linux-kernel - Re: [PATCH 04/10] sched/debug: Increase SCHEDSTAT

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Message-ID: <ZfAoEmH6KRhjyUor@gmail.com>
Date: Tue, 12 Mar 2024 11:01:54 +0100
From: Ingo Molnar <mingo@...nel.org>
To: Shrikanth Hegde <sshegde@...ux.ibm.com>
Cc: linux-kernel@...r.kernel.org,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Valentin Schneider <vschneid@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	"Gautham R . Shenoy" <gautham.shenoy@....com>
Subject: Re: [PATCH 04/10] sched/debug: Increase SCHEDSTAT_VERSION to 16


* Shrikanth Hegde <sshegde@...ux.ibm.com> wrote:

> 
> 
> On 3/8/24 4:28 PM, Ingo Molnar wrote:
> > We changed the order of definitions within 'enum cpu_idle_type',
> > which changed the order of [CPU_MAX_IDLE_TYPES] columns in
> > show_schedstat().
> > 
> 
> > +++ b/kernel/sched/stats.c
> > @@ -113,7 +113,7 @@ void __update_stats_enqueue_sleeper(struct rq *rq, struct task_struct *p,
> >   * Bump this up when changing the output format or the meaning of an existing
> >   * format, so that tools can adapt (or abort)
> >   */
> > -#define SCHEDSTAT_VERSION 15
> > +#define SCHEDSTAT_VERSION 16
> 
> Please add the info about version, and change of the order 
> briefly in Documentation/scheduler/sched-stats.rst as well.

Good point, I've added this paragraph to sched-stats.rst:

 +Version 16 of schedstats changed the order of definitions within
 +'enum cpu_idle_type', which changed the order of [CPU_MAX_IDLE_TYPES]
 +columns in show_schedstat(). In particular the position of CPU_IDLE
 +and __CPU_NOT_IDLE changed places. The size of the array is unchanged.

> One recent user that I recollect is sched scoreboard. Version number should 
> be able to help the users when they it is breaking their scripts. 
> 
> +Gautham, Any thoughts?

If it's really a problem, I suspect we could maintain the v15 order of 
output.

Thanks,

	Ingo