linux-kernel - Re: [RFC PATCH 14/14] sched: implement usage tracking

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Date:	Thu, 16 Feb 2012 17:58:30 +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 14/14] sched: implement usage tracking

On Wed, 2012-02-01 at 17:38 -0800, Paul Turner wrote:
>  struct sched_avg {
>         u64 runnable_avg_sum, runnable_avg_period;
>         u64 last_runnable_update, decay_count;
> +       u32 usage_avg_sum;

4 byte hole

>         unsigned long load_avg_contrib;
>  
>         int contributes_blocked_load; 
>};


A) Running/Runnable
    - uses last_runnable_update to track
        runnable_avg_sum, usage_avg_sum and runnable_avg_period

B) Blocked
    - uses decay_count to keep track of sleeptime

C) 'Migrate'
    - uses contributes_blocked_load to check if we actually did migrate?

So there's a number of things I don't get, why have
remove_task_load_avg_async() in set_task_rq()? enqueue_entity_load_avg()
can do the __synchronize_entity_decay() thing (and actually does) just
fine, right?

Similarly, why not use last_runnable_update (as last_update) to track
both A and B since a task cannot be in both states at the same time
anyway. If you always update the timestamp you can use it to either
track runnable/usage or decay for sleep.

That would get rid of decay_count and contributes_blocked_load, no?
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