Commit ffc6aabf authored by Kan Liang's avatar Kan Liang Committed by Yunying Sun
Browse files

perf/x86/intel: Add a quirk for the calculation of the number of counters on Alder Lake

mainline inclusion
from mainline-v5.17-rc2
commit 7fa981ca
category: feature
feature: SRF core PMU support
bugzilla: https://gitee.com/openeuler/intel-kernel/issues/I8RWG5
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7fa981cad216e9f64f49e22112f610c0bfed91bc



Intel-SIG: commit 7fa981ca perf/x86/intel: Add a quirk for the calculation of the number of counters on Alder Lake
Backport as a dependency for Sierra Forrest core PMU support.

-------------------------------------

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: ee72a94e ("perf/x86/intel: Fix fixed counter check warning for some Alder Lake")
Reported-by: default avatarDamjan Marion (damarion) <damarion@cisco.com>
Reported-by: default avatarChan Edison <edison_chan_gz@hotmail.com>
Signed-off-by: default avatarKan Liang <kan.liang@linux.intel.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: default avatarDamjan 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


Signed-off-by: default avatarYunying Sun <yunying.sun@intel.com>
parent f734c889
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