Re: [RFD] Automatic suspend
From: Arve Hjønnevåg
Date: Sat Feb 28 2009 - 18:38:22 EST
On Sat, Feb 28, 2009 at 2:53 PM, Rafael J. Wysocki <rjw@xxxxxxx> 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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