From: Peter Zijlstra peterz@infradead.org
commit 90c91dfb86d0ff545bd329d3ddd72c147e2ae198 upstream.
Kan and Andi reported that we fail to kill rotation when the flexible events go empty, but the context does not. XXX moar
Fixes: fd7d55172d1e ("perf/cgroups: Don't rotate events for cgroups unnecessarily") Reported-by: Andi Kleen ak@linux.intel.com Reported-by: Kan Liang kan.liang@linux.intel.com Tested-by: Kan Liang kan.liang@linux.intel.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Link: https://lkml.kernel.org/r/20200305123851.GX2596@hirez.programming.kicks-ass.... Cc: Robin Murphy robin.murphy@arm.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- kernel/events/core.c | 20 ++++++++++++++------ 1 file changed, 14 insertions(+), 6 deletions(-)
--- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -2171,6 +2171,7 @@ __perf_remove_from_context(struct perf_e
if (!ctx->nr_events && ctx->is_active) { ctx->is_active = 0; + ctx->rotate_necessary = 0; if (ctx->task) { WARN_ON_ONCE(cpuctx->task_ctx != ctx); cpuctx->task_ctx = NULL; @@ -3047,12 +3048,6 @@ static void ctx_sched_out(struct perf_ev if (!ctx->nr_active || !(is_active & EVENT_ALL)) return;
- /* - * If we had been multiplexing, no rotations are necessary, now no events - * are active. - */ - ctx->rotate_necessary = 0; - perf_pmu_disable(ctx->pmu); if (is_active & EVENT_PINNED) { list_for_each_entry_safe(event, tmp, &ctx->pinned_active, active_list) @@ -3062,6 +3057,13 @@ static void ctx_sched_out(struct perf_ev if (is_active & EVENT_FLEXIBLE) { list_for_each_entry_safe(event, tmp, &ctx->flexible_active, active_list) group_sched_out(event, cpuctx, ctx); + + /* + * Since we cleared EVENT_FLEXIBLE, also clear + * rotate_necessary, is will be reset by + * ctx_flexible_sched_in() when needed. + */ + ctx->rotate_necessary = 0; } perf_pmu_enable(ctx->pmu); } @@ -3800,6 +3802,12 @@ ctx_event_to_rotate(struct perf_event_co typeof(*event), group_node); }
+ /* + * Unconditionally clear rotate_necessary; if ctx_flexible_sched_in() + * finds there are unschedulable events, it will set it again. + */ + ctx->rotate_necessary = 0; + return event; }