linux-kernel - Re: [RFC][PATCH v5 05/14] sched: add a packing level knob

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Message-ID: <20131112105508.GN5056@laptop.programming.kicks-ass.net>
Date:	Tue, 12 Nov 2013 11:55:08 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vincent Guittot <vincent.guittot@...aro.org>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>, Paul Turner <pjt@...gle.com>,
	Morten Rasmussen <Morten.Rasmussen@....com>,
	"cmetcalf@...era.com" <cmetcalf@...era.com>,
	"tony.luck@...el.com" <tony.luck@...el.com>,
	Alex Shi <alex.shi@...el.com>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Jonathan Corbet <corbet@....net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Len Brown <len.brown@...el.com>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Amit Kucheria <amit.kucheria@...aro.org>,
	Lukasz Majewski <l.majewski@...sung.com>
Subject: Re: [RFC][PATCH v5 05/14] sched: add a packing level knob

On Tue, Nov 12, 2013 at 11:44:15AM +0100, Vincent Guittot wrote:
> On 12 November 2013 11:32, Peter Zijlstra <peterz@...radead.org> wrote:
> > On Fri, Oct 18, 2013 at 01:52:18PM +0200, Vincent Guittot wrote:
> >> +int sched_proc_update_packing(struct ctl_table *table, int write,
> >> +             void __user *buffer, size_t *lenp,
> >> +             loff_t *ppos)
> >> +{
> >> +     int ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
> >> +     if (ret || !write)
> >> +             return ret;
> >> +
> >> +     if (sysctl_sched_packing_level)
> >> +             sd_pack_threshold = (100 * 1024) / sysctl_sched_packing_level;
> >> +
> >> +     return 0;
> >> +}
> >
> >> +#ifdef CONFIG_SCHED_PACKING_TASKS
> >> +static int min_sched_packing_level;
> >> +static int max_sched_packing_level = 100;
> >> +#endif /* CONFIG_SMP */
> >
> >> +#ifdef CONFIG_SCHED_PACKING_TASKS
> >> +     {
> >> +             .procname       = "sched_packing_level",
> >> +             .data           = &sysctl_sched_packing_level,
> >> +             .maxlen         = sizeof(int),
> >> +             .mode           = 0644,
> >> +             .proc_handler   = sched_proc_update_packing,
> >> +             .extra1         = &min_sched_packing_level,
> >> +             .extra2         = &max_sched_packing_level,
> >> +     },
> >> +#endif
> >
> > Shouldn't min_sched_packing_level be 1? Userspace can now write 0 and
> > expect something; but then we don't update sd_pack_threshold so nothing
> > really changed.
> 
> value 0 is used to disable to packing feature and the scheduler falls
> back to default behavior. This value is tested when setting which cpus
> will be used by the scheduler.

I suspected as much, but it wasn't clear from the Changelog, the patch
or any comments. Plz as to fix.
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