Hi,

Here is what I have now:


if ($QueuedJobs > 0) {
    my $TCPU = ( $MaxRunningJobs < $TotalCPU ) ? $MaxRunningJobs : 
$TotalCPU;
    $MaxTime=(($TotalJobs * $WallTime) - $UsedTime) / $TCPU;
    if ( $MaxTime < 0){
       $MaxTime=99999999;
    }
} else {
    $MaxTime = 0;
}


David McBride wrote:
> On Fri, 2005-12-16 at 11:04 +0100, Jeff Templon wrote:
> 
> Hi Jeff,
> 
> 
>>my $TCPU = ( $MaxRunningJobs < $TotalCPU )? $MaxRunningJobs : $TotalCPU;
>>$MaxTime=(($TotalJobs * $WallTime) - $UsedTime) / $TCPU;
>>if ( $MaxTime < 0){
>>      $MaxTime=99999999;
>>  }
> 
> 
> Okay, this code would, when tidied up, look equivilent to this:
> 
> # -------8<------------------------------------------------------------
> 
> # Work out how many CPUs are available to service jobs in this queue.
> my $avail_cpus;
> if ($MaxRunningJobs < $TotalCPU) {
> 	# Only $MaxRunningJobs may run on this queue, despite the fact
> 	# we have more CPUs than jobs available.
> 	$avail_cpus = $MaxRunningJobs;
> }
> else {
> 	# The total number of CPUs on the cluster is our limiting 
> 	# factor.
> 	$avail_cpus = $TotalCPU;
> }
> 
> # Calculate the worst-case reponse time.  In this simple model, every
> # job is expected to run right up it's wall_clock limit.  
> # Once we have the maximum serial-runtime of *all* of the jobs 
> # currently queued or running, we divide that by the number of CPUs 
> # available to service jobs in this queue.
> 
> my $wrt;	# Our calculated worst-case-response time.
> 
> # We assume that each job will take $WallTime to run.  However,
> # we need to subtract the current total accumulated runtime of those
> # jobs already running to account for the fact that they have already 
> # used some of their allotted time.
> my $serial_runtime = ($TotalJobs * $WallTime) - $UsedTime.
> 
> # Now that we have the serial runtime of all currently running and 
> # queuing jobs, we divide that by the number of available CPUs.
> $wrt = $serial_runtime / $avail_cpus;
> 
> # Fudge: If, somehow, we've miscalculated and gotten a negative 
> # worst-case response time, reset $wrt to A Large Number.
> if ($wrt < 0) {	$wrt = 99999999 };
> 
> # Our estimated response time is simply half our worst-case response 
> # time.
> 
> # -------8<------------------------------------------------------------
> 
> (I haven't tested any of the above, there might be minor syntatical
> errors.)
> 
> 
>>I am going to make the change to QueuedJobs by hand here until I hear 
>>something different.  Hmm, on second thought that is even worse, since 
>>MaxTime will be less than zero, so all ERTs will be huge.
> 
> 
> You don't want to do that.  The code is trying to work out the
> worst-case runtime of every single job, queued and running.  The upper
> limit on all of these jobs is clearly the wall-clock time limit.  
> 
> So, you need to work out how long the *current* jobs can run for -- ie:
> 
> 	($RunningJobs * $WallTime) - $UsedTime
> 
> [ Where $RunningJobs == the number of jobs currently running on the
> cluster.  This variable may not actually exist in the code, I made it
> up.]
> 
> .. and you need to work out how long the queued jobs can run for -- ie:
> 
> 	($QueuedJobs * $WallTime)
> 
> The worst-case response time is the sum of these two values.  
> 
> With a little bit of math:
> 
> [1]	$RunningJobs + $QueuedJobs = $TotalJobs
> 
> [2]	(($RunningJobs * $WallTime) - $UsedTime) +	
> 	(($QueuedJobs * $WallTime) = $wrt
> 
> [1,2]	(($RunningJobs + $QueuedJobs) * $WallTime ) - $UsedTime = $wrt
> 
> =	( $TotalJobs * $WallTime) - $UsedTime
> 
> ... which is what the PBS code above calculates.  If you change
> $TotalJobs to $QueuedJobs in the above calculation then the math just
> breaks.  (As you observed, you'll usually get a negative $wrt.)
> 
> If you removed the $UsedTime and changed $TotalJobs to $QueuedJobs, then
> you would effectively be ignoring the CPU time that has yet to be
> consumed by the jobs currently running on the cluster.  That's probably
> not what you want.
> 
> (Yes, I understand this too much.  I had to understand WTF the above was
> doing when I came to implement my own lcg-info-dynamic-sge!)
> 
> Cheers,
> David