Some specific questions about 5.x

[Lev Walkin]

Miguel Mendez wrote:
> 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.


What about Solaris' migration towards 1:1 model from the N:M one they
had supported for years already? Who are insane, Solaris folks (moving
towards Linux) or Free/NetBSD ones (migrating to the old Solaris'
behavior)?


-- 
Lev Walkin
vlm at netli.com