AMD release APP SDK 2.8, CodeXL 1.0 and Bolt

This is old news now that AMD have released APP SDK 2.8, CodeXL 1.0 and Bolt. Bolt is a C++ abstraction of OpenCL which allows you to write OpenCL applications without actually writing OpenCL. I personally haven’t tried it as we are not going to be using it at work but it sounds a good step forward in making GPGPU more accessible to the mainstream. For anyone interested there are a number of blog posts by AMD on how to use Bolt.

OpenCL Cookbook: Multi-device utilisation strategies

A quick note on all the different ways in which one can utilise multiple devices in OpenCL. This overlaps with my previous post on the same subject in the series but is a higher level overview than that previous post.

Here are the different ways one can load balance across multiple devices.

  • Use CPU and GPU devices.
  • Use multiple GPU devices.

For each of the above one can utilise them in the following ways.

  • Single context – Use one context in total across all devices and one command queue per device.
  • Multiple contexts single-host-thread – Use one context and one command queue per device.
  • Multiple contexts multi-host-threaded – Same as multiple contexts above but use one host thread per device to enqueue to the command queue for that device. This can also be in the form of starting one host process instance per device which in essence is the same.

For an elaboration on the latter strategies see my previous post on the subject.

Project Rogue: Conception and specification

Project Rogue in action in Crysis 2
Project Rogue in action in Crysis 2


Project Rogue was conceived out of necessity in September 2012. Constituent components were researched in October 2012 and then subsequently ordered end of October 2012. A week later the project was complete in the sense that it functioned as a whole. It was alive and breathing. One month later, in December 2012, Project Rogue has now completed its extensive accessorisation phase and now I reveal it to you in all its glory.

How was Project Rogue conceived?

Early September 2012 I started working with some insanely powerful desktop workstation hardware – dual xeon 16 core 32 thread watercooled cpus, 8 water cooled gpus, 128GB ram, dual 1200W power supplies and immensely large cases. We were loading up these beasts with heavy computations that were utilising both multiple physical cpus and multiple gpus.

At that time my personal machine at home was a humble 11″ macbook air which although previously had been more than adequate for my needs it had now essentially been made suitably redundant and in a sense outdone. It was clear that I would need something a bit more ambitious to be able to do the kind of work at home that I was doing at work.

Something that would allow me to do uncompromising computations on the cpu and across multi-gpus but within the constraints of a personal budget (which I far exceeded in the end due to my own uncompromising nature). Something that within loose constraints would be uncompromising in its demands for high quality components and power and not settle for what was just good enough – something almost rogue in nature.

What is Project Rogue?

Sadly it’s nothing as grand as the preceding section makes it out to be where I got a little carried away but to me, actually, it is grand for reasons I’ll get into below. Project Rogue is a home computation and gaming rig with modern high quality components within the constraints of a home budget (sadly a characteristically generous one).

There are two things that make Project Rogue highly significant to me which is why it is being made into a series of posts on this blog. Firstly, it is a real world machine born out of a real world need created from scratch in the modern day and I’m sure that there are many that would benefit from an account of the entire process of creating such a rig. I certainly wish there was such a guide for me when I started.

Secondly, and more importantly, this was my first pc build ever which I admit without reservation and given that fact and the calibre of this machine I feel a sense of achievement and would like to catalogue this milestone of mine. I also think that the latter point makes, this account to come, even more valuable for those out there who haven’t done this before in making it that much more accessible and approachable to them.

I have to say, that whilst my assumption was (as always) that I was the only one who hadn’t done anything like this before, that could not have been further from the truth. I was really very surprised to learn that most ex-colleagues and some current colleagues over the years had either had no exposure to hardware to date or had simply become totally disconnected from it in mainstream commodity development.

I’ve been there and I know what it’s like. You’re developing on a virtual machine. You don’t need to know where it runs and you don’t need to care. The illusion of abstraction and portability reassures you that as long as you write your code to be fast it will automatically run faster when put on better hardware but in reality that is not necessarily true. Hardware is never proactively part of the development process and developers are generally unaware of what hardware they are running on in production.

Home computation and gaming rig component list

Here follows the component and accessory list for a home computation and gaming rig. Each component was picked with a particular motivation in mind and I’ll write about those motivations in a separate post. But generally I tried to go for the best, not unreasonably expensive, quality components that were released most recently.

For the experts out there if you are expecting a workstation or server specification build or a high end consumer build such as a multi cpu, xeon or sandybridge build you’ll be disappointed. This is, sadly, a bit simpler and a bit cheaper but at least up to date with ivybridge and the latest 7970 cards. It is a consumer grade build built with two gpu computations and gaming in mind. It is uncompromising in the gpus chosen however. If you’re expecting a full build watercooled solution you’ll also be sorely disappointed. I needed to start with air-cooling but no doubt next up is water.

In terms of cost – the total cost of the following component list comes to £4385 but a few parts having been bought have been replaced and the sales of the older parts are still pending and once they go through the total cost will reduce to £3533 which sounds a little less mindless.

# Component Price Model Vendor Notes
1 Case £143 Corsair Obsidian 650D Amazon, OC Windowed and matte black
2 Motherboard £231 Asus Maximus V Formula/ThunderFX Amazon, OC Multi-gpu PCI-E, dual band wifi
3 PSU £205 Corsair AX1200 Amazon, OC Fully modular and future proof
4 CPU £240 Intel IvyBridge i7-3770K Amazon, OC 4 cores, 8 threads
5 CPU Cooler £80 Corsair H100 Amazon, OC Sealed liquid cooler
6 Memory £200 Corsair 16GB Dominator Platinum Amazon, OC Pure aesthetic beauty
7 GPU 1 £395 Asus Matrix HD7970 Platinum Amazon, OC Top end triple slot AMD radeon card
8 GPU 2 £395 Asus Matrix HD7970 Platinum Amazon, OC Top end triple slot AMD radeon card
9 GPU 3 £380 MSI R7970 Lightning Boost Edition Amazon, OC Top end dual slot AMD radeon card
10 GPU 4 £380 MSI R7970 Lightning Boost Edition Amazon, OC Top end dual slot AMD radeon card
11 Monitor £489 Asus PB278Q Amazon, OC 27″ LED, fully adjustable
12 SSD 1 £171 Corsair Force GS 240GB Amazon, OC 90K IOPS, bright red
13 SSD 2 £171 Corsair Force GS 240GB Amazon, OC 90K IOPS, bright red
14 HDD 1 £66 WD Scorpio Blue 1TB (Spec) (PDF) Amazon, OC Fast 2.5″ 1TB HD
15 HDD 2 £66 WD Scorpio Blue 1TB (Spec) (PDF) Amazon, OC Fast 2.5″ 1TB HD
16 Bluray writer £80 Asus BW-12B1ST Amazon, OC Multi-purpose drive
17 4x SSD Rack £58 Icy Dock 4×2.5″ SSD/HD Rack Amazon, OC 4x drive hot swap rack
18 Fan controller £47 Lamptron FC5V2 Amazon, OC Multi-colour multi-output
19 120mm fans £18 Corsair SP120 Quiet Edition Amazon, OC Radiator fans with red fan rims!
20 120mm fans £10 Corsair AF120 Quiet Edition Amazon, OC Airflow fans with red rims!
21 200mm fan £15 Bitfenix Spectre Pro Amazon, OC Quiet black 200mm fan
22 Speakers £183 Corsair SP2500 Amazon, OC Top end 2.1 speakers
23 Keyboard 1 £11 MS Keyboard 600 Amazon, OC Cheap and nasty
24 Keyboard 2 £70 Logitech G510 Amazon, OC Soft touch with macros
25 Mouse 1 £45 Logitech Performance MX Amazon, OC Cordless
26 Mouse 2 £35 Logitech G500 Amazon, OC Corded
27 USB3 Stick £50 Corsair Survivor Stealth 64GB Amazon, OC Stunning and fast
28 USB3 adapter cable £7 Akasa USB3 adapter cable Amazon, OC Converts usb3 to mb header
29 Thermal paste £10 Artic Silver 5 Amazon, OC Thermal paste and cleaner
30 Cable ties 1 £3 Large velcro cable ties Amazon, OC Multi-coloured and chunky
31 Cable ties 2 £4 Large velcro cable ties Amazon, OC Black and chunky
32 Cable ties 3 £12 Small velcro cable ties Amazon, OC Thin ties bulk pack
33 Power meter £19 Efergy Socket 2.0 Amazon, OC Shows real time watts used
34 Sata cables 1 £5 Akasa 50cm sata3 Amazon, OC Fat sata cable
35 Sata cables 2 £17 4x Akasa super-slim 50cm sata3 Amazon, OC Super slim form factor
36 DVD-R £7 25x Verbatim DVD-R Amazon, OC System restore discs
37 CD/DVD pens £5 Fellowes CD/DVD Pens Amazon, OC No comment
38 External HDD £62 Samsung M3 1TB Amazon, OC Out of case backup

A sneak peek at Project Rogue
Sadly there was only room for two but the sight of four was nice while it lasted!

What’s next in the series?

Project Rogue will become a series starting with a step by step account of its own build in the form of a photo journal and then continuing to document its evolution in real time. I will also focus on important aspects of a computer build that would be relevant to anyone attempting any build. Post Project Rogue there will be another good few builds coming each offering a progression of some kind of previous builds and if I haven’t run out of cash by then and had to shut the site down I’ll document those too! Stay tuned!

Have you donated to Wikipedia?

Do you use wikipedia? Have you ever considered yourself to be privileged to be able to use wikipedia whenever you wanted for whatever you wanted totally free of charge? How many times has it helped you avoid an embarrassing admission of ignorance? How many times has it helped you prepare for a job interview? Considering that – have you ever donated to wikipedia? I just did. And this is the email I received in return.

Dear Dhruba,

Thank you for donating to the Wikimedia Foundation. You are wonderful!

It’s easy to ignore our fundraising banners, and I’m really glad you didn’t. This is how Wikipedia pays its bills — people like you giving us money, so we can keep the site freely available for everyone around the world.

People tell me they donate to Wikipedia because they find it useful, and they trust it because even though it’s not perfect, they know it’s written for them. Wikipedia isn’t meant to advance somebody’s PR agenda or push a particular ideology, or to persuade you to believe something that’s not true. We aim to tell the truth, and we can do that because of you. The fact that you fund the site keeps us independent and able to deliver what you need and want from Wikipedia. Exactly as it should be.

You should know: your donation isn’t just covering your own costs. The average donor is paying for his or her own use of Wikipedia, plus the costs of hundreds of other people. Your donation keeps Wikipedia available for an ambitious kid in Bangalore who’s teaching herself computer programming. A middle-aged homemaker in Vienna who’s just been diagnosed with Parkinson’s disease. A novelist researching 1850s Britain. A 10-year-old in San Salvador who’s just discovered Carl Sagan.

On behalf of those people, and the half-billion other readers of Wikipedia and its sister sites and projects, I thank you for joining us in our effort to make the sum of all human knowledge available for everyone. Your donation makes the world a better place. Thank you.

Most people don’t know Wikipedia’s run by a non-profit. Please consider sharing this e-mail with a few of your friends to encourage them to donate too. And if you’re interested, you should try adding some new information to Wikipedia. If you see a typo or other small mistake, please fix it, and if you find something missing, please add it. There are resources here that can help you get started. Don’t worry about making a mistake: that’s normal when people first start editing and if it happens, other Wikipedians will be happy to fix it for you.

I appreciate your trust in us, and I promise you we’ll use your money well.


Sue Gardner
Executive Director,
Wikimedia Foundation

If you’ve used wikipedia you owe them and all contributors a debt of gratitude. And a donation symbolises a repayment of that debt of gratitude. Donate today. It doesn’t have to be much. £5, £10 – anything that you can afford.

Collapsing two arrays into one in C and C++

A quick tip – if you have two arrays and you want to merge/collapse/concatenate/append/combine (whatever you want to call it) them into one here is one way to do it in C and C++. The code also prints the combined array to check it’s correct.

Note the subtle differences between C and C++. One of the (innumerable!) problems with C++ is that you can write as much C as you want in it and leave the next developer wondering why you were writing C instead of C++ and whether you had specific justifiable reasons to do so in each instance. I personally also consider it bad practice. This is one of the reasons I dislike hybrid languages – they allow you to blend two languages together in arbitrary proportions making the end result unreadable and unmaintainable and just raising more questions than the problems that it solves.


#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main () {

double a[4] = {1,2,3,4};
double b[4] = {5,6,7,8};

double* c = malloc(8 * sizeof(double));

memcpy(c, a, 4 * sizeof(double));
memcpy(c + 4, b, 4 * sizeof(double));

for (int i = 0; i < 8; i++) {
printf("%d %fn", i, c[i]);




#include <iostream>
#include <cstring>
#include <iomanip>

using namespace std;

int main () {

double a[4] = {1,2,3,4};
double b[4] = {5,6,7,8};

double* c = new double[8];

copy(a, a + 4, c);
copy(b, b + 4, c + 4);

for (int i = 0; i < 8; i++) {
cout << i << " " << c[i] << endl;

delete[] c;


Note that in the C++ program:

  • I’m not using includes from C
  • I’m not using memcpy from C
  • I’m not using printf from C
  • I’m not using malloc from C
  • I’m not using sizeof from C
  • I’m not using free from C

8 GPU watercooled computation rig using Power Color Devil 13 HD 7990 cards

Workstation motherboards provide 4 or more PCIE x16 gen 3 slots with a good distribution of dedicated links direct to multiple onboard CPUs. With dual cards such as 7990 which are in fact 2×7970 each one can in theory load up a 4 slot motherboard with 8 gpus in total. Alas, in practice, there can be obstacles booting with 7 or 8 of them with certain motherboads as they tend to run out of PCIE resources after around 6 cards which could be considered to be surprising for a workstation class motherboard. Incidentally, I think it’s worth noting that not only are these the only model of 7990 made but they are practically impossible to get hold of so very rare gems indeed.

Watercooling four dual gpus on a standard workstation motherboard can also be a challenge due to a severe shortage of space between them. Dual slot spacing between PCIE x16 slots is a tight fit as the tubes can take up almost three slots worth of space between cards. In this configuration they are installed on alternate slots so if you had 7 slots in total you’d only install on 1, 3, 5 and 7 leaving 2, 4 and 6 empty. Though 2, 4 and 6 will usually be PCIE x8 slots anyway as opposed to the rest being PCIE x16.

As you can see below these cards have been completely stripped down of their air cooling and heatsink apparatus prior to attaching waterblocks and tubing for coolant to pass through them. The tubing is secured using barb fittings which are stronger than the alternative: compression fittings though they do lack the aesthetic appeal of compression fittings. Compression fittings can come apart under tension and that can create a real mess as I realised the hard way one night.

If not using full card waterblocks (which these aren’t) individual adhesive heatsinks for all the ram chips (known as ram sinks) are required for sufficient cooling. There may be upto 12 of these tiny little ram sinks on each face of a card. I don’t have any photos of that right now but I’ll try and get some. Though, ram sinks, can be flimsy and easily become dislodged and fall off the cards if they are knocked which is why some people prefer full cover blocks. Full cover blocks are more robust but also more expensive.

In terms of power the system is supplied with 2400 watts of power composed of two 1200W power supplies chained by an adapter for the first to kickstart the other on boot. Half the gpus are powered by one and half by the other. This particular machine has 128GB of RAM and dual xeons with a combined total of 32 cores. Update: As rightly pointed out by the commenter below I meant hardware threads not physical cores here.

Note: I do not own the hardware or the photographs but consent has been acquired to publish them here. Also this system is not conceived or assembled by me though I do have the pleasure of loading it with OpenCL benchmarks and computations.

OpenCL Cookbook: Running remote multi-gpu OpenCL computations over SSH on Ubuntu or Debian using AMD Catalyst drivers

Continuing on in the OpenCL cookbook series here I present a post not about code but about environmental setup further diversifying the scope of the cookbook. Here is a no-nonsense guide to running OpenCL programs via ssh remote login into linux. This is intended as a follow up to my previous guide to compiling OpenCL on linux so have a look at that if you haven’t done so already but this account should be fairly self contained nevertheless.

Important: Note that this is not a guide to setting OpenCL on linux in a headless fashion. It requires GUI linux, it requires X and it requires that X be running on screen. Although there are reports of people getting headless setups to work I haven’t yet had time to try these things out so I cannot comment on them.

Install Linux

I went for Ubuntu and Debian for their easy and well known package management. I installed them in adjacent partitions so that I could test my setup on both and compare them easily. Eventually I settled on Debian due to strongly disliking unity and the presence of several known issues with raid on boot in Ubuntu. Regarding desktop environments/window managers I installed an assortment of them because I wanted fully featured ones for development and lightweight ones for benchmarking. I also wanted to test OpenCL in a variety of environments. I installed GNome, KDE, Blackbox, Fluxbox, XFCE and E17 on each distro. It’s good to have options. 🙂 Note that you should NOT install any drivers automatically through the ubuntu/debian package management tools!

Install AMD Catalyst 12.11 beta drivers and AMD APP SDK 2.7

Installing the above is as simple as downloading the linux tarballs, extracting them and running the executable script within each as root. I don’t bother building distro specific packages. Just install the damn things. They work. If you want a bit more elaboration on installing and setting these up look at my previous guide. The reason I’m suggesting the 12.11 beta drivers is because the 12.10 stable driver doesn’t work with X on ubuntu or debian whereas 12.11 beta does. Plus I haven’t noticed any instability with 12.11 beta at all. It seems to work just fine.

Use amdconfig to generate a new Xorg configuration using all adapters

Amdconfig (also aliased as aticonfig) is a powerful command line tool provided by the AMD catalyst driver that you can use for an assortment of tasks such as listing your adapters, querying clocks and temperatures of your gpus, setting overclocks and most importantly for our purposes generating a variety of Xorg configurations with different settings. Here we need to generate an X configuration that will enable all our adapters in Xorg.

sudo amdconfig --initial -f --adapter=all

This will back up your existing xorg.conf in /etc/X11/xorg.conf and create a new one in its place containing device and screen sections for all your gpus. Though if you’ve just installed ubuntu or debian you won’t have an xorg config to begin with anyway.

Reboot to start using the new AMD fglrx driver and your new X configuration

A reboot is required to unload the old open source driver and load fresh the new proprietary amd driver fglrx which cannot be done cleanly by simply using modprobe -r to remove old drivers and modprobe to load new drivers into the kernel and then restarting X. A reboot is recommended and essential. Once you’ve rebooted you’ll also start to use your new X configuration with all adapters enabled. When you see a login manager screen (gdm/xdm/kdm/slim) log into it.

Test your new local OpenCL environment

Start up a terminal. First check that amdconfig sees all your adapters. If you have multiple gpus installed you should see all of them with one of them (typically the first) selected as default.

dhruba@debian:~$ amdconfig --list-adapters
* 0. 05:00.0 AMD Radeon HD 7900 Series
  1. 06:00.0 AMD Radeon HD 7900 Series
  2. 09:00.0 AMD Radeon HD 7900 Series
  3. 0a:00.0 AMD Radeon HD 7900 Series
  4. 85:00.0 AMD Radeon HD 7900 Series
  5. 86:00.0 AMD Radeon HD 7900 Series

* - Default adapter

Next, check that all your devices are being picked up for computation by the OpenCL runtime.As you can see below on my workstation it shows 7 devices – 6 of them being gpus and 1 being the cpu. I’m using 3 7990s each of which are a dual 7970.

dhruba@debian:~$ clinfo | grep 'Number of devices'
Number of devices:				 7

If you see all your devices in the count above your environment should be ready to compile and run OpenCL programs. The next step is get it ready for remote ssh multi-gpu OpenCL computations.

Enable multiple GPUs in the OpenCL runtime

At this point you may find that although amdconfig lists all your adapters the OpenCL runtime only sees one gpu or sees fewer gpus than you have installed. You may also find that some window managers/desktop environments see all devices and others see only one. To enable multiple gpus you may need to do two things.

First you need to disable crossfire. You can do this either from within the catalyst control panel which you can start by running sudo amdcccle or you can use the powerful amdconfig tool to do it by running sudo amdconfig --crossfire=off. See my post about amdconfig for more detail on how to use this amazing tool.

Secondly you may need to pass a hint to the OpenCL runtime to tell it to use the current display for computation as follows.

export COMPUTE=:0

As an alternative to this you can also do the following.


However I’d recommend the first as it is an override flag that does not require any change to the existing DISPLAY variable. Implementing the above two tweaks should enable multi-gpu support in your OpenCL programs. Check either by using clinfo | grep 'Number of devices' or by using a C program as in my previous article.

Install SSH and set up your server for remote computations

Install SSH on ubuntu/debian by running sudo apt-get install openssh-server. This should install the ssh server and start it automatically. Login to your OpenCL server from a remote client and run clinfo again to check number of devices. If this is showing all your gpus then you’re done. However chances are that it won’t yet show all your devices. It will show only your cpu and no gpus at all. The reason for this is that the remote client has not yet been granted access to the X runtime. You can grant access as follows.

dhruba@debian:~$ xhost +
access control disabled, clients can connect from any host

This disables access control altogether. However if you are concerned about security you can be more restrictive and enable it only for specific usernames, hostnames, ip addresses, networks or protocols. See man xhost for details. Basically you append the hostname, username or ip to the plus sign. Once you’ve done the above run clinfo again from your ssh session and now you should see all your gpus and your system is ready to remote OpenCL computations.

Automating setup of remote computation environment

In a true datacentre environment you don’t really want to physically login to X and set environment variables particularly because your server may get rebooted. What you really want is for it to be ready to run OpenCL via remote sessions on a fresh boot without any manual intervention. If you wish to do this there is a guide available on the amd forum for ubuntu specifically which I suppose could be adapted to Debian. I’ve tried this on ubuntu and it does work though it’s a bit hackish. I’ll leave this guide at your discretion.

AMD OpenCL Limitations

Note that this is not a headless setup. In this guide we installed a GUI linux, ran X, logged into X and kept X displayed on screen. All of these are essential. If you either do not run X or run X but switch away from it to one of the other virtual terminals you will not be able to run OpenCL either from the virtual terminals or remotely. If you try to run OpenCL without X running and showing on screen the execution will just hang indefinitely until you start X and display it on screen at which point that hanging computation will continue and complete.

This seems to be an inherent limitation of the AMD driver. AMD say they’re working on separating X from the OpenCL runtime but who knows when this will actually be done. There are quite a few reports of people succeeding at running truly headless OpenCL setups – without any peripherals attached – but I have not had time to research these methods yet so I cannot comment on them.