| Message ID | 20230316144535.1004952-1-costa.shul@redhat.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 71c7a30442b724717a30d5e7d1662ba4904eb3d4 |
| Headers | show |
| Series | tracing/hwlat: Replace sched_setaffinity with set_cpus_allowed_ptr | expand |
On 3/16/23 15:45, Costa Shulyupin wrote: > There is a problem with the behavior of hwlat in a container, > resulting in incorrect output. A warning message is generated: > "cpumask changed while in round-robin mode, switching to mode none", > and the tracing_cpumask is ignored. This issue arises because > the kernel thread, hwlatd, is not a part of the container, and > the function sched_setaffinity is unable to locate it using its PID. > Additionally, the task_struct of hwlatd is already known. > Ultimately, the function set_cpus_allowed_ptr achieves > the same outcome as sched_setaffinity, but employs task_struct > instead of PID. > > Test case: > > # cd /sys/kernel/tracing > # echo 0 > tracing_on > # echo round-robin > hwlat_detector/mode > # echo hwlat > current_tracer > # unshare --fork --pid bash -c 'echo 1 > tracing_on' > # dmesg -c > > Actual behavior: > > [573502.809060] hwlat_detector: cpumask changed while in round-robin mode, switching to mode none > > Signed-off-by: Costa Shulyupin <costa.shul@redhat.com> I tested it and... it works. Acked-by: Daniel Bristot de Oliveira <bristot@kernel.org> Thanks -- Daniel > --- > kernel/trace/trace_hwlat.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/kernel/trace/trace_hwlat.c b/kernel/trace/trace_hwlat.c > index d440ddd5fd8b..444dfc31f258 100644 > --- a/kernel/trace/trace_hwlat.c > +++ b/kernel/trace/trace_hwlat.c > @@ -339,7 +339,7 @@ static void move_to_next_cpu(void) > cpumask_clear(current_mask); > cpumask_set_cpu(next_cpu, current_mask); > > - sched_setaffinity(0, current_mask); > + set_cpus_allowed_ptr(current, current_mask); > return; > > change_mode: > @@ -446,7 +446,7 @@ static int start_single_kthread(struct trace_array *tr) > > } > > - sched_setaffinity(kthread->pid, current_mask); > + set_cpus_allowed_ptr(kthread, current_mask); > > kdata->kthread = kthread; > wake_up_process(kthread);
diff --git a/kernel/trace/trace_hwlat.c b/kernel/trace/trace_hwlat.c index d440ddd5fd8b..444dfc31f258 100644 --- a/kernel/trace/trace_hwlat.c +++ b/kernel/trace/trace_hwlat.c @@ -339,7 +339,7 @@ static void move_to_next_cpu(void) cpumask_clear(current_mask); cpumask_set_cpu(next_cpu, current_mask); - sched_setaffinity(0, current_mask); + set_cpus_allowed_ptr(current, current_mask); return; change_mode: @@ -446,7 +446,7 @@ static int start_single_kthread(struct trace_array *tr) } - sched_setaffinity(kthread->pid, current_mask); + set_cpus_allowed_ptr(kthread, current_mask); kdata->kthread = kthread; wake_up_process(kthread);
There is a problem with the behavior of hwlat in a container, resulting in incorrect output. A warning message is generated: "cpumask changed while in round-robin mode, switching to mode none", and the tracing_cpumask is ignored. This issue arises because the kernel thread, hwlatd, is not a part of the container, and the function sched_setaffinity is unable to locate it using its PID. Additionally, the task_struct of hwlatd is already known. Ultimately, the function set_cpus_allowed_ptr achieves the same outcome as sched_setaffinity, but employs task_struct instead of PID. Test case: # cd /sys/kernel/tracing # echo 0 > tracing_on # echo round-robin > hwlat_detector/mode # echo hwlat > current_tracer # unshare --fork --pid bash -c 'echo 1 > tracing_on' # dmesg -c Actual behavior: [573502.809060] hwlat_detector: cpumask changed while in round-robin mode, switching to mode none Signed-off-by: Costa Shulyupin <costa.shul@redhat.com> --- kernel/trace/trace_hwlat.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)