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Special Forums UNIX and Linux Applications High Performance Computing Memory Barriers for (Ubuntu) Linux (i686) Post 302430480 by gorga on Thursday 17th of June 2010 07:09:41 PM
Old 06-17-2010
Quote:
Originally Posted by Corona688
No significant difference.


Looks like you're right judging by those results. But if I ran it on 4/8/16/32 etc cores, would it still be the case? I have 4-core at work, I'll try it tomoro. Although if LOCK just causes a "re-ordering" of bus-access I suppose theoretically it should impact throughput.

Quote:
How so?
I want to control which queue, and ultimately which pthread runs which task, based on the fact that in the upper application, some tasks communicate very frequently and some never. Also, there is much scope for assigning equal work loads across cores, (think of a n-ary tree structure where the n-paths are of equal length and communication is restricted to nodes of the same path.) I looked at Threading Building Blocks "tasks" at first, but found it too blunt a tool for what I want.

Quote:
I don't see how using a different structure excludes pthreads. You wanted to avoid pthreads since it used atomic ops, and are prepared to use atomic ops instead?
Not really, I originally wanted to use pthreads but they didn't offer the high number of threads and "lightweightness" I needed, (in the order of 10s of 1000s, with many short-lived threads), but user-level threads like GNU threads don't offer multi-core exploitation because the kernel isn't involved. So what I've done, with some inspiration from "protothreads", is provide an abstraction on top of pthreads which provides what I need in the form of lightweight tasks.

I wanted to avoid the pthreads syncrhonisation structures like mutexes because I sought to avoid their overhead and keep it scalable. There are ways to distribute work such that mutexes aren't necessary as long as an ordering of instructions can be guaranteed, hence following your advice, I'll try those atomic instructions from GCC.

thanks!
 

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libmlib_mt(3LIB)						Interface Libraries						  libmlib_mt(3LIB)

NAME
libmlib_mt - multi-threaded mediaLib SYNOPSIS
cc [ flag... ] file... -lmlib_mt -lmlib [ library... ] #include <mlib.h> DESCRIPTION
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. USAGE
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 SYNOPSIS. 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. FILES
/usr/lib/libmlib_mt.so.2 shared object /usr/lib/64/libmlib_mt.so.2 64-bit shared object ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Availability |SUNWmlibt | +-----------------------------+-----------------------------+ |MT-Level |MT-Safe | +-----------------------------+-----------------------------+ SEE ALSO
Intro(3), libmlib(3LIB), attributes(5) mediaLib User's Manual SunOS 5.11 15 Oct 2007 libmlib_mt(3LIB)
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