Messages in this thread | | | From | Punit Agrawal <> | Subject | Re: [PATCH v2 1/1] ACPI: CPPC: Disable FIE if registers in PCC regions | Date | Fri, 29 Jul 2022 13:59:43 +0100 |
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Hi Jeremy,
One comment / query below.
Jeremy Linton <jeremy.linton@arm.com> writes:
> PCC regions utilize a mailbox to set/retrieve register values used by > the CPPC code. This is fine as long as the operations are > infrequent. With the FIE code enabled though the overhead can range > from 2-11% of system CPU overhead (ex: as measured by top) on Arm > based machines. > > So, before enabling FIE assure none of the registers used by > cppc_get_perf_ctrs() are in the PCC region. Furthermore lets also > enable a module parameter which can also disable it at boot or module > reload. > > Signed-off-by: Jeremy Linton <jeremy.linton@arm.com> > --- > 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(-) >
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> diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c > index 24eaf0ec344d..ed607e27d6bb 100644 > --- a/drivers/cpufreq/cppc_cpufreq.c > +++ b/drivers/cpufreq/cppc_cpufreq.c
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> @@ -229,7 +233,12 @@ static void __init cppc_freq_invariance_init(void) > }; > int ret; > > - if (cppc_cpufreq_driver.get == hisi_cppc_cpufreq_get_rate) > + if (cppc_perf_ctrs_in_pcc()) { > + pr_debug("FIE not enabled on systems with registers in PCC\n");
The message should probably be promoted to a pr_info() and exposed as part of the kernel logs. It is a change in the default behaviour we've had until now. The message will provide some hint about why it was disabled.
Thoughts?
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