Some specific questions about 5.x

[Miguel Mendez]

On Wed, 26 Mar 2003 10:57:07 +0300
Alex <alex at dynaweb.ru> wrote:

Howdy.

> 1.    Is it true that kernel threads are more "heavy" than userspace 
> ones (pthread) and hence application with hundreds of threads will
> work evidently slower than that using pthreads due to more switching
> penalties?

AFAIK, not in a hybrid model. Systems that do 1:1 thread mapping (Like
Gah! Nu/Linux) will suffer from this kind of situation, also will use
more kernel memory. In hybrid implementations based on Scheduler
Activations, like FreeBSD's KSE, and NetBSD's SA, there's a balance
between the number of kernel virtual processors available and the number
of userland threads, it's an N:M model. Nathan Williams' paper on the
subject suggests that context switch is not much slower than a pure
userland implementation. Also, keep in mind that pure userland has other
problems, like when one thread blocks on I/O. In pure userland threading
systems this means the whole process is blocked, whereas in KSE and SA
only that thread is stopped.

> 2.    Is it true that even 5.x has no implementation for inter-process
> semaphores that are blocking calling thread only not the whole process
> as usually in FreeBSD?

That I don't know, perhaps the local KSE guru, Julian might have an
answer for this.

Cheers,
-- 
        Miguel Mendez - flynn at energyhq.homeip.net
        GPG Public Key :: http://energyhq.homeip.net/files/pubkey.txt
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