RE: linux threads

["Nilanjan Roychowdhury" <Nilanjan.Roychowdhury@xxxxxxxx>]

-----Original Message-----
From: amith [mailto:amith@xxxxxxxxxxxxxxx] 
Sent: Monday, August 02, 2004 10:44 AM
To: Nilanjan Roychowdhury
Subject: Re: linux threads

Nilanjan Roychowdhury wrote:

>If I create two threads using pthread_create calls in linux does the kernel sees them as two schedulable entities ?? I can see two LWP with diff PIds.
>
yes. hence they have different PID's. But if u create user-space threads 
then it is seen by the kernel as one process and hence the time-slice 
for the process (which creaated the thread)  is divided between threads 
created by the process. Now, in this case (pthread) they are not 
user-space threads  (pthread -> kernel level threads) and hence each new 
thread gets a new time slice and runs on the CPU. Another advantage of 
using kernel-level threads like pthread is it takes advantage of SMP 
machines where a thread can be scheduled on a diff CPU. where as the 
user-level threads cannot run on different CPU's since they are not 
visible to the kernel as different processes (or entities to be 
shceduled) . in case you want to try both kernel -level  and user-space 
threads there are 2 libraries available.Use pthreads for kernel threads 
or GNU Portable Threads  (Pth) for user space threads.

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>Secondly lets say if I create a thread in process A create another thread in process B then can I control the scheduling between them. 
>
scheduling between threads in different unrelated processes ??
Yes I mean scheduling between threads in two diff processes. Like currently I am executing thread 1 from process A and then I attach my execution ( definitely after blocking the prev thread) to thread 2 from process B . Is it possible ???

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>Basically the kernel scheduler is thread aware or not?? 
>
yes it is. it depends on what u mean by thread aware actually ;-) !

By "thread aware" I mean threads should be visible to the scheduler.

cheers,
Amith

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