linux-kernel - Re: [PATCH 2/6] PM: Asynchronous resume of devices

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Message-Id: <200908292117.06049.rjw@sisk.pl>
Date:	Sat, 29 Aug 2009 21:17:05 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	"linux-pm" <linux-pm@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>, Len Brown <lenb@...nel.org>,
	Pavel Machek <pavel@....cz>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Zhang Rui <rui.zhang@...el.com>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Linux PCI <linux-pci@...r.kernel.org>
Subject: Re: [PATCH 2/6] PM: Asynchronous resume of devices

On Saturday 29 August 2009, Rafael J. Wysocki wrote:
> On Saturday 29 August 2009, Alan Stern wrote:
...
> > Strictly speaking, a new thread should be started only when needed.  
> > That is, only when all the existing threads are busy running a 
> > callback.  It shouldn't be too hard to keep track of when that happens.
> 
> The async framework does that for us. :-)

So, when I said "async threads", I should have rather said "async functions",
because one async thread can execute multiple functions scheduled with
async_schedule().

Taking that into consideration, it all works like this.  When there's a new
async device to handle and there are no async threads available, a new thread
is started and it runs the async function that handles the device and
"opportunistically" searches dpm_list (once) for other device that are ready
for handling.  After this function has returned, the thread goes to sleep and
it only exits after being idle for 1 s.  In turn, when there's a new async
device to handle and there are async threads available, on of them gets the
async function to run.

I don't really think we can do much better than this in any other approach.

Thanks,
Rafael
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