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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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SHELL-QUOTE(1)						User Contributed Perl Documentation					    SHELL-QUOTE(1)

NAME
shell-quote - quote arguments for safe use, unmodified in a shell command SYNOPSIS
shell-quote [switch]... arg... DESCRIPTION
shell-quote lets you pass arbitrary strings through the shell so that they won't be changed by the shell. This lets you process commands or files with embedded white space or shell globbing characters safely. Here are a few examples. EXAMPLES
ssh preserving args When running a remote command with ssh, ssh doesn't preserve the separate arguments it receives. It just joins them with spaces and passes them to "$SHELL -c". This doesn't work as intended: ssh host touch 'hi there' # fails It creates 2 files, hi and there. Instead, do this: cmd=`shell-quote touch 'hi there'` ssh host "$cmd" This gives you just 1 file, hi there. process find output It's not ordinarily possible to process an arbitrary list of files output by find with a shell script. Anything you put in $IFS to split up the output could legitimately be in a file's name. Here's how you can do it using shell-quote: eval set -- `find -type f -print0 | xargs -0 shell-quote --` debug shell scripts shell-quote is better than echo for debugging shell scripts. debug() { [ -z "$debug" ] || shell-quote "debug:" "$@" } With echo you can't tell the difference between "debug 'foo bar'" and "debug foo bar", but with shell-quote you can. save a command for later shell-quote can be used to build up a shell command to run later. Say you want the user to be able to give you switches for a command you're going to run. If you don't want the switches to be re-evaluated by the shell (which is usually a good idea, else there are things the user can't pass through), you can do something like this: user_switches= while [ $# != 0 ] do case x$1 in x--pass-through) [ $# -gt 1 ] || die "need an argument for $1" user_switches="$user_switches "`shell-quote -- "$2"` shift;; # process other switches esac shift done # later eval "shell-quote some-command $user_switches my args" OPTIONS
--debug Turn debugging on. --help Show the usage message and die. --version Show the version number and exit. AVAILABILITY
The code is licensed under the GNU GPL. Check http://www.argon.org/~roderick/ or CPAN for updated versions. AUTHOR
Roderick Schertler <roderick@argon.org> perl v5.16.3 2010-06-11 SHELL-QUOTE(1)
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