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Date: Tue, 12 Nov 2013 11:44:15 +0100
Message-ID: <CAKfTPtBymfyQC7=oTscrZVByHmFcgcZM5fPJRssqP9YEQjDECA@mail.gmail.com>
Subject: Re: [RFC][PATCH v5 05/14] sched: add a packing level knob
From: Vincent Guittot <vincent.guittot@linaro.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@kernel.org>, Paul Turner <pjt@google.com>,
        Morten Rasmussen <Morten.Rasmussen@arm.com>,
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        "tony.luck@intel.com" <tony.luck@intel.com>,
        Alex Shi <alex.shi@intel.com>,
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        Len Brown <len.brown@intel.com>,
        Arjan van de Ven <arjan@linux.intel.com>,
        Amit Kucheria <amit.kucheria@linaro.org>,
        Lukasz Majewski <l.majewski@samsung.com>
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On 12 November 2013 11:32, Peter Zijlstra <peterz@infradead.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.