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Date: Wed, 03 Apr 2013 13:38:20 +0800
From: Michael Wang <wangyun@linux.vnet.ibm.com>
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To: Alex Shi <alex.shi@intel.com>
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Subject: Re: [patch v3 0/8] sched: use runnable avg in load balance
References: <1364873008-3169-1-git-send-email-alex.shi@intel.com> <515A877B.3020908@linux.vnet.ibm.com> <515A9859.6000606@intel.com> <515B97FF.2040409@linux.vnet.ibm.com> <515B9A7A.6030807@intel.com> <515BA0B7.2090906@linux.vnet.ibm.com> <515BAFE6.1020804@intel.com>
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On 04/03/2013 12:28 PM, Alex Shi wrote:
[snip]
> 
> but the patch may cause some unfairness if this/prev cpu are not burst at 
> same time. So could like try the following patch?

I will try it later, some doubt below :)

[snip]
> +
> +	if (cpu_rq(this_cpu)->avg_idle < sysctl_sched_migration_cost ||
> +		cpu_rq(prev_cpu)->avg_idle < sysctl_sched_migration_cost)
> +		burst= 1;
> +
> +	/* use instant load for bursty waking up */
> +	if (!burst) {
> +		load = source_load(prev_cpu, idx);
> +		this_load = target_load(this_cpu, idx);
> +	} else {
> +		load = cpu_rq(prev_cpu)->load.weight;
> +		this_load = cpu_rq(this_cpu)->load.weight;

Ok, my understanding is, we want pull if 'prev_cpu' is burst, and don't
want pull if 'this_cpu' is burst, correct?

And we do this by guess the load higher or lower, is that right?

And I think target_load() is capable enough to choose the higher load,
if 'cpu_rq(cpu)->load.weight' is really higher, the results will be the
same.

So what about this:

	/* prefer higher load if burst */
	load = burst_prev ?
		target_load(prev_cpu, idx) : source_load(prev_cpu, idx);

	this_load = target_load(this_cpu, idx);

Regards,
Michael Wang

> +	}
> 
>  	/*
>  	 * If sync wakeup then subtract the (maximum possible)
>