Message-ID: <42411CAC.5000808@yahoo.com.au>
Date: Wed, 23 Mar 2005 18:37:16 +1100
From: Nick Piggin <nickpiggin@yahoo.com.au>
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To: Arun Srinivas <getarunsri@hotmail.com>
CC: linux-kernel@vger.kernel.org
Subject: Re: help needed pls. scheduler(kernel 2.6) + hyperthreaded related
 questions?
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Arun Srinivas wrote:
> If the SMT (apart from SMP) support is enabled in the  .config file, 
> does the kernel recogonize the 2 logical processor as 2 logical or 2 
> physical processors?
> 

You shouldn't be able to select SMT if SMP is not enabled.
If SMT and SMP is selected, then the scheduler will recognise
the 2 processors as logical ones.

> Also, as the hyperthreaded processor may schedule 2 threads in the 2 
> logical cpu's, and it may not necessarily be form the same process i.e., 
> the 2 thread it schedules may be from the same or from the different 
> process.
> 

Yes.

> So, is there any way I can tell the scheduler (assuming I make the 
> scheduler recogonize my 2 threads..i.e., it knows their pid) to schedule 
> always my 2 threads @ the same time? How do I go abt it?
> 

Use sched_setaffinity to force each thread onto the particular
CPU. Use sched_setscheduler to acquire a realtime scheduling
policy. Then use mutexes to synchronise your threads so they
run the desired code segment at the same time.

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