linux-kernel - Re: [RFC PATCH 10/16 v3] Workload Consolidation APIs

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Date:	Tue, 3 Jun 2014 14:22:35 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Yuyang Du <yuyang.du@...el.com>
Cc:	mingo@...hat.com, rafael.j.wysocki@...el.com,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	arjan.van.de.ven@...el.com, len.brown@...el.com,
	alan.cox@...el.com, mark.gross@...el.com, pjt@...gle.com,
	bsegall@...gle.com, morten.rasmussen@....com,
	vincent.guittot@...aro.org, rajeev.d.muralidhar@...el.com,
	vishwesh.m.rudramuni@...el.com, nicole.chalhoub@...el.com,
	ajaya.durg@...el.com, harinarayanan.seshadri@...el.com,
	jacob.jun.pan@...ux.intel.com, fengguang.wu@...el.com
Subject: Re: [RFC PATCH 10/16 v3] Workload Consolidation APIs

On Fri, May 30, 2014 at 02:36:06PM +0800, Yuyang Du wrote:
> Currently, CPU CC is per CPU. To consolidate, the formula is based on a heuristic.
> Suppose we have 2 CPUs, their task concurrency over time is ('-' means no
> task, 'x' having tasks):
> 
> 1)
> CPU0: ---xxxx---------- (CC[0])
> CPU1: ---------xxxx---- (CC[1])
> 
> 2)
> CPU0: ---xxxx---------- (CC[0])
> CPU1: ---xxxx---------- (CC[1])
> 
> If we consolidate CPU0 and CPU1, the consolidated CC will be: CC' = CC[0] +
> CC[1] for case 1 and CC'' = (CC[0] + CC[1]) * 2 for case 2. For the cases in
> between case 1 and 2 in terms of how xxx overlaps, the CC should be between
> CC' and CC''. So, we uniformly use this condition for consolidation (suppose
> we consolidate m CPUs to n CPUs, m > n):
> 
> (CC[0] + CC[1] + ... + CC[m-2] + CC[m-1]) * (n + log(m-n)) >=<? (1 * n) * n *
> consolidating_coefficient
> 
> The consolidating_coefficient could be like 100% or more or less.
> 

I'm still struggling to match that to the code presented.

> +/*
> + * as of now, we have the following assumption
> + * 1) every sched_group has the same weight
> + * 2) every CPU has the same computing power
> + */

Those are complete non starters.

> +/*
> + * wc_nonshielded_mask - return the nonshielded cpus in the @mask,
> + * which is unmasked by the shielded cpus
> + *
> + * traverse downward the sched_domain tree when the sched_domain contains
> + * flag SD_WORKLOAD_CONSOLIDATION, each sd may have more than two groups

WTF is a shielded/nonshielded cpu?

> +static int cpu_task_hot(struct task_struct *p, u64 now)
> +{
> +	s64 delta;
> +
> +	if (p->sched_class != &fair_sched_class)
> +		return 0;
> +
> +	if (unlikely(p->policy == SCHED_IDLE))
> +		return 0;
> +
> +	if (wc_push_hot_task)
> +		return 0;
> +
> +	/*
> +	 * Buddy candidates are cache hot:
> +	 */
> +	if (sched_feat(CACHE_HOT_BUDDY) && this_rq()->nr_running &&
> +			(&p->se == cfs_rq_of(&p->se)->next ||
> +			 &p->se == cfs_rq_of(&p->se)->last))
> +		return 1;
> +
> +	if (sysctl_sched_migration_cost == -1)
> +		return 1;
> +	if (sysctl_sched_migration_cost == 0)
> +		return 0;
> +
> +	delta = now - p->se.exec_start;
> +
> +	return delta < (s64)sysctl_sched_migration_cost;
> +}

In what universe to we need an exact copy of task_hot() ?

and on and on it goes.. :-(

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