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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
Old 06-20-2010
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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libmlib_mt(3LIB)														  libmlib_mt(3LIB)

NAME
libmlib_mt - multi-threaded mediaLib SYNOPSIS
cc [ flag... ] file... -lmlib_mt -lmlib [ library... ] #include <mlib.h> Interfaces in this library provide functions for multimedia processing. Multi-threaded (MT) mediaLib is a software layer developed on top of mediaLib using OpenMP. When it is used with a large data set on a multi-processor system, MT mediaLib will partition data into subsets and process the subsets in parallel, thus greatly improving performance of applications that use mediaLib. INTERFACES
The shared object libmlib_mt.so.2 provides the same public interfaces as those defined in libmlib(3lib). See intro(3) for additional infor- mation on shared object interfaces. There are two ways to use MT mediaLib. 1. Pre-load a multi-threaded mediaLib library during runtime by setting the LD_PRELOAD environment variable as follows before starting your application, in Bourne/Korn shell: LD_PRELOAD=libmlib_mt.so export LD_PRELOAD or in C shell: setenv LD_PRELOAD libmlib_mt.so In this way, you can take advantage of MT mediaLib without rebuilding your application. 2. Link your application with a multi-threaded mediaLib library directly as shown under . In this way, an MT mediaLib library is always used whenever your application is started. The parallelization of MT mediaLib is controlled, in part, by the PARALLEL environment variable. You can change its setting to adjust the degree of parallelization before starting your application, in Bourne/Korn shell: PARALLEL=n export PARALLEL or in C shell: setenv PARALLEL n where n is a positive integer for number of threads. Note that other factors also affect the degree of parallelization in MT mediaLib. /usr/lib/libmlib_mt.so.2 shared object /usr/lib/64/libmlib_mt.so.2 64-bit shared object See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Availability |SUNWmlibt | +-----------------------------+-----------------------------+ |MT-Level |MT-Safe | +-----------------------------+-----------------------------+ Intro(3), libmlib(3lib), attributes(5) 30 Sep 2005 libmlib_mt(3LIB)
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