Re: Weightless process class

[Matti Aarnio]

On Wed, Oct 04, 2000 at 06:16:57PM -0300, Rik van Riel wrote:
> > > ---
> > > 	One way would be to set a flag "I'm holding a lock" and when
> > > it releases the lock(s), deschedule it?
> > 
> > 	There is a well-known name for this -- priority inversion.
> > 
> > 	Implement the whole shebang of starvation avoidance tricks,
> > 	and we can whak the scheduler to group processes into separate
> > 	subsets, which in current system leads to starvation lockups.
> > 
> > 	A thing for 2.5 ?  (With possible backport to 2.4 latter.)
> 
> We don't need that.
> 
> We just need one boolean per thread ... is it holding a kernel
> lock or not?

	The BKL or *any* (kernel) lock ?

	For my knowledge there is no limitation on how many
	locks a thread can hold.  Having a single bool might
	not be enough.  A counter is better ?

	For example: Two filesystems are locking on their respective
	superblocks, and then they are locking on some underlying IO
	facility which both are sharing.

	Should the lock-count be incremented before the lock acquisition
	has happened, or only afterwards, that is other story.

> If it is, make sure its scheduling latency isn't too high.

	e.g. all processes having *any* locks are raised to the highest 
	possible class to make sure they are not starved out ?

> If it isn't holding any lock, we can do with it what we want,
> including completely starving the task for several seconds
> (or even minutes) if scheduling latency or VM pressure warrants
> it.

	Yes, that is obvious.

> regards,
> 
> Rik
> http://www.conectiva.com/		http://www.surriel.com/

/Matti Aarnio