(no subject)

[Ying Chen]

Hi,

I have two questions on Linux pthread related issues. Would anyone be able 
to help?

1. Does any one have some suggestions (pointers) on good kernel Linux thread 
libraries?
2. We ran multi-threaded application using Linux pthread library on 2-way 
SMP and UP intel platforms (with both 2.2 and 2.4 kernels). We see 
significant increase in context switching when moving from UP to SMP, and 
high CPU usage with no performance gain in turns of actual work being done 
when moving to SMP, despite the fact the benchmark we are running is 
CPU-bound. The kernel profiler indicates that the a lot of kernel CPU ticks 
went to scheduling and signaling overheads. Has anyone seen something like 
this before with pthread applications running on SMP platforms? Any 
suggestions or pointers on this subject?

Thanks a lot!

Ying



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Re: threads

[J . A . Magallon]

On 03.07 Ying Chen wrote:
> 2. We ran multi-threaded application using Linux pthread library on 2-way 
> SMP and UP intel platforms (with both 2.2 and 2.4 kernels). We see 
> significant increase in context switching when moving from UP to SMP, and 
> high CPU usage with no performance gain in turns of actual work being done 
> when moving to SMP, despite the fact the benchmark we are running is 
> CPU-bound. The kernel profiler indicates that the a lot of kernel CPU ticks 
> went to scheduling and signaling overheads. Has anyone seen something like 
> this before with pthread applications running on SMP platforms? Any 
> suggestions or pointers on this subject?
> 

Too much contention ? How frequently do you create and destroy threads ?
How much frequently do they access shared-writable-data ?
How do you protect them ?

It seems like your system spents more time creating and killing threads
that doing real work.

-- 
J.A. Magallon                                                      $> cd pub
mailto:jamagallon@able.es                                          $> more beer

Linux werewolf 2.4.2-ac13 #3 SMP Wed Mar 7 00:09:17 CET 2001 i686

Re: your mail

[Don Dugger]

Ying-

I'm a little confused here.  It's very hard to compare a UP application
vs. the same app. converted to use threads.  Unless the app. is
structured such that multiple threads can run at the same time then
no, you won't see any improvement by going to SMP, in fact a true
single threaded app. will frequently slow down when run on an SMP
kernel.

Have you watched a CPU meter while your benchmark runs?  Even something
basic like `top' should give you a feel for whether or not your
using all of the CPU's.


On Tue, Mar 06, 2001 at 03:55:55PM -0800, Ying Chen wrote:
> Hi,
> 
> I have two questions on Linux pthread related issues. Would anyone be able 
> to help?
> 
> ...
>
> 2. We ran multi-threaded application using Linux pthread library on 2-way 
> SMP and UP intel platforms (with both 2.2 and 2.4 kernels). We see 
> significant increase in context switching when moving from UP to SMP, and 
> high CPU usage with no performance gain in turns of actual work being done 
> when moving to SMP, despite the fact the benchmark we are running is 
> CPU-bound. The kernel profiler indicates that the a lot of kernel CPU ticks 
> went to scheduling and signaling overheads. Has anyone seen something like 
> this before with pthread applications running on SMP platforms? Any 
> suggestions or pointers on this subject?
> 
> Thanks a lot!
> 
> Ying
> 
> 
> 
> _________________________________________________________________
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> 
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-- 
Don Dugger
"Censeo Toto nos in Kansa esse decisse." - D. Gale
n0ano@valinux.com
Ph: 303/938-9838

Re: threads

[Reto Baettig]

lock_kernel is a special case and will not block when you call it in
order to create a new kernel thread. Look at the implementation of
lock_kernel if you have any doubts (this is true for the 2.2 kernels. I
don't know it by heart for the 2.4 kernel). 

	Reto

"M.Kiran Babu" wrote:
> 
>  sir,
> i got some doubts in kernel
> programming. i am using linux 6.1 version. i want to use threads in
> kernel.is it possible to use pthreads in kernel. there is one more
> function kernel_thread. can i use
> that function. if i use that function how to get synchonization. inmany
> files it was used. but everywhere lock_kernel() and unlock_kernel()
> functions are being used. if we use that commands the whole kernel gets
> locked. is there any other mechanisms. or can i use that methods only. if
> i can use these methods what is the syntax of kernel_thread function. the
> arguments that are passing to these function are 3. i dont know what are
> those three. please  tell me.
> 
> 
> 
> 
> 
> 
> -
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Re: threads

[Matti Aarnio]

On Fri, Nov 10, 2000 at 08:33:29PM +0530, M.Kiran Babu wrote:
>  sir,
> i got some doubts in kernel
> programming. i am using linux 6.1 version. i want to use threads in

	Linux kernel versions are now running up to 2.4.0*, what is
	that 6.1 ?  Some distribution ?  Which ?
	Which kernel version you are referring into ?

> kernel.is it possible to use pthreads in kernel. there is one more
                               ^^^^^^^^^^^^^^^^^^   NO.
> function kernel_thread.
> can i use that function.

	#include <asm/processor.h>

	extern pid_t kernel_thread(int (*fn)(void *), void * arg,
				   unsigned long flags);

> if i use that function how to get synchonization.

	With mutexes, waitqueues, or spinlocks.
	All kernel facilities.

> inmany files it was used. but everywhere lock_kernel() and unlock_kernel()
> functions are being used. if we use that commands the whole kernel gets
> locked.

	Really ?  Who says you need to   lock_kernel()  for starting
	a kernel thread ?

> is there any other mechanisms. or can i use that methods only.
> if i can use these methods what is the syntax of kernel_thread function.
> the arguments that are passing to these function are 3.
> i dont know what are those three. please tell me.

	Pick 2.4.0 sources, open them up.

	Then do:  "make psdocs" or "make pdfdocs" or "make htmldocs"
	and you get up documents from within the system into your
	source location Documentation/DocBook/  subdirectory.

	You propably want to study  kernel-hacking,  kernel-locking,
	and  kernel-api   documents.

	(Your system needs to have DocBook, related SGML tools, and
	 (for PS/PDF) (La)TeX subsystem.)

/Matti Aarnio
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threads

[M.Kiran Babu]

 sir,
i got some doubts in kernel
programming. i am using linux 6.1 version. i want to use threads in
kernel.is it possible to use pthreads in kernel. there is one more
function kernel_thread. can i use
that function. if i use that function how to get synchonization. inmany
files it was used. but everywhere lock_kernel() and unlock_kernel()
functions are being used. if we use that commands the whole kernel gets
locked. is there any other mechanisms. or can i use that methods only. if
i can use these methods what is the syntax of kernel_thread function. the
arguments that are passing to these function are 3. i dont know what are
those three. please  tell me.
				




                                               
                        
               




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