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authorKan Liang <kan.liang@linux.intel.com>2022-01-11 19:20:38 +0100
committerPeter Zijlstra <peterz@infradead.org>2022-01-18 12:09:47 +0100
commit7fa981cad216e9f64f49e22112f610c0bfed91bc (patch)
treea0a430cdeed9f31472f411e1b9dbe5de4b79ab26 /ipc
parentperf: Fix perf_event_read_local() time (diff)
downloadlinux-7fa981cad216e9f64f49e22112f610c0bfed91bc.tar.xz
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perf/x86/intel: Add a quirk for the calculation of the number of counters on Alder Lake
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.intel.com
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