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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mdm-run

MDM-RUN(1)							   User Commands							MDM-RUN(1)

NAME

       mdm-run - run a command in parallel with mdm-master

SYNOPSIS

       mdm-run command
       mdm-sync command

DESCRIPTION

       mdm-run	annotates  command  as	a  candidate  for parallel execution.  If an mdm-master process is present (i.e., the environment variable
       MDM_CMD_SOCK is defined), mdm-run submits command to the mdm-master, and it exits when the  master  issues  the	command  to  an  mdm-slave
       process	(which may be connected to another terminal) for execution.  mdm-sync runs command in place, but it coordinates with mdm-master to
       ensure that executing command does not interfere with commands that are currently executing in parallel.

       If there is no mdm-master process present (i.e., the environment variable MDM_CMD_SOCK is not defined), both mdm-run  and  mdm-sync  simply
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OPTIONS

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EXIT STATUS

       If  there is no mdm-master process present, the exit status of mdm-run is the exit status of command.  If an mdm-master process is present,
       the exit status is 0 if and only if command is successfully issued to an mdm-slave process for execution.

       The exit status of mdm-sync is always the exit status of command.

ENVIRONMENT

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EXAMPLE

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SEE ALSO

       mdm.screen(1)

Linux								    2009-03-06								MDM-RUN(1)