Re: Comments on the KSE option

On Fri, 2006-10-27 at 18:25 -0700, Julian Elischer wrote:
> Alexandre "Sunny" Kovalenko wrote:
> > On Fri, 2006-10-27 at 16:41 -0400, Daniel Eischen wrote:
> >> On Fri, 27 Oct 2006, Paul Allen wrote:
> >>
> >>>> From Julian Elischer <julian_at_elischer.org>, Fri, Oct 27, 2006 at 12:27:14PM -0700:
> >>>> The aim of the fair scheduling code is to ensure that if you, as a user,
> >>>> make a process that starts 1000 threads, and I as a user, make an
> >>>> unthreaded process, then I can still get to the CPU at somewhat similar
> >>>> rates to you.  A naive scheduler would give you 1000 cpu slots and me 1.
> >>> Ah.  Let me be one of the first to take a crack at attacking this idea as
> >>> a mistake.
> >> No, it is POSIX.  You, the application, can write a program with
> >> system scope or process scope threads and get whatever you behavior
> >> you want, within rlimits of course.
> >>
> >> If you want unfair scheduling, then create your threads with
> >> system scope contention, otherwise use process scope.  The
> >> kernel should be designed to allow both, and have adjustable
> >> limits in place for (at least) system scope threads.
> >>
> >> Noone is saying that you can't have as many system scope threads
> >> as you want (and as allowed by limits), just that you must also
> >> be able to have process scope threads (with probably higher limits
> >> or possibly no limits).
> >>
> > I might be missing something here, but OP was separating M:N (which is
> > what you are referring to above), and "fairness" (not giving process
> > with 1000 *system scope* threads 1000 CPU scheduling slots). As far as I
> > know the first one is POSIX and the second one is not. 
> > 
> > FWIW: as an application programmer who spent considerable amount of time
> > lately trying to make heavily multithreaded application run most
> > efficiently on 32-way machine, I would rather not have to deal with
> > "fairness" -- M:N is bad enough.
> > 
> 
> 
> no,  fairness is making sure that 1000 process scope threads
> do not negatively impact other processes.
> 1000 system  scope threads are controlled by your ulimit settings
> (Each one counts as a process.)
> 
> 
I apologize for misinterpreting your words. But then, if I have M:N set
to 10:1, I would expect application with 1000 process scope threads to
have as many CPU slots as 100 processes, or, if I have 10 system scope
threads and 990 process scope threads, I would expect application to
have as many CPU slots as 109 processes. Is this what you refer to as
"fairness"? 

-- 
Alexandre "Sunny" Kovalenko