interesting tools and compilers (for P4, Athlon, Opteron)

[Dresdenboy]

Hello,

since I run into interesting software pieces and sites, I'll give an overview, what could be useful for prime95 development:

an low overhead profiler for linux, using performance counters of Intel/AMD, can go down to instruction level:
http://oprofile.sourceforge.net/

AMD CodeAnalyst 2.1 beta (like VTune, but free, has Pipeline simulator for various AMD CPUs, performance counter and timer based profiling)
http://www.amd.com/us-en/Processors/...2_3604,00.html
(I used 1.2 before for optimizing my SSE/MMX game of life code)

Portland Group compiler 5.0 beta with support for Opterons 16 SSE2 and int registers, which is surely better optimizing for the schedulers and latencies than Intel C++. You can download a free version - with Opteron binaries - for Win and Linux here:
http://www.pgroup.com/AMD64.htm

GCC 3.3 has better x86-64 support. A complete package (MingW versions) can be found here:
http://www.thisiscool.com/gcc33_mingw.htm

Surely the compilers won't be useful for the handcrafted assembler, but one could look what code they produce for key parts of the algorithm.

More interesting would be a pipeline analysis of the hotspots. I don't know if such a thing is possible for Intel based systems now, but simulating for Athlon/Opteron could give some clues.

EDIT: CodeAnalyst 2.1 doesn't have the nice graphical pipeline analyzer which was present in version 1.2. Now it's a command line tool. Its still very useful (because of SSE2 and x86-64 support). To get a clue, what it looks like in 1.2 (you can get version 1.2 and some info by searching google for "AMD Codeanalyst" and opening the cached page) here's a screenshot. The colored boxes have meanings like "dispatch" (yellow), "execute" (green), "retiring" (grey), some stall (red border) and so on. Moving mouse pointer over a box gives detailed info about what's happening with this instruction during that particular cycle.
http://www.informatik.uni-rostock.de...odeAnalyst.jpg

[Dresdenboy]

screenshot and more info added (I write this because there is no notification about my edit)

[Prime95]

Dresdenboy, your ID makes me think you work for AMD! In which case I'm almost ashamed to ask this question: "Does CodeAnalyst work on Intel CPUs - especially the pipeline analyzer?" I know it won't tell me anything about Intel's pipelines but it would be cool if it would help an Intel owner optimize his code for an AMD CPU.

[gbvalor]

Hello,

Nice review!. I'm still waiting for something like CodeAnalyst ... but for linux :-(

Originally Posted by Dresdenboy

GCC 3.3 has better x86-64 support. A complete package (MingW versions) can be found here:
http://www.thisiscool.com/gcc33_mingw.htm

I've had bad experiences with GCC 3.3 and SSE2 support. It is indeed bugy a lot managing SSE2 code. Actually I have to work with unstable CVS GCC 3.4 snapshots. It works OK for Glucas with no problems for pentium4 and Opteron support.

Guillermo.

[Dresdenboy]

Originally Posted by Prime95

Dresdenboy, your ID makes me think you work for AMD! In which case I'm almost ashamed to ask this question: "Does CodeAnalyst work on Intel CPUs - especially the pipeline analyzer?" I know it won't tell me anything about Intel's pipelines but it would be cool if it would help an Intel owner optimize his code for an AMD CPU.

That's even not farfetched ;) But not me works there. It's one of my friends who's a fab worker in Dresden. I'm just someone who likes to optimize code since 6502, 68k, 386 times. But since this work is often already being done for Intel CPUs these days someone needs to do (or help to do) it for AMD.

CodeAnalyst works on all x86 CPUs - except that event based profiling isn't possible. CA checks for availability for certain events. Here at work (not AMD) there are some PIII and P4 systems. On PIII the CodeAnalyst 1.2 pipeline analyzer works perfectly. You can select a CPU (K6-2, Athlon, Duron, Athlon XP/MP) and select the multiplier for simulation.

That was a nice way to study SSE behaviour (and to find out, that MMX is faster for AND, NOR etc.). I saw that the scheduler often was just full of ops because there were no integer ops in about 30 SSE instructions and sometimes it had to wait for Load/Store unit because of reusing of a stored value.

In CodeAnalyst 2.1b also Athlon 64/Opteron code can be simulated. Maybe I'll write a gui some day if it's not planned at AMD.

Opteron also has better options for doing SSE2 than Athlon XP has for SSE because many of the important ops are now directpath or double (mOP) decoded and don't fill up the issue ports like before which would allow us to start some 64bit mul or so.

DDB

[Dresdenboy]

Some interesting fact about the Intel compiler:
http://www.aceshardware.com/forum?read=95033881 quotes the Inquirer that people found out, that SSE2 code compiled on Xeon runs much faster on Opteron than when it's compiled on Opteron itself (using the same options and target).

A comment (http://www.aceshardware.com/forum?read=95033983):

If you compile on Opteron platform, the compiler detects the chip and produces poor performing code, so you have to compile on a P4.

There is an IFDEF that basically says "If AMD chip detected, disable optimizations".

The opportunity to insert that function is why Intel has been spending a ton of money buying out any compiler producers it can.

Well, for me at home (Athlon XP) the created code is really fast. But I'll make a test and will also compile it on P4 for trying at home.

DDB

[Xyzzy]

Originally Posted by gbvalor

Nice review!. I'm still waiting for something like CodeAnalyst ... but for linux :-(

Is VTune the same thing?

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[gbvalor]

Hello,

Originally Posted by Xyzzy

Is VTune the same thing?

Is almost the same thing. The free evaluation is only valid for 7 days. When one (as me no too much skilled) has learnt the use of Vtune the license has expired :-( . OTOH, I can't spend 699$ in a Vtune License. This is why I'm anxious to see something free for non commercial pruposes (as the Intel compilers).

AMD people!, Linux has been the OS with better and faster support for your new processors. It's time to offer to the developers performance tuners and compilers for your hardware. ;) isn't it?

Guillermo.

[Dresdenboy]

Originally Posted by gbvalor

Hello,
Nice review!. I'm still waiting for something like CodeAnalyst ... but for linux :-(

Have a look at the also mentioned Oprofile for Linux, which has counter based profiling down to instruction level both for Intel/AMD.

If there is some pipeline analysis necessary one could put some hotspot functions into a small cygwin/mingw app using the same compiler (GCC/ICC) and analyse it under windows.

There is even no program database or debug info needed for CodeAnalyst 2.1 but it's good to know the start adress for a trace. I used CodeAnalysts graphical interface to find a suitable start adress when going down to disassembly level - that's possible without sourcecode/program database - but then you don't see associated sourcecode lines or function names.

While I profiled my game of life here, I also profiled Prime95, Win2k kernel and other running code where you also can have a look at in disassembled view.

Pipeline analysis of this game of life also shows, that it runs ~40% faster on Opteron compared clock per clock to XP.

Regards,
DDB

[Dresdenboy]

A short info about CodeAnalyst 2.1b:

As I found out the command line tools for pipeline analyzing produce a binary file, which could be used for creating a graphical visualisation like in CodeAnalyst 1.2. Currently it's only used to produce simulation reports.

DDB

[gbvalor]

Originally Posted by Dresdenboy

Have a look at the also mentioned Oprofile for Linux, which has counter based profiling down to instruction level both for Intel/AMD.

Oprofile looks very interesting but I need to compile a new kernel. So I must do things carefully.

Thanks, Dresdenboy. Your suggestions have been useful to me.

If you like, you can get and test Glucas code at:

http://sourceforge.net/projects/glucas

There is still no release for SSE2 code, this is currently partially implemented and you can download it from CVS repository.

Guillermo.