perf/x86/intel: Add a check for dynamic constraints

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The current event scheduler has a limit. If the counter constraint of an
event is not a subset of any other counter constraint with an equal or
higher weight. The counters may not be fully utilized.

To workaround it, the commit bc1738f6ee ("perf, x86: Fix event
scheduler for constraints with overlapping counters") introduced an
overlap flag, which is hardcoded to the event constraint that may
trigger the limit. It only works for static constraints.

Many features on and after Intel PMON v6 require dynamic constraints. An
event constraint is decided by both static and dynamic constraints at
runtime. See commit 4dfe3232cc ("perf/x86: Add dynamic constraint").
The dynamic constraints are from CPUID enumeration. It's impossible to
hardcode it in advance. It's not practical to set the overlap flag to all
events. It's harmful to the scheduler.

For the existing Intel platforms, the dynamic constraints don't trigger
the limit. A real fix is not required.

However, for virtualization, VMM may give a weird CPUID enumeration to a
guest. It's impossible to indicate what the weird enumeration is. A
check is introduced, which can list the possible breaks if a weird
enumeration is used.

Check the dynamic constraints enumerated for normal, branch counters
logging, and auto-counter reload.
Check both PEBS and non-PEBS constratins.

Closes: https://lore.kernel.org/lkml/20250416195610.GC38216@noisy.programming.kicks-ass.net/
Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20250512175542.2000708-1-kan.liang@linux.intel.com

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Kan Liang 2025-05-12 10:55:42 -07:00 • committed by Peter Zijlstra

parent bb5f13df3c

commit bd24f9beed

1 changed files with 148 additions and 8 deletions

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arch/x86/events/intel/core.c

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