perf/x86/amd/uncore: Remove redundant event slot scan

amd_uncore_add() first checks the slot recorded in event->hw.idx. If
that misses, it scans ctx->events[] for the event before looking for a
free slot.

Perf serializes ->add() and ->del() for an event. Initialization sets
idx to -1. A successful ->add() claims a slot and records its index
before returning, while ->del() clears the slot before resetting idx.
CPU context migration follows the same delete/add sequence.

Thus an installed event can only reside at the recorded index. If the
direct check misses, the event is not present in ctx->events[].

Remove the redundant scan. This avoids walking all counters before each
new slot search after multiplexing has scheduled an event out.

On a host running a production workload in the Meta fleet, amd_uncore_add()
was called 56,575 times per second from mux rotation. Its 16-counter DF PMU
makes each failed search scan 16 pointers across two cache lines.

Signed-off-by: Usama Arif <usama.arif@linux.dev>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Sandipan Das <sandipan.das@amd.com>
Link: https://patch.msgid.link/20260921153108.2713179-2-usama.arif@linux.dev

0 files changed, 0 insertions, 0 deletions