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Special Forums UNIX and Linux Applications High Performance Computing Memory Barriers for (Ubuntu) Linux (i686) Post 302430141 by gorga on Wednesday 16th of June 2010 06:01:30 PM
Old 06-16-2010
Hi Corona, (small world Smilie)

Quote:
Originally Posted by Corona688
You could try using Linux futexes, which handle the nonblocking case completely in userspace, but I'm not sure what that'd do for memory barriers
I hadn't heard of futexes until you mentioned them, but I did some reading and it seems they still use atomic instructions to update shared variables. In that case I could just use one of GCC's built-in atomic operations like "__sync_fetch_ and_ add" or "__sync_bool_compare_and_swap" as described here...

Atomic Builtins - Using the GNU Compiler Collection (GCC)

The thing with these is they use the asm op-code "lock", which issues a hardware lock on the data-bus effectively locking every other process out of memory. Because I'm writing an application that should be scalable for a system with many cores, I'm discouraged by this.

Quote:
Besides, what if you need to move it to MIPS or something?
Could be a possibility, I believe they have made advances into highly parrallel architectures recently, but the project is at a research stage right now so if I can get it to work well on x86 that's good enough for now. I like the sound of this idea though...

Quote:
Could you perhaps reorder it to put prefix, instance, and state in order in memory? You could assemble the data in an MMX or SSE register, then overwrite several structure members in one assembly op.
This could be a good solution, but I'm not sure how to do it. Do you have any examples of similar code as a guide?

Quote:
One thought does occur to me. How large are these structures?
prefix and instance are both uint32_t while state is an enum (guess that means its a uint32_t also?).
 

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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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