Hi George,
On 7/9/2018 4:10 AM, George Cherian wrote:
> Per Section 8.4.7.1.3 of ACPI 6.2, The platform provides performance
> feedback via set of performance counters. To determine the actual
> performance level delivered over time, OSPM may read a set of
> performance counters from the Reference Performance Counter Register
> and the Delivered Performance Counter Register.
>
> OSPM calculates the delivered performance over a given time period by
> taking a beginning and ending snapshot of both the reference and
> delivered performance counters, and calculating:
>
> delivered_perf = reference_perf X (delta of delivered_perf counter / delta of
> reference_perf counter).
>
> Implement the above and hook this to the cpufreq->get method.
>
> Signed-off-by: George Cherian <george.cher...@cavium.com>
> Acked-by: Viresh Kumar <viresh.ku...@linaro.org>
> ---
> drivers/cpufreq/cppc_cpufreq.c | 44
> ++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 44 insertions(+)
>
> diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
> index a9d3eec..61132e8 100644
> --- a/drivers/cpufreq/cppc_cpufreq.c
> +++ b/drivers/cpufreq/cppc_cpufreq.c
> @@ -296,10 +296,54 @@ static int cppc_cpufreq_cpu_init(struct cpufreq_policy
> *policy)
> return ret;
> }
>
> +static int cppc_get_rate_from_fbctrs(struct cppc_cpudata *cpu,
> + struct cppc_perf_fb_ctrs fb_ctrs_t0,
> + struct cppc_perf_fb_ctrs fb_ctrs_t1)
> +{
> + u64 delta_reference, delta_delivered;
> + u64 reference_perf, delivered_perf;
> +
> + reference_perf = fb_ctrs_t0.reference_perf;
> +
> + delta_reference = (u32)fb_ctrs_t1.reference -
> + (u32)fb_ctrs_t0.reference;
> + delta_delivered = (u32)fb_ctrs_t1.delivered -
> + (u32)fb_ctrs_t0.delivered;
Why (u32)? These registers can be 64bits and that's why cppc_perf_fb_ctrs
have 64b fields for reference and delivered counters.
Moreover, the integer math is incorrect. You can run into a scenario where
t1.ref/del < t0.ref/del, thus setting a negative number to u64! The likelihood
of this is very high especially when you throw away the higher 32bits.
To keep things simple, do something like below:
if (t1.reference <= t0.reference || t1.delivered <= t0.delivered) {
/* Atleast one of them should have overflowed */
return desired_perf;
}
else {
compute the delivered perf using the counters.
}
> +
> + /* Check to avoid divide-by zero */
> + if (delta_reference || delta_delivered)
> + delivered_perf = (reference_perf * delta_delivered) /
> + delta_reference;
> + else
> + delivered_perf = cpu->perf_ctrls.desired_perf;
> +
> + return cppc_cpufreq_perf_to_khz(cpu, delivered_perf);
> +}
> +
> +static unsigned int cppc_cpufreq_get_rate(unsigned int cpunum)
> +{
> + struct cppc_perf_fb_ctrs fb_ctrs_t0 = {0}, fb_ctrs_t1 = {0};
> + struct cppc_cpudata *cpu = all_cpu_data[cpunum];
> + int ret;
> +
> + ret = cppc_get_perf_ctrs(cpunum, &fb_ctrs_t0);
> + if (ret)
> + return ret;
> +
> + udelay(2); /* 2usec delay between sampling */
> +
> + ret = cppc_get_perf_ctrs(cpunum, &fb_ctrs_t1);
> + if (ret)
> + return ret;
> +
> + return cppc_get_rate_from_fbctrs(cpu, fb_ctrs_t0, fb_ctrs_t1);
> +}
> +
> static struct cpufreq_driver cppc_cpufreq_driver = {
> .flags = CPUFREQ_CONST_LOOPS,
> .verify = cppc_verify_policy,
> .target = cppc_cpufreq_set_target,
> + .get = cppc_cpufreq_get_rate,
> .init = cppc_cpufreq_cpu_init,
> .stop_cpu = cppc_cpufreq_stop_cpu,
> .name = "cppc_cpufreq",
