Memory Barriers for (Ubuntu) Linux (i686) Post: 302431048

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Special Forums UNIX and Linux Applications High Performance Computing Memory Barriers for (Ubuntu) Linux (i686) Post 302431048 by Corona688 on Sunday 20th of June 2010 09:14:36 PM

06-20-2010

Registered User

Quote:

Originally Posted by gorga

Let me put it this way, I have a list of jobs to do, as I progress through the list I find some jobs aren't ready. I can either block/sleep etc and wait for the job to become ready, or I can move onto the next task and execute that one instead.

...and when you don't assume best-case, you could be going through the next few thousand not-ready tasks. Meanwhile every idle worker's doing the same thing. I begin to understand why you're concerned about contention for memory.

Quote:

If I build my system with locks, I'll adhere to the first approach, whereas what I'm trying to achieve (aided by atomic flags and memory barriers) is the second.

But because it doesn't block, you'll be wasting time scanning the list anyway, time that could have been spent doing actual work. And since your system's as busy idle as it is when actually busy you'll have a difficult time guessing how much. If I read you correctly, the jobs are all tiny. How tiny? How much more work is it to do a job than to scan the list? (And don't assume it could never, ever become mostly empty, that's the goal, not the proof.) If they're even in the same ballpark, you're going to be wasting a worrying proportion of CPU time scanning your list.

Anyway, the queue needn't block like you're describing. Put jobs in the queue when they become ready, don't just stick them there in advance, that way threads won't block when picking up jobs unless you're actually out of jobs -- in which case you want them to block. If the queue's big enough and jobs can be added fast enough, things can run smoothly. You can also do other things to streamline the queue -- hand out jobs 16 at a time instead of one at a time, switch between multiple queues, etc.

Last edited by Corona688; 06-20-2010 at 10:33 PM..

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condor_router_q

condor_router_q(1)					      General Commands Manual						condor_router_q(1)

Name
       condor_router_q Display - information about routed jobs in the queue

Synopsis
       condor_router_q [-S] [-R] [-I] [-H] [-route name] [-idle] [-held] [-constraint X] [condor_q options]

Description
       condor_router_q displays information about jobs managed by the condor_job_routerthat are in the Condor job queue. The functionality of this
       tool is that of condor_q, with additional options specialized for routed jobs. Therefore, any of the options for condor_qmay also  be  used
       with condor_router_q .

Options
       -S

	  Summarize the state of the jobs on each route.

       -R

	  Summarize the running jobs on each route.

       -I

	  Summarize the idle jobs on each route.

       -H

	  Summarize the held jobs on each route.

       -route name

	  Display only the jobs on the route identified by name.

       -idle

	  Display only the idle jobs.

       -held

	  Display only the held jobs.

       -constraint X

	  Display only the jobs matching constraint X.

Exit Status
       condor_router_q will exit with a status of 0 (zero) upon success, and non-zero otherwise.

Author
       Condor Team, University of Wisconsin-Madison

Copyright
       Copyright  (C)  1990-2012  Condor  Team,  Computer  Sciences Department, University of Wisconsin-Madison, Madison, WI. All Rights Reserved.
       Licensed under the Apache License, Version 2.0.

       See the Condor Version 7.8.2 Manualor http://www.condorproject.org/licensefor additional notices. condor-admin@cs.wisc.edu

								  September 2012						condor_router_q(1)