Re: Threading...

[Bill Davidsen]

Brian McGrew wrote:
> On 1/19/07 10:55 AM, "Arjan van de Ven" <arjan@xxxxxxxxxxxxx> wrote:
> > On Fri, 2007-01-19 at 10:43 -0800, Brian McGrew wrote:
> > > I have a very interesting question about something that we're seeing
> > > happening with threading between Fedora Core 3 and Fedora Core 5.  Running
> > > on Dell PowerEdge 1800 Hardware with a Xeon processor with hyper-threading
> > > turned on.  Both systems are using a 2.6.16.16 kernel (MVP al la special).
> > >
> > > We have a multithreaded application that starts two worker threads.  On
> > > Fedora Core 3 both of these we use getpid() to get the PID of the thread and
> > > then use set_afinity to assign each thread to it's own CPU.  Both threads
> > > run almost symmetrically even on their given CPU watching the system
> > > monitor.
> > this is odd; even in FC3 getpid() is supposed to return the process ID
> > not the thread ID
> >
> > > What am I missing?  What do I need to do in FC5 or the kernel or the
> > > threading library to get my threads to run in symmetric parallel again???
> > you should fix the app to use something like pthread_self() instead...
> > (or the highly unportable gettid() but that would just be horrible)
> -----
>
> And on FC5 I am using pthread_self but my problem isn't simply with
> pthread_self, it's with the scheduling.  On FC3 both threads run
> simultaneously in almost symmetric parallel.  On FC5 one thread don't pick
> up and start until the previous one is done.  On FC3, using getpid for the
> thread I could use set_afinity to force each thread to its own processor and
> with FC5 I can't; so I've got one idle processor all the time.
This sounds so unlikely I hesitate to mention it, but you are not, by 
any chance, running pthreads on one and nptl on the other, are you?

--
bill davidsen <davidsen@xxxxxxx>
  CTO TMR Associates, Inc
  Doing interesting things with small computers since 1979
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