linux-kernel - Re: Threading...

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Date:	Fri, 19 Jan 2007 16:26:38 -0500
From:	Bill Davidsen <davidsen@....com>
To:	Brian McGrew <brian@...ionpro.com>
CC:	linux-kernel@...r.kernel.org, fedora-users@...at.com
Subject: Re: Threading...

Brian McGrew wrote:
> On 1/19/07 10:55 AM, "Arjan van de Ven" <arjan@...radead.org> 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@....com>
   CTO TMR Associates, Inc
   Doing interesting things with small computers since 1979
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