Messages in this thread | | | Subject | Re: [PATCH] cpufreq: fix cpufreq_get() can't get correct CPU frequency | From | zhengzucheng <> | Date | Tue, 15 Mar 2022 10:30:23 +0800 |
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On 2022/3/11 23:52, Rafael J. Wysocki wrote: > On Fri, Mar 11, 2022 at 9:11 AM z00314508 <zhengzucheng@huawei.com> wrote: >> From: Zucheng Zheng <zhengzucheng@huawei.com> >> >> On some specific platforms, the cpufreq driver does not define >> cpufreq_driver.get() routine (eg:x86 intel_pstate driver), as a > I guess you mean the cpufreq driver ->get callback. > > No, intel_pstate doesn't implement it, because it cannot reliably > return the current CPU frequency. > >> result, the cpufreq_get() can't get the correct CPU frequency. > No, it can't, if intel_pstate is the driver, but what's the problem? > This function is only called in one place in the kernel and not on x8 > even. > >> Modern x86 processors include the hardware needed to accurately >> calculate frequency over an interval -- APERF, MPERF and the TSC. > You can compute the average frequency over an interval, but ->get is > expected to return the actual current frequency at the time call time. > >> Here we use arch_freq_get_on_cpu() in preference to any driver >> driver-specific cpufreq_driver.get() routine to get CPU frequency. >> >> Fixes: f8475cef9008 ("x86: use common aperfmperf_khz_on_cpu() to calculate KHz using APERF/MPERF") > No kidding. > >> Signed-off-by: Zucheng Zheng <zhengzucheng@huawei.com> >> --- >> drivers/cpufreq/cpufreq.c | 6 +++++- >> 1 file changed, 5 insertions(+), 1 deletion(-) >> >> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c >> index 80f535cc8a75..d777257b4454 100644 >> --- a/drivers/cpufreq/cpufreq.c >> +++ b/drivers/cpufreq/cpufreq.c >> @@ -1806,10 +1806,14 @@ unsigned int cpufreq_get(unsigned int cpu) >> { >> struct cpufreq_policy *policy = cpufreq_cpu_get(cpu); >> unsigned int ret_freq = 0; >> + unsigned int freq; >> >> if (policy) { >> down_read(&policy->rwsem); >> - if (cpufreq_driver->get) >> + freq = arch_freq_get_on_cpu(policy->cpu); >> + if (freq) >> + ret_freq = freq; >> + else if (cpufreq_driver->get) > Again, what problem exactly does this address? Thank you for review.
In some scenarios, cpufreq driver ->get is not defined, some driver get the CPU frequency by calling cpufreq_get() will return 0. The modification to this problem is inspired by the implementation of the show_scaling_cur_freq(). > >> ret_freq = __cpufreq_get(policy); >> up_read(&policy->rwsem); >> >> -- > . >
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