linux-kernel - Re: [PATCH] sched/topology: remove unneeded do while loop in cpu_attach

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Date:   Wed, 21 Jun 2023 10:53:57 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     <mingo@...hat.com>, <juri.lelli@...hat.com>,
        <vincent.guittot@...aro.org>, <dietmar.eggemann@....com>,
        <rostedt@...dmis.org>, <bsegall@...gle.com>, <mgorman@...e.de>,
        <bristot@...hat.com>, <vschneid@...hat.com>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sched/topology: remove unneeded do while loop in
 cpu_attach_domain()

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);
> 
> as I noted here:
> 
>   https://lore.kernel.org/all/20230523105935.GN83892@hirez.programming.kicks-ass.net/T/#u

[1]

> 
> So what this changelog should argue is how there cannot be multiple
> groups here -- or if there can be, add the missing iteration.

[1] said:
"
Yes, I missed that.

That being said, the only reason for sd to be degenerate is that there
is only 1 group. Otherwise we will keep it and degenerate parents
instead
"

IOW, "sg = sg->next;" is missed intentionally in the do while{} loop to show that
there's only 1 sched group. This looks weird to me but no persist on change the code.

Thanks.