Re: scheduler support to lock user processes out?

[David Young <dyoung%pobox.com@localhost>]

On Mon, Feb 18, 2008 at 08:19:29PM +0100, Matthias Drochner wrote:
> > I don't think that fixed policies such as, "the system may cancel
> > user-requested suspension" or "users may not suspend drivers that are
> > in-use" belong in the kernel.
> 
> That's not policy, that's a technical requirement imho.

I can show several examples why it is not a technical requirement. :-)
I routinely suspend several devices that are in-use, including ethernet
& WLAN NICs, and I have even suspended the HDD where root is mounted.
The other day I patched the floppy driver so that I can suspend it;
an interesting side-effect is that I can suspend and resume it while I
format a disk.

> > We already do suspend devices that are in-use.
> > [...]
> 
> Yes, but it has shown that it is necessary to keep other
> processes out. Which is pretty well done by switching
> secondary CPUs offline, except some corner cases, as I wrote
> in my original mail.
> This is fine in a global system suspend situation, but
> not acceptable at runtime.

I am not sure we are understanding each other.  I think that if it
is not acceptable to you that devices should suspend while userland
keeps running, then you may need to apply a different policy than I do.
PMF is flexible enough that you can have it either way, and PMF gets
more flexible all of the time.

Dave

-- 
David Young             OJC Technologies
dyoung%ojctech.com@localhost      Urbana, IL * (217) 278-3933 ext 24