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From: Qais Yousef <qais.yousef@arm.com>
To: Quentin Perret <qperret@google.com>
Cc: Ingo Molnar <mingo@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Jonathan Corbet <corbet@lwn.net>,
	Juri Lelli <juri.lelli@redhat.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
	Luis Chamberlain <mcgrof@kernel.org>,
	Kees Cook <keescook@chromium.org>,
	Iurii Zaikin <yzaikin@google.com>,
	Valentin Schneider <valentin.schneider@arm.com>,
	Patrick Bellasi <patrick.bellasi@matbug.net>,
	Pavan Kondeti <pkondeti@codeaurora.org>,
	linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 1/2] sched/uclamp: Add a new sysctl to control RT default boost value
Date: Mon, 20 Apr 2020 16:08:40 +0100
Message-ID: <20200420150839.ysh3ijfjftyzg7jw@e107158-lin.cambridge.arm.com> (raw)
In-Reply-To: <20200415101122.GA14447@google.com>

Hi Quentin

On 04/15/20 11:11, Quentin Perret wrote:
> Hi Qais,
> 
> On Friday 03 Apr 2020 at 13:30:19 (+0100), Qais Yousef wrote:
> <snip>
> > +	/*
> > +	 * The new value will be applied to all RT tasks the next time they
> > +	 * wakeup, assuming the task is using the system default and not a user
> > +	 * specified value. In the latter we shall leave the value as the user
> > +	 * requested.
> > +	 */
> >  	if (sysctl_sched_uclamp_util_min > sysctl_sched_uclamp_util_max ||
> >  	    sysctl_sched_uclamp_util_max > SCHED_CAPACITY_SCALE) {
> >  		result = -EINVAL;
> >  		goto undo;
> >  	}
> >  
> > +	if (sysctl_sched_rt_default_uclamp_util_min > SCHED_CAPACITY_SCALE) {
> > +		result = -EINVAL;
> > +		goto undo;
> > +	}
> 
> Hmm, checking:
> 
> 	if (sysctl_sched_rt_default_uclamp_util_min > sysctl_sched_uclamp_util_min)
> 
> would probably make sense too, but then that would make writing in
> sysctl_sched_uclamp_util_min cumbersome for sysadmins as they'd need to
> lower the rt default first. Is that the reason for checking against
> SCHED_CAPACITY_SCALE? That might deserve a comment or something.

There's no need for that extra diff. That constraint will be applied
automatically when calculating the effective value.

The check for SCHED_CAPACITY_SCALE is a a range check. The possible value is
[0:SCHED_CAPACITY_SCALE].

Does this answer your question? I could add a comment that all the uclamp
sysctls need to be within this range.

> 
> <snip>
> > @@ -1241,9 +1293,13 @@ static void uclamp_fork(struct task_struct *p)
> >  	for_each_clamp_id(clamp_id) {
> >  		unsigned int clamp_value = uclamp_none(clamp_id);
> >  
> > -		/* By default, RT tasks always get 100% boost */
> > +		/*
> > +		 * By default, RT tasks always get 100% boost, which the admins
> > +		 * are allowed to change via
> > +		 * sysctl_sched_rt_default_uclamp_util_min knob.
> > +		 */
> >  		if (unlikely(rt_task(p) && clamp_id == UCLAMP_MIN))
> > -			clamp_value = uclamp_none(UCLAMP_MAX);
> > +			clamp_value = sysctl_sched_rt_default_uclamp_util_min;
> >  
> >  		uclamp_se_set(&p->uclamp_req[clamp_id], clamp_value, false);
> >  	}
> 
> And that, as per 20200414161320.251897-1-qperret@google.com, should not
> be there :)

Yep saw it. Thanks for fixing it!

> 
> Otherwise the patch pretty looks good to me!

Cheers

--
Qais Yousef

  reply index

Thread overview: 68+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-03 12:30 Qais Yousef
2020-04-03 12:30 ` [PATCH 2/2] Documentation/sysctl: Document uclamp sysctl knobs Qais Yousef
2020-04-14 18:21 ` [PATCH 1/2] sched/uclamp: Add a new sysctl to control RT default boost value Patrick Bellasi
2020-04-15  7:46   ` Patrick Bellasi
2020-04-20 15:04     ` Qais Yousef
2020-04-20  8:24   ` Dietmar Eggemann
2020-04-20 15:19     ` Qais Yousef
2020-04-21  0:52       ` Steven Rostedt
2020-04-21 11:16         ` Dietmar Eggemann
2020-04-21 11:23           ` Qais Yousef
2020-04-20 14:50   ` Qais Yousef
2020-04-15 10:11 ` Quentin Perret
2020-04-20 15:08   ` Qais Yousef [this message]
2020-04-20  8:29 ` Dietmar Eggemann
2020-04-20 15:13   ` Qais Yousef
2020-04-21 11:18     ` Dietmar Eggemann
2020-04-21 11:27       ` Qais Yousef
2020-04-22 10:59         ` Dietmar Eggemann
2020-04-22 13:13           ` Qais Yousef
2020-05-11 15:40 Qais Yousef
2020-05-11 17:18 ` Qais Yousef
2020-05-12  2:10 ` Pavan Kondeti
2020-05-12 11:46   ` Qais Yousef
2020-05-15 11:08 ` Patrick Bellasi
2020-05-18  8:31 ` Dietmar Eggemann
2020-05-18 16:49   ` Qais Yousef
2020-05-28 13:23 ` Peter Zijlstra
2020-05-28 15:58   ` Qais Yousef
2020-05-28 16:11     ` Peter Zijlstra
2020-05-28 16:51       ` Qais Yousef
2020-05-28 18:29         ` Peter Zijlstra
2020-05-28 19:08           ` Patrick Bellasi
2020-05-28 19:20           ` Dietmar Eggemann
2020-05-29  9:11           ` Qais Yousef
2020-05-29 10:21         ` Mel Gorman
2020-05-29 15:11           ` Qais Yousef
2020-05-29 16:02             ` Mel Gorman
2020-05-29 16:05               ` Qais Yousef
2020-05-29 10:08       ` Mel Gorman
2020-05-29 16:04         ` Qais Yousef
2020-05-29 16:57           ` Mel Gorman
2020-06-02 16:46         ` Dietmar Eggemann
2020-06-03  8:29           ` Patrick Bellasi
2020-06-03 10:10             ` Mel Gorman
2020-06-03 14:59               ` Vincent Guittot
2020-06-03 16:52                 ` Qais Yousef
2020-06-04 12:14                   ` Vincent Guittot
2020-06-05 10:45                     ` Qais Yousef
2020-06-09 15:29                       ` Vincent Guittot
2020-06-08 12:31                     ` Qais Yousef
2020-06-08 13:06                       ` Valentin Schneider
2020-06-08 14:44                       ` Steven Rostedt
2020-06-11 10:13                         ` Qais Yousef
2020-06-09 17:10                       ` Vincent Guittot
2020-06-11 10:24                         ` Qais Yousef
2020-06-11 12:01                           ` Vincent Guittot
2020-06-23 15:44                             ` Qais Yousef
2020-06-24  8:45                               ` Vincent Guittot
2020-06-05  7:55                   ` Patrick Bellasi
2020-06-05 11:32                     ` Qais Yousef
2020-06-05 13:27                       ` Patrick Bellasi
2020-06-03  9:40           ` Mel Gorman
2020-06-03 12:41             ` Qais Yousef
2020-06-04 13:40               ` Mel Gorman
2020-06-05 10:58                 ` Qais Yousef
2020-06-11 10:58                 ` Qais Yousef
2020-06-16 11:08                   ` Qais Yousef
2020-06-16 13:56                     ` Lukasz Luba

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