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Date:   Wed, 12 Jul 2023 11:33:11 -0700
From:   Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
To:     Miaohe Lin <linmiaohe@huawei.com>
Cc:     Peter Zijlstra <peterz@infradead.org>, mingo@redhat.com,
        juri.lelli@redhat.com, vincent.guittot@linaro.org,
        dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com,
        mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com,
        linux-kernel@vger.kernel.org, yu.c.chen@intel.com,
        tim.c.chen@intel.com
Subject: Re: [PATCH] sched/topology: remove unneeded do while loop in
 cpu_attach_domain()
Message-ID: <20230712183310.GA27117@ranerica-svr.sc.intel.com>
References: <20230617081926.2035113-1-linmiaohe@huawei.com>
 <20230620141120.GA2016469@hirez.programming.kicks-ass.net>
 <53a9ec35-8332-755c-40ed-54315ffb0d78@huawei.com>
 <20230621131159.GA23663@ranerica-svr.sc.intel.com>
 <20230621185749.GA24063@ranerica-svr.sc.intel.com>
 <268d9d61-ce17-cda6-7a21-148b518ac323@huawei.com>
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On Sun, Jun 25, 2023 at 09:59:36AM +0800, Miaohe Lin wrote:
> On 2023/6/22 2:57, Ricardo Neri wrote:
> > On Wed, Jun 21, 2023 at 06:11:59AM -0700, Ricardo Neri wrote:
> >> On Wed, Jun 21, 2023 at 10:53:57AM +0800, Miaohe Lin wrote:
> >>> On 2023/6/20 22:11, Peter Zijlstra wrote:
> >>>> On Sat, Jun 17, 2023 at 04:19:26PM +0800, Miaohe Lin wrote:
> >>>>> When sg != sd->groups, the do while loop would cause deadloop here. But
> >>>>> that won't occur because sg is always equal to sd->groups now. Remove
> >>>>> this unneeded do while loop.
> >>>>
> >>>> This Changelog makes no sense to me.. Yes, as is the do {} while loop is
> >>>> dead code, but it *should* have read like:
> >>>>
> >>>> 	do {
> >>>> 		sg->flags = 0;
> >>>> 		sg = sg->next;
> >>>> 	} while (sg != sd->groups);
> >>
> >> Yes, I agree that this is the correct solution.
> > 
> > I take this back. I think we should do this:
> > 
> > @@ -758,19 +758,14 @@ cpu_attach_domain(struct sched_domain *sd, struct root_domain *rd, int cpu)
> >  		sd = sd->parent;
> >  		destroy_sched_domain(tmp);
> >  		if (sd) {
> > -			struct sched_group *sg = sd->groups;
> > -
> >  			/*
> >  			 * sched groups hold the flags of the child sched
> >  			 * domain for convenience. Clear such flags since
> >  			 * the child is being destroyed.
> >  			 */
> > -			do {
> > -				sg->flags = 0;
> > -			} while (sg != sd->groups);
> > +			sd->groups->flags = 0;
> >  
> >  			sd->child = NULL;
> > -		}
> >  	}
> >  
> >  	sched_domain_debug(sd, cpu);
> > 
> > A comment from Chenyu made got me thinking that we should only clear the
> > flags of the local group as viewed from the parent domain. This is because
> > the domain being degenerated defines the flags of such group only.
> 
> This looks better to my patch. Thanks.

Are you planning on posting a v2? Maybe I missed it.
>