Date:	Sat, 28 Feb 2009 15:38:00 -0800
From:	Arve Hjønnevåg <arve@...roid.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Pavel Machek <pavel@....cz>,
	Alan Stern <stern@...land.harvard.edu>,
	"Woodruff, Richard" <r-woodruff2@...com>,
	Arjan van de Ven <arjan@...radead.org>,
	Kyle Moffett <kyle@...fetthome.net>,
	Oliver Neukum <oliver@...kum.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Nigel Cunningham <nigel@...el.suspend2.net>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	mark gross <mgross@...ux.intel.com>,
	Uli Luckas <u.luckas@...d.de>,
	Igor Stoppa <igor.stoppa@...ia.com>,
	Brian Swetland <swetland@...gle.com>,
	Len Brown <lenb@...nel.org>
Subject: Re: [RFD] Automatic suspend

On Sat, Feb 28, 2009 at 2:53 PM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> On Saturday 28 February 2009, Arve Hjønnevåg wrote:
>> Can you summarize what the problems with my current api are? I get the
>> impression that you think the overhead of using a list is too high,
>> and that timeout support should be removed because you think all
>> drivers that use it are broken.
>
> In no particular order:
> 1. One user space process can create an unlimited number of wakelocks.  This
>   shouldn't be possible.  Moreover, it is not even necessary for any process
>   to have more than one wakelock held at any time.

This has been addressed. A user space process cannot create more
wakelocks than it has filedescriptors.

> 2. Timeouts are wrong, because they don't really _solve_ any problem.  They are
>   useful for working around the fact that you can't or you don't want to
>   modify every piece of code that in principle should take a wakelock and
>   that's it.

Yes, timeouts are sometimes wrong, but they are not always wrong. I
gave two examples where the use of timeouts was not incorrect.

>  However,  entire concept of having one code path acting on
>   behalf of another one on a hunch that it might be doing something making
>   suspend undesirable is conceptually broken IMO.

OK. Do you have an alternative?

I my opinion this is how the entire system works if you do autosuspend
without a mechanism like wakelocks.

> 3. The overhead of using a list is unnecessary and _therefore_ too high (not
>   just too high).

It is only unnecessary if you do not want accounting or timeouts. The
overhead of a timer going off when it is not needed (if you push
timeouts to the drivers) is way higher then the overhead putting
wakelocks on a list.

> 4. There seems to be a race between user space wakelocks and the freezer
>   (perhaps I overlooked something, in which case please disregard this item).

You are missing something. Wakelocks overlap.

> 5. The name "wakelocks" is confusing, because they aren't locks and they
>   affect suspend, not wake.

I can change the name. Currently suspend_blocker seems to be
acceptable many people, but some don't like this name either.

> 6. Last time I saw the patches they were barely commented and the changelogs
>   didn't describe the code well (if at all).

I have not added many inline comments, but I did add the kerneldoc
comments you requested, and a lot of documentation since the first
patches.

> 7. There's no clear distinction between debug/stats code and the basic
>   functionality.

I don't think this is still true.

-- 
Arve Hjønnevåg
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