On 2023/5/15 18:00, Zeng Heng wrote:
> As ARM AMU's document says, all counters are subject to any changes
> in clock frequency, including clock stopping caused by the WFI and WFE
> instructions.
>
> Therefore, using smp_call_function_single() to trigger target CPU to
> read self's AMU counters, which ensures the counters are working
> properly during calculation.
>
> Signed-off-by: Zeng Heng <zengheng4@xxxxxxxxxx>
> ---
> drivers/cpufreq/cppc_cpufreq.c | 30 ++++++++++++++++--------------
> 1 file changed, 16 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
> index 022e3555407c..169af7ff9a2a 100644
> --- a/drivers/cpufreq/cppc_cpufreq.c
> +++ b/drivers/cpufreq/cppc_cpufreq.c
> @@ -837,29 +837,31 @@ static int cppc_perf_from_fbctrs(struct cppc_cpudata *cpu_data,
> return (reference_perf * delta_delivered) / delta_reference;
> }
>
> +static void cppc_get_perf_ctrs_smp(void *val)
> +{
> + int cpu = smp_processor_id();
> + struct cppc_perf_fb_ctrs *fb_ctrs = val;
> +
> + cppc_get_perf_ctrs(cpu, fb_ctrs);
> +
> + udelay(2); /* 2usec delay between sampling */
> +
> + cppc_get_perf_ctrs(cpu, fb_ctrs + 1);
> +}
> +
> static unsigned int cppc_cpufreq_get_rate(unsigned int cpu)
> {
> - struct cppc_perf_fb_ctrs fb_ctrs_t0 = {0}, fb_ctrs_t1 = {0};
> + struct cppc_perf_fb_ctrs fb_ctrs[2] = {0};
> struct cpufreq_policy *policy = cpufreq_cpu_get(cpu);
> struct cppc_cpudata *cpu_data = policy->driver_data;
> u64 delivered_perf;
> - int ret;
>
> cpufreq_cpu_put(policy);
>
> - ret = cppc_get_perf_ctrs(cpu, &fb_ctrs_t0);
> - if (ret)
> - return ret;
> -
> - udelay(2); /* 2usec delay between sampling */
> -
> - ret = cppc_get_perf_ctrs(cpu, &fb_ctrs_t1);
> - if (ret)
> - return ret;
> -
> - delivered_perf = cppc_perf_from_fbctrs(cpu_data, &fb_ctrs_t0,
> - &fb_ctrs_t1);
> + smp_call_function_single(cpu, cppc_get_perf_ctrs_smp, fb_ctrs, 1);
cppc_get_perf_ctrs() may call down_write(), while the callback for smp_call_function_single()
should be non-blocking, you can use smp_call_on_cpu() instead.
>
> + delivered_perf = cppc_perf_from_fbctrs(cpu_data, fb_ctrs,
> + fb_ctrs + 1);
> return cppc_cpufreq_perf_to_khz(cpu_data, delivered_perf);
> }
>
