linux-kernel - Re: [RFC][PATCH 0/7] PM: Asynchronous suspend and resume (updated)

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Message-Id: <200908192302.31453.rjw@sisk.pl>
Date:	Wed, 19 Aug 2009 23:02:31 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Zhang Rui <rui.zhang@...el.com>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	"linux-pm" <linux-pm@...ts.linux-foundation.org>,
	"linux-acpi" <linux-acpi@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Len Brown <lenb@...nel.org>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Greg KH <gregkh@...e.de>
Subject: Re: [RFC][PATCH 0/7] PM: Asynchronous suspend and resume (updated)

On Wednesday 19 August 2009, Zhang Rui wrote:
> On Wed, 2009-08-19 at 07:58 +0800, Rafael J. Wysocki wrote:
> > On Tuesday 18 August 2009, Rafael J. Wysocki wrote:
> > > On Tuesday 18 August 2009, Zhang Rui wrote:
> > > > On Mon, 2009-08-17 at 08:15 +0800, Rafael J. Wysocki wrote:
> > > > > On Wednesday 12 August 2009, Rafael J. Wysocki wrote:
> > > > > > Hi,
> > > > > > 
> > > > > > The following patches introduce a mechanism allowing us to execute device
> > > > > > drivers' suspend and resume callbacks asynchronously during system sleep
> > > > > > transitions, such as suspend to RAM.  The idea is explained in the [1/1] patch
> > > > > > message.
> > > > > 
> > > > > Changes:
> > > > > 
> > > > > * Added [1/7] that fixes kerneldoc comments in drivers/base/power/main.c
> > > > >   (this is a 2.6.32 candidate).
> > > > > 
> > > > > * Added [2/7] adding a framework for representing PM link (idea described
> > > > >   in the patch message).
> > > > > 
> > > > > * [3/7] is the async resume patch (idea described in the patch message).
> > > > > 
> > > > > * [4/7] is the async suspend patch.
> > > > > 
> > > > > * [5/7] - [7/7] set async_suspend for devices in a few selected subsystems.
> > > > > 
> > > > > The patches have been tested on HP nx6325.
> > > > > 
> > > > I tried this patch set and it does work. :)
> > > > But unfortunately it doesn't save too much time.
> > > > 
> > > > I still think that the child device should inherit its parent's
> > > > async_suspend flag to do the asynchronous resume more efficiently.
> > > > 
> > > > or at least we should provide such an interface
> > > > in drivers/base/power/common.c, so that device can tell the device core
> > > > to inherit this flag if there is no off-tree dependency.
> > > 
> > > Well, I'd prefer to identify all of the off-tree dependencies that have to be
> > > taken into account and handle all devices asynchronously.
> > 
> > Anyway, I have tested the appended patch on top of [1/7]-[7/7] and my test box
> > appears to work fine with it, although it doesn't work in the "async for all"
> > case.
> > 
> > I guess the next step will be to see which devices are not handled
> > asynchronously with the patch below and try to figure out which of them
> > break(s) things.
> > 
> > Thanks,
> > Rafael
> > 
> > ---
> >  drivers/base/power/common.c |    6 +++++-
> >  1 file changed, 5 insertions(+), 1 deletion(-)
> > 
> > Index: linux-2.6/drivers/base/power/common.c
> > ===================================================================
> > --- linux-2.6.orig/drivers/base/power/common.c
> > +++ linux-2.6/drivers/base/power/common.c
> > @@ -32,7 +32,11 @@ void device_pm_add(struct device *dev)
> >  	pr_debug("PM: Adding info for %s:%s\n",
> >  		 dev->bus ? dev->bus->name : "No Bus",
> >  		 kobject_name(&dev->kobj));
> > -	pm_link_add(dev, dev->parent);
> > +	if (dev->parent) {
> > +		pm_link_add(dev, dev->parent);
> > +		if (dev->parent->power.async_suspend)
> > +			dev->power.async_suspend = true;
> > +	}
> 
> to use this, we must make sure that device_enable_async_suspend is
> called before any of its child device being registered, right?
> should we check this in device_enable_async_suspend?
> or at least we should add the comments stating this issue.

That's correct in general, but I added the patch for testing purposes only.

The goal still is to identify all of the dependencies that need to be taken
care of and to represent them appropriately, so that we can safely set
async_suspend for all devices.

I wonder if you get any improvement with this patch applied?

Thanks,
Rafael
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