Date: Tue, 31 Jul 2001 16:48:02 -0400 (EDT) From: Daniel Eischen <eischen@vigrid.com> To: Julian Elischer <julian@elischer.org> Cc: arch@FreeBSD.ORG Subject: Re: thread scheduling question Message-ID: <Pine.SUN.3.91.1010731163310.14566A-100000@pcnet1.pcnet.com> In-Reply-To: <Pine.BSF.4.21.0107311525440.35786-100000@InterJet.elischer.org>
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On Tue, 31 Jul 2001, Julian Elischer wrote:
> Does anyone have any views on what happens when
> the posix scheduling calls are applied against a multithreaded
> process?
What POSIX scheduling calls? sched_xxx?
> in particular against one with several KSEGRPs?
> are the multiple KSEs and KSEGRPs visible to the outside at all?
In general, I think that the sched_xxx (say, sched_setscheduler)
should apply to the process' main (original) KSE Group and not
affect other KSE Groups created for scope system threads. We'll
have another system call (perhaps later on) to allow changing of
those KSE Groups (Solaris has priocntl(2) to allow changing scheduling
parameters by PID, LWPID, PPID, PGID, etc).
Here's what Solaris 8 has to say about sched_setscheduler (and it's
mostly verbatim from what SUSv2 has to say):
The effect of this function on individual threads is depen-
dent on the scheduling contention scope of the threads:
o For threads with system scheduling contention scope,
these functions have no effect on their scheduling.
o For threads with process scheduling contention scope,
the threads' scheduling parameters will not be
affected. However, the scheduling of these threads
with respect to threads in other processes may be
dependent on the scheduling parameters of their pro-
cess, which are governed using these functions.
If an implementation supports a two-level scheduling model
in which library threads are multiplexed on top of several
kernel scheduled entities, then the underlying kernel
scheduled entities for the system contention scope threads
will not be affected by these functions.
The underlying kernel scheduled entities for the process
contention scope threads will have their scheduling parame-
ters changed to the value specified in param. Kernel
scheduled entities for use by process contention scope
threads that are created after this call completes inherit
their scheduling policy and associated scheduling parameters
from the process.
This function is not atomic with respect to other threads in
the process. Threads are allowed to continue to execute
while this function call is in the process of changing the
scheduling policy for the underlying kernel scheduled enti-
ties used by the process contention scope threads.
--
Dan Eischen
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