From: Kan Liang kan.liang@linux.intel.com
commit 7fa981cad216e9f64f49e22112f610c0bfed91bc upstream.
For some Alder Lake machine with all E-cores disabled in a BIOS, the below warning may be triggered.
[ 2.010766] hw perf events fixed 5 > max(4), clipping!
Current perf code relies on the CPUID leaf 0xA and leaf 7.EDX[15] to calculate the number of the counters and follow the below assumption.
For a hybrid configuration, the leaf 7.EDX[15] (X86_FEATURE_HYBRID_CPU) is set. The leaf 0xA only enumerate the common counters. Linux perf has to manually add the extra GP counters and fixed counters for P-cores. For a non-hybrid configuration, the X86_FEATURE_HYBRID_CPU should not be set. The leaf 0xA enumerates all counters.
However, that's not the case when all E-cores are disabled in a BIOS. Although there are only P-cores in the system, the leaf 7.EDX[15] (X86_FEATURE_HYBRID_CPU) is still set. But the leaf 0xA is updated to enumerate all counters of P-cores. The inconsistency triggers the warning.
Several software ways were considered to handle the inconsistency. - Drop the leaf 0xA and leaf 7.EDX[15] CPUID enumeration support. Hardcode the number of counters. This solution may be a problem for virtualization. A hypervisor cannot control the number of counters in a Linux guest via changing the guest CPUID enumeration anymore. - Find another CPUID bit that is also updated with E-cores disabled. There may be a problem in the virtualization environment too. Because a hypervisor may disable the feature/CPUID bit. - The P-cores have a maximum of 8 GP counters and 4 fixed counters on ADL. The maximum number can be used to detect the case. This solution is implemented in this patch.
Fixes: ee72a94ea4a6 ("perf/x86/intel: Fix fixed counter check warning for some Alder Lake") Reported-by: Damjan Marion (damarion) damarion@cisco.com Reported-by: Chan Edison edison_chan_gz@hotmail.com Signed-off-by: Kan Liang kan.liang@linux.intel.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Tested-by: Damjan Marion (damarion) damarion@cisco.com Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/1641925238-149288-1-git-send-email-kan.liang@linux... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/events/intel/core.c | 13 +++++++++++++ 1 file changed, 13 insertions(+)
--- a/arch/x86/events/intel/core.c +++ b/arch/x86/events/intel/core.c @@ -6242,6 +6242,19 @@ __init int intel_pmu_init(void) pmu->num_counters = x86_pmu.num_counters; pmu->num_counters_fixed = x86_pmu.num_counters_fixed; } + + /* + * Quirk: For some Alder Lake machine, when all E-cores are disabled in + * a BIOS, the leaf 0xA will enumerate all counters of P-cores. However, + * the X86_FEATURE_HYBRID_CPU is still set. The above codes will + * mistakenly add extra counters for P-cores. Correct the number of + * counters here. + */ + if ((pmu->num_counters > 8) || (pmu->num_counters_fixed > 4)) { + pmu->num_counters = x86_pmu.num_counters; + pmu->num_counters_fixed = x86_pmu.num_counters_fixed; + } + pmu->max_pebs_events = min_t(unsigned, MAX_PEBS_EVENTS, pmu->num_counters); pmu->unconstrained = (struct event_constraint) __EVENT_CONSTRAINT(0, (1ULL << pmu->num_counters) - 1,