Re: [PATCH-cpuset v10 2/2] cpuset: use Union-Find to optimize the merging of cpumasks

[Waiman Long]

On 7/3/24 06:49, Xavier wrote:
> Hi Michal and Longman,
>
> Please confirm my explanation about cgroup v2 below.
>
>
> At 2024-07-03 17:40:49, "Michal Koutný" <mkoutny@xxxxxxxx> wrote:
> > On Wed, Jul 03, 2024 at 02:37:27PM GMT, Xavier <xavier_qy@xxxxxxx> wrote:
> > > @@ -1102,31 +1101,25 @@ static int generate_sched_domains(cpumask_var_t **domains,
> > >   	if (root_load_balance && (csn == 1))
> > >   		goto single_root_domain;
> > >   
> > > -	for (i = 0; i < csn; i++)
> > > -		csa[i]->pn = i;
> > > -	ndoms = csn;
> > > -
> > > -restart:
> > > -	/* Find the best partition (set of sched domains) */
> > > -	for (i = 0; i < csn; i++) {
> > > -		struct cpuset *a = csa[i];
> > > -		int apn = a->pn;
> > > -
> > > -		for (j = 0; j < csn; j++) {
> > > -			struct cpuset *b = csa[j];
> > > -			int bpn = b->pn;
> > > -
> > > -			if (apn != bpn && cpusets_overlap(a, b)) {
> > > -				for (k = 0; k < csn; k++) {
> > > -					struct cpuset *c = csa[k];
> > > +	if (!cgrpv2) {
> > I'm surprised that original code wasn't branched on this on you add it
> > here. Why is UF used only for v1 code?
> In the Patch v6, I explained to Longman that based on his new patch, the overlapping check and
> merge operations for cpusets are skipped in the case of cgroup v2. Because for cgroup v2,
> doms[i] is merely copied from csa[i] rather than merged.
> This needs further confirmation from Longman.

Actually, I would like to keep the cpuset merging part for both cgroup 
v1 and v2. I did notice that the hotplug code path can sometimes cause 
overlapping partition roots in some intermediate states. I will try to 
get it of that and use the merging part to verify that all partition 
roots are mutually exclusive.

Cheers,
Longman