Re: [PATCH v3 8/8] sched/fair: Simplify SIS_UTIL handling in select_idle_cpu()

[Chen, Yu C]

On 1/20/2026 7:32 PM, K Prateek Nayak wrote:
> Use the "sd_llc" passed to select_idle_cpu() to obtain the
> "sd_llc_shared" instead of dereferencing the per-CPU variable.
>
> Since "sd->shared" is always reclaimed at the same time as "sd" via
> call_rcu() and update_top_cache_domain() always ensures a valid
> "sd->shared" assignment when "sd_llc" is present, "sd_llc->shared" can
> always be dereferenced without needing an additional check.
>
> While at it move the cpumask_and() operation after the SIS_UTIL bailout
> check to avoid unnecessarily computing the cpumask.
>
> Signed-off-by: K Prateek Nayak <kprateek.nayak@xxxxxxx>
> ---

Reviewed-by: Chen Yu <yu.c.chen@xxxxxxxxx>

I ran netperf, schbench, hackbench, stress-ng-context,
and stream on a platform with 384 CPUs and 6 nodes, and no
significant differences were observed. (Netperf is of the
greatest interest because SIS_UTIL had a substantial impact
on netperf when it was first introduced.) I suppose
sched/topology: Switch to assigning "sd->shared" from s_data
will have a new version, I'll look at it when it is posted.

netperf
                          baseline                    llc
Hmean-96pairs     119.86 (   0.00%)      122.21 (   1.96%)
Hmean-192pairs    56.48  (   0.00%)       57.37  (   1.57%)
Hmean-288pairs    78.27  (   0.00%)       78.21  (  -0.08%)
Hmean-384pairs    62.69  (   0.00%)       62.98  (   0.47%)

thanks,
Chenyu