linux-kernel - Re: Hibernation Redesign

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Message-Id: <200707112217.19220.nigel@nigel.suspend2.net>
Date:	Wed, 11 Jul 2007 22:17:18 +1000
From:	Nigel Cunningham <nigel@...el.suspend2.net>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	rjw@...k.pl, a1426z@...ab.com, jeremy@...p.org, jbms@....edu,
	pavel@....cz, nickpiggin@...oo.com.au,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org
Subject: Re: Hibernation Redesign

Hi.

On Wednesday 11 July 2007 22:09:39 Miklos Szeredi wrote:
> > > Freezing of tasks is slowing down suspend.  Don't know how serious
> > > this is, suspend is pretty fast, but could possibly be even faster.
> > 
> > It's FUD. Freezing of tasks normally takes next to no time. I've never 
> > understood the rediculously long timeout it has. If freezing succeeds, all 
> > processes are frozen within 1/2 a second tops. If it fails, nothing is 
going 
> > to change in the following 19.5 seconds (or whatever it is if I don't 
> > remember the value properly).
> 
> Right.  The 20s timeout is again a sign of brokenness.
> 
> If we expect something to fail, it should fail immediately, without
> waiting for arbitrary timeouts.
> 
> And if we don't expect it to fail, why the timeout?

Two reasons:

1) The processing does take time. We're sending (pseudo-)signals to other 
processes, and the amount of time it will take for them to enter the 
refrigerator will depend upon the number of processes there are, the 
scheduling algorithm being used, the rate at which they're forking and what 
other activity is occuring. That's why I said "normally" above.

2) Things do get broken. New functionality gets added which sometimes doesn't 
immediately play well with the freezer. In such cases, we want to fail nicely 
rather than wrongly assuming it will always work and waiting indefinitely.

Regards,

Nigel
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