Subj : Re: threads do not get cpa
To   : comp.programming.threads,comp.sys.sgi.misc
From : azb123
Date : Mon Aug 08 2005 06:14 am

loic-dev@gmx.net wrote:
> Salut Markus,
>
> > However, the original question still remains: the number of processors
> > the program runs on seems unpredictable (at least to me), even after I
> > have added the pthread_setconcurrency() call. When I create 3 threads,
> > the program sometimes gets 3 processors, and sometimes just 1 (the SGI
> > is still mostly empty).
> >
> > Is there anything known about the way the number of processors to be
> > used is determined under IRIX 6.5.24m?
>
> I don't have access to a SGI machine, so I can't verify in the
> practice... However, accordingly to the a manual about IRIX
> programming, I read:
>
> <copy>
> You can specify an initial thread scheduling scope by calling
> pthread_attr_setscope() and passing one of the scope constants
> (PTHREAD_SCOPE_SYSTEM or PTHREAD_SCOPE_PROCESS) in the pthread_attr_t
> object. By default, process scope is selected and scheduling is
> performed by the thread runtime, but thread scheduling by the kernel is
> provided with the system scope attribute. System scope threads run at
> real-time policy and priority and may be created only by privileged
> users.
> </copy>
>
> You may need to select system contention scope (PTHREAD_SCOPE_SYSTEM)
> to obtain the wanted bahavior.

Hi Loic,

yes, PTHREAD_SCOPE_SYSTEM sounds like it would be the solution.
However, threads with scheduling scope PTHREAD_SCOPE_SYSTEM require
under IRIX to be run as root or with scheduling management
capabilities, since with this scope you can have (under IRIX) threads
with a priority higher than system daemons. Therefore, this scheduling
scope is not available to me.

There is another, non-portable, scheduling scope available under IRIX
(PTHREAD_SCOPE_BOUND_NP), but that shows the same behavior, i.e. the
cpu-usage seems to be erratic and unpredictable (at least for me).

Markus

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