Massively parallel on single core? Post: 302395115

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Special Forums UNIX and Linux Applications High Performance Computing Massively parallel on single core? Post 302395115 by Andre_Merzky on Monday 15th of February 2010 04:23:34 AM

02-15-2010

Registered User

Hi Neo,

thanks for your reply!

I agree abut your remark as distributed architectures. This is my day-job, and I like it a lot :-)

I did not make the problem clear enough I think: the workload I am talking about are mostly idle jobs, so the CPU and memory load for each job is *very* low. Yes, I can beat the problem with more cores or nodes, but that seems very much like a waste, as those would be all idling most of the time.

Assume you plan for 1000 threads per core, and use quad code nodes - that would require 25 nodes which all idle all day long :-(

Some more detail, if that helps: the idle processes/threads are basically watchers, which represent a CPU/Memory heavy remote job they spawned, and whose state they are watching. Only when that state changes they become active, and kick of data movements or spawn new jobs.

We can't control the design of the remote job startup API very well (third party, synchronous API only), thus our technical options for obtaining state information about those jobs are limited, and boil down to

Code:

void * run_job (void * data)
{
   // this call runs a remote job, and blocks for hours
   remote_api_call (data);
   store_output_data (data);
}

#define NJOBS 100000

int main ()
{
  pthread_t threads[NJOBS]
  for ( int i = 0; i < NJOBS; i++ )
  {
     pthread_create (threads[i],  run_job, ...)
  }

  for ( int i = 0; i < NJOBS; i++ )
  {
     pthread_join (threads[i]);
  }
}

So, I can throw 25 nodes on that large for loop, and that is what we do basically - but what a waste...

The *real* workload are 100.000 CPU/Memory heavy remote jobs, which have sufficient resources to run concurrently. I am talking about the management side (our workflow engine).

Thanks, Andre.

Andre_Merzky

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LEARN ABOUT BSD

savecore

SAVECORE(8)						      System Manager's Manual						       SAVECORE(8)

NAME

       savecore - save a core dump of the operating system

SYNOPSIS

       savecore dirname [ system ]

DESCRIPTION

       Savecore  is  meant to be called at the end of the /etc/rc file.  Its function is to save the core dump of the system (if one was made) and
       to write a reboot message in the shutdown log.

       It saves the core image in the file dirname/core.n and its corresponding namelist in dirname/unix.n.  The second argument is  the  namelist
       for the system which made the core image; the current system is always assumed to be /unix.  The trailing ".n" in the pathnames is replaced
       by a number which grows every time savecore is run in that directory.

       Before savecore writes out a core image, it reads a number from the file dirname/minfree.  If there are fewer free blocks on the file  sys-
       tem  which contains dirname than the number obtained from the minfree file, the core dump is not done.  If the minfree file does not exist,
       savecore always writes out the core file (assuming that a core dump was taken).

       Savecore also writes a reboot message in the shut down log.  If the system crashed as a result of  a  panic,  savecore  records	the  panic
       string in the shut down log too.

       If  savecore detects that the system time is wrong because of a crash (the time in the core image is after the current time), it will reset
       the system time to its best estimate of the time, which is the time in the core image plus the elapsed time since the reboot.  It announces
       the time that it set when this occurs.

FILES

       /usr/adm/shutdownlogshutdown log
       /unix		   current UNIX

BUGS

       The method used to determine whether a dump is present, and to prevent the same core image from being saved multiple times, is not elegant.
       This information should be passed to init by the system; however, this is difficult because the system may have to  be  rebooted  a  second
       time if the root filesystem is patched.

3rd Berkeley Distribution													       SAVECORE(8)