linux-kernel - Re: [RFC PATCH 01/14] sched: track the runnable average on a per-task entitiy basis

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Message-ID: <1329398878.2293.215.camel@twins>
Date:	Thu, 16 Feb 2012 14:27:58 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Paul Turner <pjt@...gle.com>
Cc:	linux-kernel@...r.kernel.org, Venki Pallipadi <venki@...gle.com>,
	Srivatsa Vaddagiri <vatsa@...ibm.com>,
	Mike Galbraith <efault@....de>,
	Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
	Ben Segall <bsegall@...gle.com>, Ingo Molnar <mingo@...e.hu>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
Subject: Re: [RFC PATCH 01/14] sched: track the runnable average on a
 per-task entitiy basis

On Wed, 2012-02-01 at 17:38 -0800, Paul Turner wrote:
> +static __always_inline u64 decay_load(u64 val, int n)
> +{
> +       for (;n && val;n--) {
> +               val *= 4008;
> +               val >>= 12;
> +       }
> +
> +       return val;
> +}

> +                       sa->runnable_avg_sum =
> +                               decay_load(sa->runnable_avg_sum, 1);
> +                       sa->runnable_avg_period =
> +                               decay_load(sa->runnable_avg_period, 1); 

Since all you ever seem to do is:

  x = decay(x, n);

and frequently run over the line limits it might make sense to either
introduce a CPP helper or make the first argument a pointer and ditch
the return value so we end up with something like:

  decay(&x, n);


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