Re: [PATCH 3/9] PM: suspend_block: Abort task freezing if a suspend_blocker is active.

[Nigel Cunningham <ncunningham@crca.org.au>]

Hi.

On Thu, 2009-05-07 at 16:49 -0700, Arve Hjønnevåg wrote:
> On Thu, May 7, 2009 at 3:41 AM, Pavel Machek <pavel@ucw.cz> wrote:
> > If the code runs for 20 seconds, it is a bug to be fixed.
> 
> The code gives up after 20 seconds, it does not normally run for 20
> seconds. It is arguably a bug that it gives up after 20 seconds since
> the time required to freeze all the threads grows with the number of
> threads that are running. It could still be making progress after 20
> seconds. Since the time required to freeze all tasks is the number of
> tasks times the time it takes to interrupt each task there is no way
> to ensure that the time required is insignificant. If we do not abort
> task freezing when there is a wakeup event, then the worst case wakeup
> latency is guarantied to be worse than the worst case latency for any
> other uninterruptible kernel call.

I agree with Pavel here. If freezing takes 20 seconds, something is
wrong. (Remember that most tasks will not be running, and will therefore
respond to the pseudo-signal and freeze immediately).

In fact, I'd go further. In the thousands of times I've run the freezer
over the years, it has never taken more than 1 second - let alone 20 -
when freezing has been successful. A delay of 20 seconds was more
relevant when the value included the time for syncing data to disk.

Regards,

Nigel

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