Linux-kernel mailing list archive 2000-40,: Re: Weightless process class

# Re: Weightless process class

Rik van Riel (riel@conectiva.com.br)
Wed, 4 Oct 2000 16:16:22 -0300 (BRST)

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On Wed, 4 Oct 2000, LA Walsh wrote:

> I had another thought regarding resource scheduling -- has the
> idea of a "weightless" process been brought up?

Yes, look for "idle priority", etc..
It also turned out to have some problems ...

> Weightless means it doesn't count toward 'load' and the class
> strictly has lowest priority in the system and gets *no* CPU
> unless there are "idle" cycles. So even a process niced to -19
> could CPU starve a weightless process.

One problem here is that you might end up with a weightless
process having grabbed a superblock lock, after which a
normal priority CPU hog kicks in and starves the weightless
process.

The result is that that superblock lock never gets released,
and everybody needing to grab that lock blocks forever, even
if they have a higher priority than the CPU hog that's starving
our idle process...

The solution to this would be only starve these processes
when they are in user space and can no longer be holding
any kernel locks.

Do we have something like an in_kernel(proc) macro ???

> Perhaps if memory was needed, the paging code would page out
> weightless processes first... etc?...

This makes little sense. If the system doesn't page out
the least used page in the system, the disks will be more
busy on page faults than they need to be, taking away IO
bandwidth from more important processes ;)

regards,

Rik

    --
    "What you're running that piece of shit Gnome?!?!"
           -- Miguel de Icaza, UKUUG 2000

    http://www.conectiva.com/		http://www.surriel.com/

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