linux-kernel - Re: [PATCH V2 2/2] cpuidle/drivers/menu: Remove get

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Message-ID: <20181012082826.GP9848@hirez.programming.kicks-ass.net>
Date:   Fri, 12 Oct 2018 10:28:26 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     rafael@...nel.org, rjw@...ysocki.net, linux-pm@...r.kernel.org,
        Todd Kjos <tkjos@...gle.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Colin Cross <ccross@...roid.com>,
        Ramesh Thomas <ramesh.thomas@...el.com>,
        Mel Gorman <mgorman@...e.de>, Ingo Molnar <mingo@...hat.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Alex Shi <alex.shi@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2 2/2] cpuidle/drivers/menu: Remove get_loadavg in the
 performance multiplier

On Thu, Oct 04, 2018 at 02:04:03PM +0200, Daniel Lezcano wrote:
> The function get_loadavg() returns almost always zero. To be more
> precise, statistically speaking for a total of 1023379 times passing
> in the function, the load is equal to zero 1020728 times, greater than
> 100, 610 times, the remaining is between 0 and 5.
> 
> In 2011, the get_loadavg() was removed from the Android tree because
> of the above [1]. At this time, the load was:
> 
> unsigned long this_cpu_load(void)
> {
>         struct rq *this = this_rq();
>         return this->cpu_load[0];
> }
> 
> In 2014, the code was changed by commit 372ba8cb46b2 (cpuidle: menu: Lookup CPU
> runqueues less) and the load is:
> 
> void get_iowait_load(unsigned long *nr_waiters, unsigned long *load)
> {
>         struct rq *rq = this_rq();
>         *nr_waiters = atomic_read(&rq->nr_iowait);
>         *load = rq->load.weight;
> }
> 
> with the same result.
> 
> Both measurements show using the load in this code path does no matter
> anymore. Removing it.
> 
> [1] https://android.googlesource.com/kernel/common/+/4dedd9f124703207895777ac6e91dacde0f7cc17
> 
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Todd Kjos <tkjos@...gle.com>
> Cc: Joel Fernandes <joelaf@...gle.com>
> Cc: Colin Cross <ccross@...roid.com>
> Cc: Ramesh Thomas <ramesh.thomas@...el.com>
> Cc: Mel Gorman <mgorman@...e.de>
> Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>

Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>