Re: [PATCH 2/3] rbtree: update augmented data on the way down in rb_add_augmented_cached()

[Yiwei Lin]

On 2026/09/29 05:37, Peter Zijlstra wrote:
> This builds and boot, so it must be perfect, right ;-)
>
> Assisted-by: Brain
> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>

Right, thanks.

If you're fine with me carrying it, I can take it into v2 with and
derive ->merge() from the same RB_AUG() list, so
rb_add_augmented_cached() folds the new node into its ancestors in
the one pass down instead of the ->propagate() round trip.

One thing I am aware here:  RB_AUG()'s cmp only
expresses "pick one of the two", so min/max style aggregates; a sum or
a count (subtree size, total weight) can't be written, where the old
RBCOMPUTE could do anything.  Nobody in-tree needs that today, so it might
be acceptable as is, but it's a regression in generality for the same
price:

        RB_AUG(val, aug, fold)  /* _val = fold(_val, child->aug) */

keeps the register-local recompute exactly as it is, drops RB_MIN /
RB_MAX in favour of the existing min()/max(), and a sum is just
"a + b".  For sched that's min, max and a wrapping-safe min for
min_vruntime. Do you think this can be accepted as is, or should I try
to make it more general?


Thanks,
Yiwei