kernel threads

Lari Sihto lari.sihto at
Mon Nov 23 05:18:04 UTC 2020

Yes, that's it. Do you know why the top half is allowed to sleep but the
bottom half is not?

ma 23. marrask. 2020 klo 0.01 Kevin P. Neal (kpn at 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                      
> "Not even the dumbest terrorist would choose an encryption program that
>  allowed the U.S. government to hold the key." -- (Fortune magazine
>     is smarter than the US government, Oct 29 2001, page 196.)

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