On Thursday, 5 July 2007 02:43, Paul Mackerras wrote: > Miklos Szeredi writes: > > > OK, let me summarize the situation as I see it now: there are two > > camps, the pro-freezers and the anti-freezers. > > > > Pro-freezers say: > > > > - don't remove the freezer, otherwise we'll have to deal with > > numerous problems in drivers > > > > Anti-freezers say: > > > > - let's remove the freezer, which causes numerous problems > > > > Alan summerized the pro-freezer arguments well I think. What are the > > anti-freezer arguments then? > > 1. The freezer cannot be guaranteed deadlock-free without constructing > a dependency graph between tasks (both user and kernel), which is > virtually impossible since the dependencies are not externally > observable. I don't agree with that. The freezer only fails to handle uninterruptible tasks, so we need to take the situations in which an uninterruptible task waits for a frozen task into consideration. Now, if both tasks are from the user land, this is highly unusual. > 2. As a consequence of (1), we try to make a crude approximation of > the graph by saying "only kernel threads that want to be frozen > will be frozen" or some other similar statement. No. The rule is that kernel threads should not be freezable, but there are some for which that is useful. > 3. However, (2) means that we can no longer guarantee that drivers > will not get any I/O requests after their suspend method has been > called, and therefore the freezer fails in its main objective. This is a very general statement. Can you please give some examples? > 4. We have an existence proof that reliable suspend can be achieved > without the freezer. No. We only know that it might work if the nonboot CPUs are disabled before suspending devices, which is not the case in the generic suspend code. > To summarize, the argument is that the freezer is deadlock-prone and > ineffective. I remain unconvinced. ;-) Greetings, Rafael -- "Premature optimization is the root of all evil." - Donald Knuth _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
