Re: [PATCHSET v2 sched_ext/for-7.3] sched_ext: Sub-scheduler and cid fixes

[Andrea Righi <arighi@nvidia.com>]

Hi Tejun,

On Tue, Jul 21, 2026 at 12:31:14PM -1000, Tejun Heo wrote:
> Hello,
> 
> v2: v1's 0003 only added NULL checks and, as Andrea and sashiko-bot pointed
>     out, left the cid tables readable while being filled and rewritten in
>     place. The new 0004 replaces it: each root enable builds a fresh table
>     set privately and publishes it with RCU once the layout is final. 0003
>     is a new trivial dead code removal. 0001-0002 are unchanged.
> 
> v1: https://lore.kernel.org/r/20260720082605.1451945-1-tj@kernel.org
> 
> A few fixes for the sub-scheduler and cid-form code on for-7.3.
> 
> - 0001 attributes a runnable stall to the scheduler that owns the DSQ the
>   task is stuck on rather than the task's owner, so a bypassing sub's task
>   parked on an ancestor's bypass DSQ blames the ancestor, not the sub.
> 
> - 0002 skips the default CPU selection while bypassing. The pick is discarded
>   by the bypass enqueue anyway, and it consults idle masks a scheduler doing
>   its own idle tracking leaves frozen.
> 
> - 0003 drops the unused scx_cpumask_to_cmask().
> 
> - 0004 ties the cid tables' lifetimes to the root sched: built privately on
>   enable, published with RCU once final, unpublished and RCU-freed on
>   disable.

I left a comment about PATCH 4/4 (purely doc stuff), overall looks good to me.
For the whole series:

Reviewed-by: Andrea Righi <arighi@nvidia.com>

Thanks,
-Andrea

> 
> Based on sched_ext/for-7.3 (b20dfde5ec54).
> 
> Tejun Heo (4):
>   sched_ext: Blame the DSQ's owning scheduler for a runnable stall
>   sched_ext: Skip the default CPU selection while bypassing
>   sched_ext: Drop unused scx_cpumask_to_cmask()
>   sched_ext: Build the cid tables privately and publish them with RCU
> 
> Git tree: git://git.kernel.org/pub/scm/linux/kernel/git/tj/sched_ext.git scx-sub-fixes-v2
> 
>  kernel/sched/ext/cid.c      | 279 ++++++++++++++++++++++++++------------------
>  kernel/sched/ext/cid.h      |  58 +++++----
>  kernel/sched/ext/ext.c      |  80 ++++++++++---
>  kernel/sched/ext/internal.h |   5 +-
>  kernel/sched/ext/sub.c      |  42 +++++--
>  5 files changed, 298 insertions(+), 166 deletions(-)
> 
> --
> tejun