Re: [PATCH V11 0/7] amd-pstate preferred core

Tor Vic
2023-11-30T14:35:36Z

On 11/29/23 07:54, Meng Li wrote:
> Hi all:
>
> The core frequency is subjected to the process variation in semiconductors.
> Not all cores are able to reach the maximum frequency respecting the
> infrastructure limits. Consequently, AMD has redefined the concept of
> maximum frequency of a part. This means that a fraction of cores can reach
> maximum frequency. To find the best process scheduling policy for a given
> scenario, OS needs to know the core ordering informed by the platform through
> highest performance capability register of the CPPC interface.
>
> Earlier implementations of amd-pstate preferred core only support a static
> core ranking and targeted performance. Now it has the ability to dynamically
> change the preferred core based on the workload and platform conditions and
> accounting for thermals and aging.
>
> Amd-pstate driver utilizes the functions and data structures provided by
> the ITMT architecture to enable the scheduler to favor scheduling on cores
> which can be get a higher frequency with lower voltage.
> We call it amd-pstate preferred core.
>
> Here sched_set_itmt_core_prio() is called to set priorities and
> sched_set_itmt_support() is called to enable ITMT feature.
> Amd-pstate driver uses the highest performance value to indicate
> the priority of CPU. The higher value has a higher priority.
>
> Amd-pstate driver will provide an initial core ordering at boot time.
> It relies on the CPPC interface to communicate the core ranking to the
> operating system and scheduler to make sure that OS is choosing the cores
> with highest performance firstly for scheduling the process. When amd-pstate
> driver receives a message with the highest performance change, it will
> update the core ranking.
>
> Changes from V10->V11:
> - cpufreq: amd-pstate:
> - - according Perry's commnts, I replace the string with str_enabled_disable().
>

Hi,

Using clang-17, I get the following warning:

----
drivers/cpufreq/amd-pstate.c:793:34: warning: variable 'cpudata' is
uninitialized when used here [-Wuninitialized]
793 | if ((!amd_pstate_prefcore) || (!cpudata->hw_prefcore))
| ^~~~~~~
drivers/cpufreq/amd-pstate.c:789:29: note: initialize the variable
'cpudata' to silence this warning
789 | struct amd_cpudata *cpudata;
| ^
| = NULL
1 warning generated.
----

Cheers,
Tor