Re: [PATCH] cpufreq/cppc: changing highest_perf to nominal_perf in cppc_cpufreq_cpu_init()

From: Pierre Gondois
Date: Fri May 03 2024 - 10:19:21 EST


Hello Liwei,
The change itself seems ok, but I'm not sure I understand what the
issue is exactly.

On 4/29/24 12:49, Viresh Kumar wrote:
CC'ing few folks who are working with the driver.

On 28-04-24, 17:28, liwei wrote:
When turning on turbo, if frequency configuration takes effect slowly,
the updated policy->cur may be equal to the frequency configured in
governor->limits(), performance governor will not adjust the frequency,
configured frequency will remain at turbo-freq.

Simplified call stack looks as follows:
cpufreq_register_driver(&cppc_cpufreq_driver)
...
cppc_cpufreq_cpu_init()
cppc_get_perf_caps()
policy->max = cppc_perf_to_khz(caps, caps->nominal_perf)
cppc_set_perf(highest_perf) // set highest_perf
policy->cur = cpufreq_driver->get() // if cur == policy->max

During the driver initialization, we have:
cppc_cpufreq_cpu_init()
\-policy->max = cppc_perf_to_khz(caps, caps->nominal_perf)
\-policy->cur = cppc_perf_to_khz(caps, caps->highest_perf);
\-cpu_data->perf_ctrls.desired_perf = caps->highest_perf;
\-cppc_set_perf(cpu, &cpu_data->perf_ctrls); // set freq to highest_perf
so here:
policy->max = nominal_freq
policy->cur = highest_freq


And then for the cpufreq framework:
cpufreq_online()
// IIUC there is some delay here, so policy->cur = nominal_freq ?
// i.e. the freq. was requested to change to the highest_freq,
// but the change is not effective yet ?
\-policy->cur = cpufreq_driver->get(policy->cpu);
\-cpufreq_init_policy()
\-cpufreq_set_policy()
\-cpufreq_start_governor()
\-cpufreq_verify_current_freq()
\-new_freq = cpufreq_driver->get(policy->cpu); // new_freq = nominal_freq ?
\-if (policy->cur != new_freq)
\- cpufreq_out_of_sync()
\- policy->cur = new_freq;
\-cpufreq_start_governor()
\-cpufreq_gov_performance_limits()
\-__cpufreq_driver_target(target_freq=policy->max) // with policy->max = nominal_freq ?
\-if (target_freq == policy->cur)
\- // do nothing

I am not sure I understand when you are turning the turbo on with:
# echo 1 > /sys/devices/system/cpu/cpufreq/boost

Or do you mean that turbo is available but not turned on ?


Regards,
Pierre

cpufreq_init_policy()
...
cpufreq_start_governor() // governor: performance
new_freq = cpufreq_driver->get() // if new_freq == policy->max
if (policy->cur != new_freq)
cpufreq_out_of_sync(policy, new_freq)
...
policy->cur = new_freq
...
policy->governor->limits()
__cpufreq_driver_target(policy->max)
if (policy->cur==target)
// generate error, keep set highest_perf
ret
cppc_set_perf(target)

Fix this by changing highest_perf to nominal_perf in cppc_cpufreq_cpu_init().

Fixes: 5477fb3bd1e8 ("ACPI / CPPC: Add a CPUFreq driver for use with CPPC")
Signed-off-by: liwei <liwei728@xxxxxxxxxx>
---
drivers/cpufreq/cppc_cpufreq.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
index 64420d9cfd1e..db04a82b8a97 100644
--- a/drivers/cpufreq/cppc_cpufreq.c
+++ b/drivers/cpufreq/cppc_cpufreq.c
@@ -669,14 +669,14 @@ static int cppc_cpufreq_cpu_init(struct cpufreq_policy *policy)
if (caps->highest_perf > caps->nominal_perf)
boost_supported = true;
- /* Set policy->cur to max now. The governors will adjust later. */
- policy->cur = cppc_perf_to_khz(caps, caps->highest_perf);
- cpu_data->perf_ctrls.desired_perf = caps->highest_perf;
+ /* Set policy->cur to norm now. */
+ policy->cur = cppc_perf_to_khz(caps, caps->nominal_perf);
+ cpu_data->perf_ctrls.desired_perf = caps->nominal_perf;
ret = cppc_set_perf(cpu, &cpu_data->perf_ctrls);
if (ret) {
pr_debug("Err setting perf value:%d on CPU:%d. ret:%d\n",
- caps->highest_perf, cpu, ret);
+ caps->nominal_perf, cpu, ret);
goto out;
}
--
2.25.1