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
