Re: [PATCH v2 1/3] cppc_cpufreq: Return desired perf in ->get() if feedback counters are 0

Ionela Voinescu
2024-09-12T09:43:16Z

Hi,

On Thursday 12 Sep 2024 at 15:22:29 (+0800), Jie Zhan wrote:
> The CPPC performance feedback counters could return 0 when the target cpu
> is in a deep idle state, e.g. powered off, and those counters are not
> powered. In this case, cppc_cpufreq_get_rate() returns 0, and hence,
> cpufreq_online() gets a false error and doesn't generate a cpufreq policy,
> which happens in cpufreq_add_dev() when a new cpu device is added.
>
> Don't take it as an error and return the frequency corresponding to the
> desired perf when the feedback counters are 0.
>
> Fixes: 6a4fec4f6d30 ("cpufreq: cppc: cppc_cpufreq_get_rate() returns zero in all error cases.")
> Signed-off-by: Jie Zhan <zhanjie9@hisilicon.com>
> Reviewed-by: Zeng Heng <zengheng4@huawei.com>
> ---
> drivers/cpufreq/cppc_cpufreq.c | 19 +++++++++++++++++--
> 1 file changed, 17 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
> index bafa32dd375d..6aa3af56924b 100644
> --- a/drivers/cpufreq/cppc_cpufreq.c
> +++ b/drivers/cpufreq/cppc_cpufreq.c
> @@ -748,18 +748,33 @@ static unsigned int cppc_cpufreq_get_rate(unsigned int cpu)
>
> ret = cppc_get_perf_ctrs(cpu, &fb_ctrs_t0);
> if (ret)
> - return 0;
> + goto out_err;
>
> udelay(2); /* 2usec delay between sampling */
>
> ret = cppc_get_perf_ctrs(cpu, &fb_ctrs_t1);
> if (ret)
> - return 0;
> + goto out_err;
>
> delivered_perf = cppc_perf_from_fbctrs(cpu_data, &fb_ctrs_t0,
> &fb_ctrs_t1);
>
> return cppc_perf_to_khz(&cpu_data->perf_caps, delivered_perf);
> +
> +out_err:
> + /*
> + * Feedback counters could be 0 when cores are powered down.
> + * Take desired perf for reflecting frequency in this case.
> + */
> + if (ret == -EFAULT) {
> + ret = cppc_get_desired_perf(cpu, &delivered_perf);
> + if (ret)
> + return 0;
> +
> + return cppc_perf_to_khz(&cpu_data->perf_caps, delivered_perf);
> + }
> +
> + return 0;
> }

A possible (slimmer) alternative implementation for you to consider
(this merges patches 1 & 2):

diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
index bafa32dd375d..c16be9651a6f 100644
--- a/drivers/cpufreq/cppc_cpufreq.c
+++ b/drivers/cpufreq/cppc_cpufreq.c
@@ -118,6 +118,9 @@ static void cppc_scale_freq_workfn(struct kthread_work *work)

perf = cppc_perf_from_fbctrs(cpu_data, &cppc_fi->prev_perf_fb_ctrs,
&fb_ctrs);
+ if (!perf)
+ perf = cpu_data->perf_ctrls.desired_perf;
+
cppc_fi->prev_perf_fb_ctrs = fb_ctrs;

perf <<= SCHED_CAPACITY_SHIFT;
@@ -726,7 +729,7 @@ static int cppc_perf_from_fbctrs(struct cppc_cpudata *cpu_data,

/* Check to avoid divide-by zero and invalid delivered_perf */
if (!delta_reference || !delta_delivered)
- return cpu_data->perf_ctrls.desired_perf;
+ return 0;

return (reference_perf * delta_delivered) / delta_reference;
}
@@ -736,7 +739,7 @@ static unsigned int cppc_cpufreq_get_rate(unsigned int cpu)
struct cppc_perf_fb_ctrs fb_ctrs_t0 = {0}, fb_ctrs_t1 = {0};
struct cpufreq_policy *policy = cpufreq_cpu_get(cpu);
struct cppc_cpudata *cpu_data;
- u64 delivered_perf;
+ u64 delivered_perf = 0;
int ret;

if (!policy)
@@ -747,19 +750,22 @@ static unsigned int cppc_cpufreq_get_rate(unsigned int cpu)
cpufreq_cpu_put(policy);

ret = cppc_get_perf_ctrs(cpu, &fb_ctrs_t0);
- if (ret)
- return 0;
-
- udelay(2); /* 2usec delay between sampling */
-
- ret = cppc_get_perf_ctrs(cpu, &fb_ctrs_t1);
- if (ret)
- return 0;
+ if (!ret) {
+ udelay(2); /* 2usec delay between sampling */
+ ret = cppc_get_perf_ctrs(cpu, &fb_ctrs_t1);
+ }
+ if (!ret)
+ delivered_perf = cppc_perf_from_fbctrs(cpu_data, &fb_ctrs_t0,
+ &fb_ctrs_t1);
+ if ((ret == -EFAULT) || !delivered_perf) {
+ if (cppc_get_desired_perf(cpu, &delivered_perf))
+ delivered_perf = cpu_data->perf_ctrls.desired_perf;
+ }

- delivered_perf = cppc_perf_from_fbctrs(cpu_data, &fb_ctrs_t0,
- &fb_ctrs_t1);
+ if (delivered_perf)
+ return cppc_perf_to_khz(&cpu_data->perf_caps, delivered_perf);

- return cppc_perf_to_khz(&cpu_data->perf_caps, delivered_perf);
+ return 0;
}

disclaimer: not fully checked so likely not "production ready" code :)

Hope it helps,
Ionela.

>
> static int cppc_cpufreq_set_boost(struct cpufreq_policy *policy, int state)
> --
> 2.33.0
>