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

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Message-Id: <20220912203722.205185-1-jeremy.linton@arm.com>
Date:   Mon, 12 Sep 2022 15:37:21 -0500
From:   Jeremy Linton <jeremy.linton@....com>
To:     linux-acpi@...r.kernel.org
Cc:     rafael@...nel.org, lenb@...nel.org, viresh.kumar@...aro.org,
        robert.moore@...el.com, punit.agrawal@...edance.com,
        lukasz.luba@....com, ionela.voinescu@....com,
        pierre.gondois@....com, linux-kernel@...r.kernel.org,
        devel@...ica.org, linux-pm@...r.kernel.org,
        Jeremy Linton <jeremy.linton@....com>
Subject: [PATCH v5 0/1] Disable FIE on machines with slow counters

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(-)

-- 
2.37.1