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

[Peter Zijlstra]

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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