kernel threads

[Lari Sihto]

Ok, thanks for the clarification.

ti 24. marrask. 2020 klo 4.42 Kevin P. Neal (kpn at neutralgood.org) kirjoitti:

> On Mon, Nov 23, 2020 at 07:17:50AM +0200, Lari Sihto wrote:
> > Yes, that's it. Do you know why the top half is allowed to sleep but the
> > bottom half is not?
>
> The bottom half is hardware interrupt driven. The top half is entered via
> system calls or traps on behalf of the process/thread. If you have a
> process
> or thread context you can sleep and therefore yield to another process or
> thread. Interrupts don't have that luxury. The bottom half isn't part of
> any process or thread. So no sleeping is allowed in the bottom half.
>
> > ma 23. marrask. 2020 klo 0.01 Kevin P. Neal (kpn at neutralgood.org)
> kirjoitti:
> >
> > > On Sun, Nov 22, 2020 at 09:59:57PM +0200, Lari Sihto wrote:
> > > > Hi, just wondering if there is some technical or philosophical
> reason as
> > > to
> > > > why the freebsd operating system doesn't seem to use kernel-space
> threads
> > > > like some other unix-like operating systems do. To my knowledge the
> need
> > > > for kernel threads arises when the kernel code needs to sleep in
> kernel
> > > > which one cannot do. Kernel threads seem to fix that problem. Have
> been
> > > > wondering this for a long time and I hope someone here knows the
> > > reasoning
> > > > behind this implementation detail be it just performance related or
> > > > something along the line of "no-one just haven't been up to
> implementing
> > > > that kind of a functionality"?
> > >
> > > Are you thinking of something different than what is described in the
> > > kthread(9) and kproc(9) man pages?
> > >
> > > Also, my limited understanding is that the "top" half of the kernel is
> > > allowed to sleep, but the "bottom" half is not.
> > >
> > > You'll get more informed responses to this topic on the freebsd-arch,
> > > freebsd-hackers, or maybe freebsd-current lists. Very few if any kernel
> > > hackers hang out on this list.
> --
> Kevin P. Neal                                http://www.pobox.com/~kpn/
>
> Seen on bottom of IBM part number 1887724:
> DO NOT EXPOSE MOUSE PAD TO DIRECT SUNLIGHT FOR EXTENDED PERIODS OF TIME.
>