From e89d120c4b720e232cc6a94f0fcbd59c15d41489 Mon Sep 17 00:00:00 2001 From: Ionela Voinescu Date: Fri, 19 Aug 2022 11:30:50 +0100 Subject: 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 Reviewed-by: Catalin Marinas Cc: Catalin Marinas Cc: Will Deacon Cc: James Morse Link: https://lore.kernel.org/r/20220819103050.24211-1-ionela.voinescu@arm.com Signed-off-by: Will Deacon --- arch/arm64/kernel/cpufeature.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) (limited to 'arch/arm64/kernel/cpufeature.c') diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c index 907401e4fffb..af4de817d712 100644 --- a/arch/arm64/kernel/cpufeature.c +++ b/arch/arm64/kernel/cpufeature.c @@ -1870,7 +1870,10 @@ static void cpu_amu_enable(struct arm64_cpu_capabilities const *cap) pr_info("detected CPU%d: Activity Monitors Unit (AMU)\n", smp_processor_id()); cpumask_set_cpu(smp_processor_id(), &amu_cpus); - update_freq_counters_refs(); + + /* 0 reference values signal broken/disabled counters */ + if (!this_cpu_has_cap(ARM64_WORKAROUND_2457168)) + update_freq_counters_refs(); } } -- cgit v1.2.3-59-g8ed1b