Massively parallel on single core? Post: 302394358

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Special Forums UNIX and Linux Applications High Performance Computing Massively parallel on single core? Post 302394358 by Andre_Merzky on Thursday 11th of February 2010 07:48:20 AM

02-11-2010

Registered User

Massively parallel on single core?

Hia all,

I am not sure how many people actually follow the HPC forum on unix.com, but you may be interested in discussing the following (academic) problem:

Assume you want to run a *very* large number (say 100.000) of very lightweight synchronous operations. As an example, assume that you want to run 100.000 instances of

Code:

sleep (3600); // thats one hour sleep

The trivial (aka braindead) approach would be

Code:

for ( int i = 0; i < 100000; i++ )
{
  ::sleep (3600);
}

Takes about 15 years to finish ;-)

One could start 1000 threads, and run a sleep in each of them. That reduces the runtime to 100 hours - still 4 days, and the system is totally idle all the time.

So, using more threads? Won't work, as the max-threads-per-process limit will be hit at some point.

So, spawn 100 processes which spawn 1000 threads each?
The max-threads-per-process limit is, on Linux, close to the max-threads-per-system limit, so that won't work. On other Unixes that is different, but I don't think you get 100.000 threads on a normal single CPU system. Do you?

So, what would your approach be?

I am not looking for a sleep replacement: so saying that I should set alarm or something similar is of not much use. Sleep is obviously only an example here - replace it with an extremely lightweight job, like running a very time consuming synchronous remote operation.

I am looking forward to the ideas you guys can come up with! :-)

Cheers, Andre.

Last edited by Andre_Merzky; 02-11-2010 at 08:48 AM.. Reason: layout...

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abrt-action-generate-core-backtrace

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NAME

       abrt-action-generate-core-backtrace - Generates coredump-level backtrace

SYNOPSIS

       abrt-action-generate-core-backtrace [-v] [-r] [-d DIR]

DESCRIPTION

       This tool uses coredump from the file coredump and binary at the path stored in file executable in the problem directory to generate
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       Coredump-level backtrace resembles ordinary backtrace in that it contains information about call frames present on the stack at the time of
       the crash. However, it only contains information that can be obtained from the coredump without debugging symbols available - mainly
       relative addresses of the stored instruction pointers. Such backtrace can still be useful for reporting and reproducing the bug and does
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       The result is saved in the problem directory in a file named core_backtrace.

   Integration with libreport events
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		   abrt-action-generate-core-backtrace

OPTIONS

       -d DIR
	   Path to problem directory.

       -r
	   Do not hash function fingerprints. Useful for debugging.

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