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 <[email protected]>
---
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);
--
2.39.2
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 <[email protected]>
I tested it and... it works.
Acked-by: Daniel Bristot de Oliveira <[email protected]>
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);