From: Jan H. Schönherr Date: Tue, 13 Jan 2026 20:34:46 +0000 (+0100) Subject: perf/core: Speed up kexec shutdown by avoiding unnecessary cross CPU calls X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=eebe6446ccb75ecb36cb145ab1cbc3db06cbc8d6;p=thirdparty%2Fkernel%2Flinux.git perf/core: Speed up kexec shutdown by avoiding unnecessary cross CPU calls There are typically a lot of PMUs registered, but in many cases only few of them have an event registered (like the "cpu" PMU in the presence of the watchdog). As the mutex is already held, it's safe to just check for existing events before doing the cross CPU call. This change saves tens of milliseconds from kexec time (perceived as steal time during a hypervisor host update), with <2ms remaining for this step in the shutdown. There might be additional potential for parallelization or we could just disable performance monitoring during the actual shutdown and be less graceful about it. Signed-off-by: Jan H. Schönherr Signed-off-by: David Woodhouse Signed-off-by: Peter Zijlstra (Intel) --- diff --git a/kernel/events/core.c b/kernel/events/core.c index 376fb07d869b8..101da5c1ab508 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -15066,7 +15066,8 @@ static void perf_event_exit_cpu_context(int cpu) ctx = &cpuctx->ctx; mutex_lock(&ctx->mutex); - smp_call_function_single(cpu, __perf_event_exit_context, ctx, 1); + if (ctx->nr_events) + smp_call_function_single(cpu, __perf_event_exit_context, ctx, 1); cpuctx->online = 0; mutex_unlock(&ctx->mutex); mutex_unlock(&pmus_lock);