linux-kernel - Re: [RFC PATCH] PM/CPU: Parallel enabling nonboot cpus with resume devices

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Message-ID: <20140723092154.GH20603@laptop.programming.kicks-ass.net>
Date:	Wed, 23 Jul 2014 11:21:54 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Lan Tianyu <tianyu.lan@...el.com>
Cc:	rjw@...ysocki.net, len.brown@...el.com, pavel@....cz,
	toshi.kani@...com, mingo@...nel.org, akpm@...ux-foundation.org,
	todd.e.brandt@...ux.intel.com, fabf@...net.be,
	srivatsa.bhat@...ux.vnet.ibm.com, ego@...ux.vnet.ibm.com,
	rafael.j.wysocki@...el.com, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC PATCH] PM/CPU: Parallel enabling nonboot cpus with resume
 devices

On Wed, Jul 23, 2014 at 05:11:34PM +0800, Lan Tianyu wrote:
> In the current world, all nonboot cpus are enabled serially during system
> resume. System resume sequence is that boot cpu enables nonboot cpu one by
> one and then resume devices. Before resuming devices, there are few tasks
> assigned to nonboot cpus after they are brought up. This waste cpu usage.
> 
> To accelerate S3, this patches adds a new kernel configure
> PM_PARALLEL_CPU_UP_FOR_SUSPEND to allow boot cpu to go forward to resume
> devices after bringing up one nonboot cpu. The nonboot cpu will be in charge
> of bringing up other cpus. This makes enabling cpu2~x parallel with resuming
> devices. From the test result on 4 logical core laptop, the time of resume
> device almost wasn't affected by enabling nonboot cpus lately while the start
> point is almost 30ms earlier than before.

Why is this a CONFIG and why do we want to add more warts to the cpu
hotplug instead of fixing it 'proper'?
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