On Tue, Mar 15, 2022 at 3:30 AM zhengzucheng zhengzucheng@huawei.com wrote:
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.
Which driver? Again, there is only one calling cpufreq_get() in the kernel tree and it is not on x86.
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);--
The answer to my question appears to be that you want cpufreq_get() to be consistent with show_scaling_cur_freq().
Fair enough, but in that case please make them both call the same lower-level routine implementing the desired behavior so as to avoid code duplication.