linux-kernel - [PATCH v2 0/1] Disable FIE on machines with slow counters

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Message-Id: <20220728221043.4161903-1-jeremy.linton@arm.com>
Date:   Thu, 28 Jul 2022 17:10:42 -0500
From:   Jeremy Linton <jeremy.linton@....com>
To:     linux-pm@...r.kernel.org
Cc:     rafael@...nel.org, lenb@...nel.org, viresh.kumar@...aro.org,
        robert.moore@...el.com, devel@...ica.org,
        linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jeremy Linton <jeremy.linton@....com>
Subject: [PATCH v2 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 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.
Also allow the user to manually disable it 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.

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

 drivers/acpi/cppc_acpi.c       | 41 ++++++++++++++++++++++++++++++++++
 drivers/cpufreq/cppc_cpufreq.c | 19 ++++++++++++----
 include/acpi/cppc_acpi.h       |  5 +++++
 3 files changed, 61 insertions(+), 4 deletions(-)

-- 
2.35.3