trace/hwlat: Do not start per-cpu thread if it is already running

The hwlatd tracer will end up starting multiple per-cpu threads with the following script: #!/bin/sh cd /sys/kernel/debug/tracing echo 0 > tracing_on echo hwlat > current_tracer echo per-cpu > hwlat_detector/mode echo 100000 > hwlat_detector/width echo 200000 > hwlat_detector/window echo 1 > tracing_on To fix the issue, check if the hwlatd thread for the cpu is already running, before starting a new one. Along with the previous patch, this avoids running multiple instances of the same CPU thread on the system. Link: https://lore.kernel.org/all/20230302113654.2984709-1-tero.kristo@linux.intel.com/ Link: https://lkml.kernel.org/r/20230310100451.3948583-3-tero.kristo@linux.intel.com

Tero Kristo committed 3 years ago

Commit 08697bc1 parent 4c42f5f1 file · +4 −0Browse files

Unified · Split

kernel/trace/trace_hwlat.c+4−0

@@ -492,6 +492,10 @@ static int start_cpu_kthread(unsigned int cpu) · 491 unmodified lines
492	492	{
493	493	struct task_struct *kthread;
494	494
	495	+ /* Do not start a new hwlatd thread if it is already running */
	496	+ if (per_cpu(hwlat_per_cpu_data, cpu).kthread)
	497	+ return 0;
	498	+
495	499	kthread = kthread_run_on_cpu(kthread_fn, NULL, cpu, "hwlatd/%u");
496	500	if (IS_ERR(kthread)) {
497	501	pr_err(BANNER "could not start sampling thread\n");