linux/Documentation/arm64
Ionela Voinescu e89d120c4b arm64: errata: add detection for AMEVCNTR01 incrementing incorrectly
The AMU counter AMEVCNTR01 (constant counter) should increment at the same
rate as the system counter. On affected Cortex-A510 cores, AMEVCNTR01
increments incorrectly giving a significantly higher output value. This
results in inaccurate task scheduler utilization tracking and incorrect
feedback on CPU frequency.

Work around this problem by returning 0 when reading the affected counter
in key locations that results in disabling all users of this counter from
using it either for frequency invariance or as FFH reference counter. This
effect is the same to firmware disabling affected counters.

Details on how the two features are affected by this erratum:

 - AMU counters will not be used for frequency invariance for affected
   CPUs and CPUs in the same cpufreq policy. AMUs can still be used for
   frequency invariance for unaffected CPUs in the system. Although
   unlikely, if no alternative method can be found to support frequency
   invariance for affected CPUs (cpufreq based or solution based on
   platform counters) frequency invariance will be disabled. Please check
   the chapter on frequency invariance at
   Documentation/scheduler/sched-capacity.rst for details of its effect.

 - Given that FFH can be used to fetch either the core or constant counter
   values, restrictions are lifted regarding any of these counters
   returning a valid (!0) value. Therefore FFH is considered supported
   if there is a least one CPU that support AMUs, independent of any
   counters being disabled or affected by this erratum. Clarifying
   comments are now added to the cpc_ffh_supported(), cpu_read_constcnt()
   and cpu_read_corecnt() functions.

The above is achieved through adding a new erratum: ARM64_ERRATUM_2457168.

Signed-off-by: Ionela Voinescu <ionela.voinescu@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: James Morse <james.morse@arm.com>
Link: https://lore.kernel.org/r/20220819103050.24211-1-ionela.voinescu@arm.com
Signed-off-by: Will Deacon <will@kernel.org>
2022-08-23 11:06:48 +01:00
..
acpi_object_usage.rst Documentation: arm64/acpi : clarify arm64 support of IBFT 2021-03-22 12:43:20 +00:00
amu.rst Documentation: Chinese translation of Documentation/arm64/amu.rst 2020-09-28 15:24:24 -06:00
arm-acpi.rst arm64: Replace HTTP links with HTTPS ones 2020-07-23 14:04:37 -06:00
asymmetric-32bit.rst Documentation: arm64: describe asymmetric 32-bit support 2021-08-20 12:33:07 +02:00
booting.rst arm64: document the boot requirements for MTE 2022-04-25 17:15:04 +01:00
cpu-feature-registers.rst arm64: Add HWCAP advertising FEAT_WFXT 2022-04-20 13:24:44 +01:00
elf_hwcaps.rst docs/arm64: elf_hwcaps: unify newlines in HWCAP lists 2022-08-23 10:38:39 +01:00
features.rst docs: archis: add a per-architecture features list 2020-12-03 15:10:15 -07:00
hugetlbpage.rst Documentation: Chinese translation of Documentation/arm64/hugetlbpage.rst 2020-10-21 15:15:17 -06:00
index.rst arm64/sme: Provide ABI documentation for SME 2022-04-22 18:50:39 +01:00
kasan-offsets.sh arm64: mm: extend linear region for 52-bit VA configurations 2020-11-09 17:15:37 +00:00
legacy_instructions.rst docs: arm64: convert docs to ReST and rename to .rst 2019-06-14 14:20:27 -06:00
memory-tagging-extension.rst elf: Fix the arm64 MTE ELF segment name and value 2022-04-28 11:37:06 +01:00
memory.rst Documentation/arm64: update memory layout table. 2022-06-23 18:35:40 +01:00
perf.rst Documentation: arm64: Document PMU counters access from userspace 2021-12-14 11:41:19 +00:00
pointer-authentication.rst arm64: update PAC description for kernel 2021-12-02 10:13:35 +00:00
silicon-errata.rst arm64: errata: add detection for AMEVCNTR01 incrementing incorrectly 2022-08-23 11:06:48 +01:00
sme.rst arm64/sme: Fix SVE/SME typo in ABI documentation 2022-06-08 18:38:31 +01:00
sve.rst arm64/sme: Provide ABI documentation for SME 2022-04-22 18:50:39 +01:00
tagged-address-abi.rst docs/arm64: delete a space from tagged-address-abi 2021-12-14 19:01:37 +00:00
tagged-pointers.rst arm64: expose FAR_EL1 tag bits in siginfo 2020-11-23 18:17:39 +00:00