linux-kernel - Re: [PATCH] sched/fair: Fix update_min_vruntime() to get proper min

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Date:   Fri, 9 Sep 2016 11:46:00 +0900
From:   Byungchul Park <byungchul.park@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     mingo@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched/fair: Fix update_min_vruntime() to get proper
 min_vruntime

On Tue, Sep 06, 2016 at 10:48:39AM +0200, Peter Zijlstra wrote:
> On Tue, Sep 06, 2016 at 02:05:17PM +0900, Byungchul Park wrote:
> > From 295895be8befbab040d6054bb8186c03daabcedd Mon Sep 17 00:00:00 2001
> > From: Byungchul Park <byungchul.park@....com>
> > Date: Tue, 6 Sep 2016 12:22:26 +0900
> > Subject: [PATCH] sched/fair: Fix update_min_vruntime() to get proper
> >  min_vruntime
> > 
> > Commit 97a7142 'sched/fair: Make update_min_vruntime() more readable'
> > introduces a bug that cfs_rq gets a wrong min_vruntime if
> > !cfs_rq->rb_leftmost && cfs_rq->curr. This fixes it and makes it more
> > readable and simple.
> 
> Urgh, I actually stared at that patch for quite a time and somehow
> convinced myself it was good. I actually considered that scenario I
> think.
> 
> /me thinks more..
> 
> Argh, I'm an idiot, you're right. By using min_vruntime() on
> cfs_rq->curr we take the leftmost and fail to advance min_vruntime in
> that case.
> 
> I'll ask Ingo to take the patch out.

Ok. But I think the combined one is more readable.
Don't you think so. It's ok even if you don't.

Thank you,
Byungchul