The following commit has been merged into the perf/core branch of tip:

Commit-ID: 9f3de72a0c37005f897d69e4bdd59c25b8898447 Gitweb: https://git.kernel.org/tip/9f3de72a0c37005f897d69e4bdd59c25b8898447 Author: Kan Liang kan.liang@linux.intel.com AuthorDate: Tue, 19 Nov 2024 05:55:01 -08:00 Committer: Peter Zijlstra peterz@infradead.org CommitterDate: Mon, 02 Dec 2024 12:01:33 +01:00

perf/x86/intel/ds: Unconditionally drain PEBS DS when changing PEBS_DATA_CFG

The PEBS kernel warnings can still be observed with the below case.

when the below commands are running in parallel for a while.

while true; do perf record --no-buildid -a --intr-regs=AX \ -e cpu/event=0xd0,umask=0x81/pp \ -c 10003 -o /dev/null ./triad; done &

while true; do perf record -e 'cpu/mem-loads,ldlat=3/uP' -W -d -- ./dtlb done

The commit b752ea0c28e3 ("perf/x86/intel/ds: Flush PEBS DS when changing PEBS_DATA_CFG") intends to flush the entire PEBS buffer before the hardware is reprogrammed. However, it fails in the above case.

The first perf command utilizes the large PEBS, while the second perf command only utilizes a single PEBS. When the second perf event is added, only the n_pebs++. The intel_pmu_pebs_enable() is invoked after intel_pmu_pebs_add(). So the cpuc->n_pebs == cpuc->n_large_pebs check in the intel_pmu_drain_large_pebs() fails. The PEBS DS is not flushed. The new PEBS event should not be taken into account when flushing the existing PEBS DS.

The check is unnecessary here. Before the hardware is reprogrammed, all the stale records must be drained unconditionally.

For single PEBS or PEBS-vi-pt, the DS must be empty. The drain_pebs() can handle the empty case. There is no harm to unconditionally drain the PEBS DS.

Fixes: b752ea0c28e3 ("perf/x86/intel/ds: Flush PEBS DS when changing PEBS_DATA_CFG") Signed-off-by: Kan Liang kan.liang@linux.intel.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20241119135504.1463839-2-kan.liang@linux.intel.com --- arch/x86/events/intel/ds.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c index 8afc4ad..1a4b326 100644 --- a/arch/x86/events/intel/ds.c +++ b/arch/x86/events/intel/ds.c @@ -1489,7 +1489,7 @@ void intel_pmu_pebs_enable(struct perf_event *event) * hence we need to drain when changing said * size. */ - intel_pmu_drain_large_pebs(cpuc); + intel_pmu_drain_pebs_buffer(); adaptive_pebs_record_size_update(); wrmsrl(MSR_PEBS_DATA_CFG, pebs_data_cfg); cpuc->active_pebs_data_cfg = pebs_data_cfg;