Re: [PATCH v2] sched/debug: Introduce per-CPU debugfs files

[Aaron Tomlin]

On Wed, Jul 29, 2026 at 09:25:20AM -0400, Aaron Tomlin wrote:
> On Tue, Jul 28, 2026 at 04:52:38PM -0400, Aaron Tomlin wrote:
> > Currently, accessing scheduler debugging details for a specific CPU
> > requires reading /sys/kernel/debug/sched/debug, which outputs
> > information for all online CPUs. When investigating a latency anomaly or
> > scheduling issue isolated to a specific CPU, accessing
> > /sys/kernel/debug/sched/cpu/cpu<N>/debug provides an immediate, targeted
> > view of that runqueue.
> > 
> > Add support for per-CPU debug files under:
> > /sys/kernel/debug/sched/cpu/cpu<N>/debug. Reading
> > /sys/kernel/debug/sched/cpu/cpu<N>/debug calls print_cpu() specifically
> > for CPU <N>, exposing CPU-specific runqueue details on demand. If the
> > target CPU is currently offline, reading its file returns -ENODEV.
> > 
> > Signed-off-by: Aaron Tomlin <atomlin@xxxxxxxxxxx>
> > ---
> > Changes since v1:
> > 
> >  - Reframed commit message motivation around targeted interactive
> >    debugging on large SMP topologies (Peter Zijlstra and Zhan Xusheng)
> > 
> >  - Gated sched_debug_cpu_show() with a cpu_online(cpu) check
> >    returning -ENODEV when target CPU is offline (Zhan Xusheng)
> > 
> >  - Linked to v1: https://lore.kernel.org/lkml/20260728020309.6169-1-atomlin@xxxxxxxxxxx/
> > ---
> >  kernel/sched/debug.c | 43 +++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 43 insertions(+)
> 
> Hi Peter, Ingo, Juri, Vincent,
> 
> Sashiko found [1] pre-existing issues, which are not related to this patch.
> Would you prefer that I investigate these concerns in this series?
> Thank you. 
> 
> [1]: https://sashiko.dev/#/patchset/20260728205238.18447-1-atomlin%40atomlin.com

Hi Peter, Ingo, Juri, Vincent,

These concerns appear valid.

I'll address them.

Kind regards,
-- 
Aaron Tomlin