linux-kernel - Re: [RFC PATCH 0/2] sched: move content out of core files for load average

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Date:	Fri, 19 Apr 2013 23:05:30 +0600
From:	Rakib Mullick <rakib.mullick@...il.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 0/2] sched: move content out of core files for load average

On Fri, Apr 19, 2013 at 2:25 PM, Ingo Molnar <mingo@...nel.org> wrote:
>
> * Paul Gortmaker <paul.gortmaker@...driver.com> wrote:
>
>> On 13-04-18 07:14 AM, Peter Zijlstra wrote:
>> > On Mon, 2013-04-15 at 11:33 +0200, Ingo Molnar wrote:
>> >> * Paul Gortmaker <paul.gortmaker@...driver.com> wrote:
>> >>
>> >>> Recent activity has had a focus on moving functionally related blocks of stuff
>> >>> out of sched/core.c into stand-alone files.  The code relating to load average
>> >>> calculations has grown significantly enough recently to warrant placing it in a
>> >>> separate file.
>> >>>
>> >>> Here we do that, and in doing so, we shed ~20k of code from sched/core.c (~10%).
>> >>>
>> >>> A couple small static functions in the core sched.h header were also localized
>> >>> to their singular user in sched/fair.c at the same time, with the goal to also
>> >>> reduce the amount of "broadcast" content in that sched.h file.
>> >>
>> >> Nice!
>> >>
>> >> Peter, is this (and the naming of the new file) fine with you too?
>> >
>> > Yes and no.. that is I do like the change, but I don't like the
>> > filename. We have _waaaay_ too many different things we call load_avg.
>> >
>> > That said, I'm having a somewhat hard time coming up with a coherent
>> > alternative :/
>>
>> Several of the relocated functions start their name with "calc_load..."
>> Does "calc_load.c" sound any better?
>
> Peter has a point about load_avg being somewhat of a misnomer: that's not your
> fault in any way, we created overlapping naming within the scheduler and are now
> hurting from it.
>
> Here are the main scheduler 'load' concepts we have right now:
>
>  - The externally visible 'average load' value extracted by tools like 'top' via
>    /proc/loadavg and handled by fs/proc/loadavg.c. Internally the naming is all
>    over the map: the fields that are updated are named 'avenrun[]', most other
>    variables and methods are named calc_load_*(), and a few callbacks are named
>    *_cpu_load_*().
>
>  - rq->cpu_load, a weighted, vectored scheduler-internal notion of task load
>    average with multiple run length averages. Only exposed by debug interfaces but
>    otherwise relied on by the scheduler for SMP load balancing.
>
>  - se->avg - per entity (per task) load average. This is integrated differently
>    from the cpu_load - but work is ongoing to possibly integrate it with the
>    rq->cpu_load metric. This metric is used for CPU internal execution time
>    allocation and timeslicing, based on nice value priorities and cgroup
>    weights and constraints.
>
> Work is ongoing to integrate rq->cpu_load and se->avg - eventually they will
> become one metric.
>
> It might eventually make sense to integrate the 'average load' calculation as well
> with all this - as they really have a similar purpose, the avenload[] vector of
> averages is conceptually similar to the rq->cpu_load[] vector of averages.
>
> So I'd suggest to side-step all that existing confusion and simply name the new
> file kernel/sched/proc.c - our external /proc scheduler ABI towards userspace.
> This is similar to the already existing kernel/irq/proc.c pattern.
>
Well, kernel/sched/stat.c - also exposes scheduler ABI to userspace.
Aren't these things going to introduce confusion (stat.c and proc.c
under same sched directory) ?

Thanks,
Rakib
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