linux-kernel - Re: [tip: sched/core] sched: Make struct sched_statistics independent of fair sched class

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Message-ID: <20210921074042.GU2116@kadam>
Date:   Tue, 21 Sep 2021 10:40:42 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, linux-tip-commits@...r.kernel.org,
        Yafang Shao <laoar.shao@...il.com>,
        Mel Gorman <mgorman@...e.de>, x86@...nel.org
Subject: Re: [tip: sched/core] sched: Make struct sched_statistics
 independent of fair sched class

On Tue, Sep 21, 2021 at 09:17:07AM +0200, Peter Zijlstra wrote:
> On Tue, Sep 21, 2021 at 09:17:27AM +0300, Dan Carpenter wrote:
> > On Thu, Sep 16, 2021 at 11:59:30AM -0000, tip-bot2 for Yafang Shao wrote:
> > > @@ -11424,7 +11441,7 @@ int alloc_fair_sched_group(struct task_group *tg, struct task_group *parent)
> > >  		if (!cfs_rq)
> > >  			goto err;
> > >  
> > > -		se = kzalloc_node(sizeof(struct sched_entity),
> > > +		se = kzalloc_node(sizeof(struct sched_entity_stats),
> > 
> > This wasn't there in the original patch and it causes a Smatch warning
> 
> What original patch? It's part of the v4 posting.
> 
> > because "se" is declared as a "sched_entity" but it's allocating a
> > larger "sched_entity_stats" which contains a sched_entity.
> 
> Yep, on purpose.
> 
> > To me, ideally, we would update the type of se.
> 
> That's a lot of churn for very little gain. I can rewrite it like:
> 
> 	struct sched_entity_stats *ses = kzalloc_node(sizeof(*ses),...);
> 	se = &ses->se;
> 
> If that makes smatch happy. It's the exact same thing tho because we
> force ses->se to be at 0 offset.

I mean, I understood what the allocation was doing and that this was a
way to avoid churn.  But it's pretty confusing, because every "se" is
really an "ses" now right?

Anyway, just leave it.  It's fine.

regards,
dan carpenter