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Documentation: amd-pstate: add driver working mode introduction 

Introduce the `amd_pstate` driver new working mode with
`amd_pstate=passive` added to kernel command line.
If there is no passive mode enabled by user, amd_pstate driver will be
disabled by default for now.

Acked-by: Huang Rui <ray.huang@amd.com>
Reviewed-by: Gautham R. Shenoy <gautham.shenoy@amd.com>
Tested-by: Wyes Karny <wyes.karny@amd.com>
Signed-off-by: Perry Yuan <Perry.Yuan@amd.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
This commit is contained in:
Perry Yuan 2022-11-17 15:35:40 +08:00 committed by Rafael J. Wysocki
parent 202e683df3
commit 8a2cbf72a4
1 changed files with 11 additions and 15 deletions
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26
Documentation/admin-guide/pm/amd-pstate.rst
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@ -283,23 +283,19 @@ efficiency frequency management method on AMD processors.
Kernel Module Options for ``amd-pstate``
=========================================
.. _shared_mem:
Passive Mode
------------
``shared_mem``
Use a module param (shared_mem) to enable related processors manually with
**amd_pstate.shared_mem=1**.
Due to the performance issue on the processors with `Shared Memory Support
<perf_cap_>`_, we disable it presently and will re-enable this by default
once we address performance issue with this solution.
``amd_pstate=passive``
To check whether the current processor is using `Full MSR Support <perf_cap_>`_
or `Shared Memory Support <perf_cap_>`_ : ::
ray@hr-test1:~$ lscpu | grep cppc
Flags: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt pdpe1gb rdtscp lm constant_tsc rep_good nopl nonstop_tsc cpuid extd_apicid aperfmperf rapl pni pclmulqdq monitor ssse3 fma cx16 sse4_1 sse4_2 x2apic movbe popcnt aes xsave avx f16c rdrand lahf_lm cmp_legacy svm extapic cr8_legacy abm sse4a misalignsse 3dnowprefetch osvw ibs skinit wdt tce topoext perfctr_core perfctr_nb bpext perfctr_llc mwaitx cpb cat_l3 cdp_l3 hw_pstate ssbd mba ibrs ibpb stibp vmmcall fsgsbase bmi1 avx2 smep bmi2 erms invpcid cqm rdt_a rdseed adx smap clflushopt clwb sha_ni xsaveopt xsavec xgetbv1 xsaves cqm_llc cqm_occup_llc cqm_mbm_total cqm_mbm_local clzero irperf xsaveerptr rdpru wbnoinvd cppc arat npt lbrv svm_lock nrip_save tsc_scale vmcb_clean flushbyasid decodeassists pausefilter pfthreshold avic v_vmsave_vmload vgif v_spec_ctrl umip pku ospke vaes vpclmulqdq rdpid overflow_recov succor smca fsrm
If the CPU flags have ``cppc``, then this processor supports `Full MSR Support
<perf_cap_>`_. Otherwise, it supports `Shared Memory Support <perf_cap_>`_.
It will be enabled if the ``amd_pstate=passive`` is passed to the kernel in the command line.
In this mode, ``amd_pstate`` driver software specifies a desired QoS target in the CPPC
performance scale as a relative number. This can be expressed as percentage of nominal
performance (infrastructure max). Below the nominal sustained performance level,
desired performance expresses the average performance level of the processor subject
to the Performance Reduction Tolerance register. Above the nominal performance level,
processor must provide at least nominal performance requested and go higher if current
operating conditions allow.
``cpupower`` tool support for ``amd-pstate``