linux-kernel - Re: [RFC PATCH V3 0/3] PM/CPU: Parallel enalbing nonboot cpus with resume devices

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Message-ID: <20141008205441.GJ4750@worktop.programming.kicks-ass.net>
Date:	Wed, 8 Oct 2014 22:54:41 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Lan Tianyu <tianyu.lan@...el.com>
Cc:	mingo@...nel.org, rafael.j.wysocki@...el.com, toshi.kani@...com,
	akpm@...ux-foundation.org, ktkhai@...allels.com, fabf@...net.be,
	laijs@...fujitsu.com, srivatsa.bhat@...ux.vnet.ibm.com,
	ego@...ux.vnet.ibm.com, srivatsa@....edu, viresh.kumar@...aro.org,
	todd.e.brandt@...ux.intel.com, tipbot@...or.com,
	wangyun@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC PATCH V3 0/3] PM/CPU: Parallel enalbing nonboot cpus with
 resume devices

On Thu, Sep 25, 2014 at 04:32:02PM +0800, Lan Tianyu wrote:
> This patchset is to parallel enabling nonboot cpus with resuming devices
> during system resume in order to accelerate S2RAM. From test result on
> a 8 logical core Haswell machine, system resume time reduces from 347ms
> to 217ms with this patchset.
> 
> 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 wastes cpu usage.
> 
> This patchset is to allow boot cpu to go forward to resume devices after
> bringing up one nonboot cpu and starting a thread. The thread will be in
> charge of bringing up other frozen cpus. The thread will be scheduled to
> the first online cpu to run . This makes enabling cpu2~x parallel with
> resuming devices.

So I feel we should really clean up hotplug before doing anything like
this. Its a trainwreck and just piling more and more hacks ontop isn't
going to help any.
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