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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LEARN ABOUT SUNOS

atrm

atrm(1) 							   User Commands							   atrm(1)

NAME

       atrm - remove jobs spooled by at or batch

SYNOPSIS

       atrm [-afi] [ [ job  #] [user...]]

DESCRIPTION

       The atrm utility removes delayed-execution jobs that were created with the at(1) command, but have not yet executed. The list of these jobs
       and associated job numbers can be displayed by using atq(1).

       atrm removes each job-number you specify, and/or all jobs belonging to the user you specify, provided that you own the indicated jobs.

       You can only remove jobs belonging to other users if you have solaris.jobs.admin privileges.

OPTIONS

       The following options are supported:

       -a	All. Removes all unexecuted jobs that were created by the current user. If invoked by the privileged user, the entire  queue  will
		be flushed.

       -f	Force.	All information regarding the  removal of the specified jobs is suppressed.

       -i	Interactive. atrm asks if a job should be removed. If you respond with a y, the job will be removed.

FILES

       /var/spool/cron/atjobs	       spool area for at jobs

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWcsu			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       at(1), atq(1), auths(1), cron(1M), auth_attr(4), attributes(5)

SunOS 5.10							    13 Aug 1999 							   atrm(1)