situation, > will display a very big value for 'cpuinfo_cur_freq' in sysfs. Do you have some > advice about this problem ? > > I was thinking about an idea as follows. We can run 'cppc_cpufreq_get_rate()' on > the CPU to be measured, so that we can make sure the CPU is in C0 state when we > access the two counters. Also we can return the actual frequency rather than > desired performance when the CPU is in WFI/WFE. But this modification will > change the existing logical and I am not sure if this will cause some bad effect. > > > diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c > index 257d726..ded3bcc 100644 > --- a/drivers/cpufreq/cppc_cpufreq.c > +++ b/drivers/cpufreq/cppc_cpufreq.c > @@ -396,9 +396,10 @@ static int cppc_get_rate_from_fbctrs(struct cppc_cpudata *cpu, > return cppc_cpufreq_perf_to_khz(cpu, delivered_perf); > } > > -static unsigned int cppc_cpufreq_get_rate(unsigned int cpunum) > +static int cppc_cpufreq_get_rate_cpu(void *info) > { > struct cppc_perf_fb_ctrs fb_ctrs_t0 = {0}, fb_ctrs_t1 = {0}; > + unsigned int cpunum = *(unsigned int *)info; > struct cppc_cpudata *cpu = all_cpu_data[cpunum]; > int ret; > > @@ -418,6 +419,22 @@ static unsigned int cppc_cpufreq_get_rate(unsigned int cpunum) > return cppc_get_rate_from_fbctrs(cpu, fb_ctrs_t0, fb_ctrs_t1); > } > > +static unsigned int cppc_cpufreq_get_rate(unsigned int cpunum) > +{ > + unsigned int ret; > + > + ret = smp_call_on_cpu(cpunum, cppc_cpufreq_get_rate_cpu, &cpunum, true); > + > + /* > + * convert negative error code to zero, otherwise we will display > + * an odd value for 'cpuinfo_cur_freq' in sysfs > + */ > + if (ret < 0) > + ret = 0; > + > + return ret; > +} > + > static int cppc_cpufreq_set_boost(struct cpufreq_policy *policy, int state) > { > struct cppc_cpudata *cpudata;
I don't see any other sane solution, even if this brings the CPU back to normal state and waste power. We should be able to reliably provide value to userspace.
Rafael / Sudeep: What you do say ?
-- viresh
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