On Mon, Oct 27, 2025 at 9:07 AM Ming Lei [off-list ref] wrote:

On Mon, Oct 20, 2025 at 08:46:46PM +0800, Ming Lei wrote:

quoted

When numgrps > nodes, group_cpus_evenly() can incorrectly assign CPUs
from different NUMA nodes to the same group due to the wrapping logic.
Then poor block IO performance is caused because of remote IO completion.
And it can be avoided completely in case of `numgrps > nodes` because
each numa node may includes more CPUs than group's.

The issue occurs when curgrp reaches last_grp and wraps to 0. This causes
CPUs from later-processed nodes to be added to groups that already contain
CPUs from earlier-processed nodes, violating NUMA locality.

Example with 8 NUMA nodes, 16 groups:
- Each node gets 2 groups allocated
- After processing nodes, curgrp reaches 16
- Wrapping to 0 causes CPUs from node N to be added to group 0 which
  already has CPUs from node 0

Fix this by adding find_next_node_group() helper that searches for the
next group (starting from 0) that already contains CPUs from the same
NUMA node. When wrapping is needed, use this helper instead of blindly
wrapping to 0, ensuring CPUs are only added to groups within the same
NUMA node.

Signed-off-by: Ming Lei <redacted>

Hello,

ping...

Hello,

Ping...

Thanks,
Ming