linux-kernel - Re: [PATCH 0/2] Run callback of device

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Date:	Sat, 08 Jun 2013 09:17:13 +0800
From:	Yanmin Zhang <yanmin_zhang@...ux.intel.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	shuox.liu@...el.com, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org, pavel@....cz, len.brown@...el.com,
	gregkh@...uxfoundation.org
Subject: Re: [PATCH 0/2] Run callback of device_prepare/complete consistently

On Sat, 2013-06-08 at 02:54 +0200, Rafael J. Wysocki wrote:
> On Saturday, June 08, 2013 08:42:12 AM Yanmin Zhang wrote:
> > On Fri, 2013-06-07 at 12:36 +0200, Rafael J. Wysocki wrote:
> > > On Friday, June 07, 2013 04:20:30 PM shuox.liu@...el.com wrote:
> > > > dpm_run_callback is used in other stages of power states changing.
> > > > It provides debug info message and time measurement when call these
> > > > callback. We also want to benefit ->prepare and ->complete.
> > > > 
> > > > [PATCH 1/2] PM: use dpm_run_callback in device_prepare
> > > > [PATCH 2/2] PM: add dpm_run_callback_void and use it in device_complete
> > > 
> > > Is this an "Oh, why don't we do that?" series, or is it useful for anything
> > > in practice?  I'm asking, because we haven't added that stuff to start with
> > > since we didn't see why it would be useful to anyone.
> > > 
> > > And while patch [1/2] reduces the code size (by 1 line), so I can see some
> > > (tiny) benefit from applying it, patch [2/2] adds more code and is there any
> > > paractical reason?
> > Sometimes, suspend-to-ram path spends too much time (either suspend slowly
> > or wakeup slowly) and we need optimize it.
> > With the 2 patches, we could collect initcall_debug printk info and manually
> > check what prepare/complete callbacks consume too much time.
> 
> Well, can you point me to a single driver where prepare/complete causes this
> type of problems to happen?

That's a good question. We are enabling Android mobiles and need optimize
suspend-to-ram. In the current upstream, we don't find a driver's prepare/complete
callback spends too much time.


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