[PATCH v5 0/1] Disable FIE on machines with slow counters

From: Jeremy Linton
Date: Mon Sep 12 2022 - 16:37:41 EST


FIE assumes the delivered/relative perf registers are fast to read so
it goes ahead and hits them quite frequently. On a couple of Arm
platforms though they end up in PCC regions which require mailbox
handshaking with other parts of the platform.

This results in a lot of overhead in the cppc_fie task. As such lets
runtime disable FIE if we detect it enabled on one of those platforms.
Lastly, allow the user to override this decision via a module parameter.

v1->v2:
Apply Rafael's review comments.
Move the MODULE_PARAM into the ifdef
Fix compiler warning when ACPI_CPPC_LIB is disabled.
v2->v3:
Tristate the module param so FIE can be forced on/off
Bump pr_debug to pr_info if FIE is disabled due to PCC regions
Switch ACPI_CPPC_CPUFREQ_FIE off by default
v3->v4:
No functional change, resend due to email addr issues

v4->v5:
Minor whitespace, comment wording, if/case conversion
Drop the ACPI_CPPC_CPUFREQ_FIE disable config change added in v3

Jeremy Linton (1):
ACPI: CPPC: Disable FIE if registers in PCC regions

drivers/acpi/cppc_acpi.c | 42 ++++++++++++++++++++++++++++++++++
drivers/cpufreq/cppc_cpufreq.c | 25 ++++++++++++++++----
include/acpi/cppc_acpi.h | 5 ++++
3 files changed, 68 insertions(+), 4 deletions(-)

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2.37.1