linux-kernel - Re: [PATCH 1/2] sched/uclamp: Add a new sysctl to control RT default boost value

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Message-ID: <20200518164929.dja4ry6iiq3jny72@e107158-lin.cambridge.arm.com>
Date:   Mon, 18 May 2020 17:49:30 +0100
From:   Qais Yousef <qais.yousef@....com>
To:     Dietmar Eggemann <dietmar.eggemann@....com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Jonathan Corbet <corbet@....net>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Iurii Zaikin <yzaikin@...gle.com>,
        Quentin Perret <qperret@...gle.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Patrick Bellasi <patrick.bellasi@...bug.net>,
        Pavan Kondeti <pkondeti@...eaurora.org>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 1/2] sched/uclamp: Add a new sysctl to control RT default
 boost value

On 05/18/20 10:31, Dietmar Eggemann wrote:
> On 11/05/2020 17:40, Qais Yousef wrote:
> 
> [..]
> 
> > @@ -790,6 +790,26 @@ unsigned int sysctl_sched_uclamp_util_min = SCHED_CAPACITY_SCALE;
> >  /* Max allowed maximum utilization */
> >  unsigned int sysctl_sched_uclamp_util_max = SCHED_CAPACITY_SCALE;
> >  
> > +/*
> > + * By default RT tasks run at the maximum performance point/capacity of the
> > + * system. Uclamp enforces this by always setting UCLAMP_MIN of RT tasks to
> > + * SCHED_CAPACITY_SCALE.
> > + *
> > + * This knob allows admins to change the default behavior when uclamp is being
> > + * used. In battery powered devices, particularly, running at the maximum
> > + * capacity and frequency will increase energy consumption and shorten the
> > + * battery life.
> > + *
> > + * This knob only affects RT tasks that their uclamp_se->user_defined == false.
> 
> Nit pick: Isn't there a verb missing in this sentence?
> 
> [...]
> 
> > @@ -1114,12 +1161,13 @@ int sysctl_sched_uclamp_handler(struct ctl_table *table, int write,
> >  				loff_t *ppos)
> >  {
> >  	bool update_root_tg = false;
> > -	int old_min, old_max;
> > +	int old_min, old_max, old_min_rt;
> 
> Nit pick: Order local variable declarations according to length.
> 
> [...]
> 
> > @@ -1128,7 +1176,9 @@ int sysctl_sched_uclamp_handler(struct ctl_table *table, int write,
> >  		goto done;
> >  
> >  	if (sysctl_sched_uclamp_util_min > sysctl_sched_uclamp_util_max ||
> > -	    sysctl_sched_uclamp_util_max > SCHED_CAPACITY_SCALE) {
> > +	    sysctl_sched_uclamp_util_max > SCHED_CAPACITY_SCALE		||
> 
> Nit pick: This extra space looks weird to me.
> 
> [...]
> 
> Apart from that, LGTM
> 
> For both patches of this v5:
> 
> Reviewed-by: Dietmar Eggemann <dietmar.eggemann@....com>

Thanks Dietmar and Patrick.

Peter, let me know if you'd like me to address the nitpicks or you're okay with
this as-is.

Thanks!

--
Qais Yousef