Re: [RFC PATCH(Experimental) 0/4] Freezer based Cpu-hotplug

[Gautham R Shenoy <ego@in.ibm.com>]

On Thu, Feb 15, 2007 at 02:31:08PM +0100, Rafael J. Wysocki wrote:
> 
> So I think tonight I'll start adding try_to_freeze() to the kernel threads that
> set PF_NOFREEZE.

cool! While you are at it, let me try to enhance the freezer api's
to incorporate the PFE_* flags.

> > 
> > That would still mean going over the task list twice.
> 
> Yes, but I think this is inevitable anyway, because we have moved the
> disabling of nonboot CPUs after the suspending of devices (for
> ACPI-related reasons).
> 
> Currently, we have, roughly:
> 
> freeze_processes();
> shrink_memory(); (swsusp only)
> suspend_devices();
> disable_nonboot_cpus();
> suspend
> 
> and the reverse during the resume.
> 
> Still, the second pass will be quick, since the majority of tasks are frozen
> when disable_nonboot_cpus() is called.

Ok. That's fine by me. Lets get it working first. We can always optimize
it later :-)

> > 
> > Cool! Lets get started then ;-)
> 
> No problem with that. ;-)
> 
> Speaking of the classification, do you think it would be practical to use
> some kind of "freezing levels"?  I mean, for each task we can define the
> "freezing level" at which it should be frozen and each user of the freezer
> can call it with a specific "freezing level" as a parameter.  Of course for
> this purpose the tasks frozen at level 1 have to be a subset of the tasks
> frozen at level 2 etc. and I'm not sure if this requirement can be satisfied.

A freeze hierarchy! I hope this freeze_level parameter ain't an alternative
to the PFE_* flags because then a task would be in a dilemma as to
what freezing level it should be at, if it wants to be frozen for lets
say kprobes but not for cpu-hotplug. Cpu-hotplug and kprobes
may not have a dependency like the one that exists between cpu-hotplug
and suspend. So, at this moment, even I am not sure if there is a
need for the hierarchy.

> 
> Rafael

Thanks and Regards
gautham.

-- 
Gautham R Shenoy
Linux Technology Center
IBM India.
"Freedom comes with a price tag of responsibility, which is still a bargain,
because Freedom is priceless!"