Getting glGetString To Return Something Useful

Here's a small-but-useful factoid.

In OpenGL, glGetString() is the API to query the configuration of the system your code is running on, like the OpenGL version, or which OpenGL extensions are available.

However, if you call glGetString() before you have a current GL connection, no matter which configuration string you're querying, it will just return a NULL (nil) pointer.

If you're working in GLX, the solution is to call glXMakeCurrent() before calling glGetString(). That will open a current GL connection and you'll start getting strings back.

Unfortunately, most GLX tutorials and sample code either assume you know this, or use a utility library like GLUT that solves the problem for you without telling you how. After reading the man pages, this solution seems pretty obvious in retrospect. But as far as I can tell, it's only clearly spelled out in one place on the Net - until now. (That page also tells what to do on Windows.)

Linux Builds Part II: The Acceleration Incantation

Ubuntu offers a system monitor that can show graphs of how system resources are being used. It's very interesting to turn on all the graphs on and build a large project without fiddling with the build. You'll see some interesting things.

First, the CPU usage will jump up and down, and so will the disk activity - but you'll rarely see them both high at the same time. That's because the compiler typically operates in three phases on a source file:

1. It reads the source file and all the headers. This is disk-intensive but not CPU-intensive.
2. Then it does all the usual compiling stuff like lexical analysis and parsing and code generation and optimizing. This makes heavy use of the CPU and RAM, but doesn't hit the hard disk much.
3. Then it writes the object file out to disk. Again, the disk is very busy, and the CPU just waits around.

So at any one time, the compiler is making good use of the CPU or the disk, but not both. If you could keep them both busy, things would go faster.

The answer to this is parallel builds. Common build tools like make and jam offer command line options to compile multiple files in parallel, using separate compiler instances in separate processes. That way, if one compiler process is waiting for the disk, the Linux kernel will give the CPU to another compiler process that's waiting for the CPU. Even on a single-CPU, single-core computer, a parallel build will make better use of the system and speed things up.

Second, if you're running on a multi-CPU or multi-core system and not doing much else, even at its peak, CPU usage won't peg out at the top of the panel. That's because builds are typically sequential, so they only use one core in one CPU, and any other compute power you have is sitting idle. If you could make use of those other CPUs/cores, things would go faster. And again, the answer is parallel builds.

Fortunately, the major C/C++ build systems support parallel builds, including GNU make, jam, and SCons. In particular, GNU make and jam both offer the "-j X" parameter, where X is the number of parallel jobs to compile at the same time.
The graph above shows what I would generally expect the results of parallel builds to be on a particular hardware configuration, going from left to right.

• When running with one compile at a time, sequentially, system resources are poorly utilized, so a build takes a long time.
• As the number of compiles running in parallel increases, the wall time for the build drops, until you hit a minimum. This level of parallelization provides the balanced utilization of CPU, disk, and memory we're looking for. We'll call this number of parallel compiles N.
• As the number of compiles passes N, the compile processes will increasingly contend for system resources and become blocked, so the build time will rise a bit.
• Then as the number of parallel compiles continues to rise, more and more of the compile processes will be blocked at any time, but roughly N of them will still be operating efficiently. So the build time will flatten out, and asymptotically approach some limit.

Anticipating further posts, that is what you actually see, except the rise after the minimum is tiny, often to the point where the times in the flat tail are only a tiny bit higher than the minimum time.

A Brief Aside On Significance

In any physical system, there's always some variation in measurements, and the same is true of computer benchmarks. So an important question in this kind of experimentation is: when you see a difference, is it meaningful or just noise?

To answer that, I ran parallelized benchmarks on Valentine (a two-core Sony laptop) and Godzilla (an eight-core Mac Pro). In each case, the Linux kernel was built twenty times with the same settings. Here are the results:

• Valentine, cached build, j=3. Average 335.91 seconds, standard deviation (sigma) 2.15, or 0.64% of the average.
• Valentine, non-cached build, j=3. Average 340.09 seconds, standard deviation 4.22, or 1.24% of the average.
• Godzilla, non-cached build, j=12. Average 67.82 seconds, standard deviation 0.54, or 0.79% of the average.

Generally speaking, a difference of one sigma or less is probably not significant, while a difference of two sigma or more is probably significant. So I'll generally use the rule of thumb, based on the above, that differences between individual values of 2% or less are probably not significant and may easily be due to experimental error (noise).

Linux Build Optimization I: The Need for Speed

gcc may be many things, but it most certainly is slow. Anybody who's worked with a really fast C/C++ compiler - like the late, lamented Metrowerks Codewarrior for MacOS and Windows - will be happy to tell you that.

But build speed matters a lot! As Joel Spolsky points out:

If your compilation process takes more than a few seconds, getting the latest and greatest computer is going to save you time. If compiling takes even 15 seconds, programmers will get bored while the compiler runs and switch over to reading The Onion, which will suck them in and kill hours of productivity.

I currently work with a team on a Linux-based system involving about twenty million lines of C/C++. Building everything using the default settings on our normal development hardware takes hours. So if someone changes a file down in the bowels of some low-level component half the system relies on, here's how we spend our time:

What can we do?

Here are some options for speeding up the build cycle. I think they would all be great if everybody could do them, but only one of them is universally applicable:

Change to a faster compiler that will do the job

That would be lovely if there were one - but unfortunately, the easily-available option I know of for replacing gcc is the combination of LLVM and clang. I have high hopes for that compiler system someday, but at present, real-world benchmarks don't indicate it's hugely faster at compiling than gcc, and clang doesn't support critical C++ features many programmers need.

Throw money at hardware

This would also be lovely if everyone were in a position to do that. But if you just don't have much spare money, this is a non-starter. And even if you do have a fair bit of change to spend on hardware, what I plan to discuss will still help you improve your use of it.

Be clever

Now we get to the meat of these posts: taking your existing gcc compiler, and your existing hardware, and tweaking things so that the build cycle is quicker. The best case would be without spending a dime, and the worst case would involve spending very little money.

The Ground Rules

These posts will largely consist of a series of experiments. Each experiment will involve applying a technique that might accelerate builds, benchmarking it, and analyzing the results.

Unless otherwise specified, the tests will involve:

• Building the Linux 2.6.30.3 kernel using the default x86 configuration. (If you look at the various components used for the distcc benchmarks, the Linux kernel seems like a pretty representative large set of code.)
  
• Running under Ubuntu 9.04 using gcc version 4.3.3.
• The benchmark is the first thing done after rebooting the computer, with nothing but a couple of terminal windows running.
• The benchmark script, by default, avoids unrealistically fast builds due to disk caching from previous passes. (It does this by unpackaging the kernel tarball on every build pass.) It also has options to support disk caching, and allow adjustment of build options such as parallelization.

The results are all based on "wall time" - what you'd see on a clock on the wall - because I mainly care about not wasting my time waiting for builds.

Major Factors That Determine Build Speed

When you're doing a build, the main things that happen are:

• The CPU calculates things and makes decisions
• The hard drive reads and writes files
• Memory-based data is read from and written to RAM.

The fastest build you could do on a particular set of hardware would strike a balance among the CPU, hard drive, and RAM, so that all of them are constantly busy, with none of them ever waiting any of the others.

Realistically, you will never achieve that 100% utilization on all three components. Even if you adjusted the system so that file foo.c would compile at 100% utilization on all three, if file bar.c used more or larger header files, compiling it might not achieve 100% CPU utilization because the system would spend more time reading header files from the disk, and the CPU would have to wait for that. Also, settings that are optimal for the compiler might not be optimal for the linker. So all we can aim at is an overall good build time.

There are other resources one can apply to compiles which I also plan to address - in particular, underutilized CPU horsepower out on the network via distcc.

So on to the next post... and I would love to get feedback and suggestions!

Installing FogBugz on Ubuntu 9.04

Joel Spolsky is a notable netizen in the technology industry for a variety of reasons, including his blog, Joel on Software, his articles for Inc. magazine, his speeches at many industry conferences, and co-founding the Stack Overflow programmers' website.

Joel's day job is as CEO of Fog Creek Software, and Fog Creek's flagship product is FogBugz, an inexpensive web-based issue tracking system with some other nice features like an integrated wiki.

When my wife and I switched from Mac OS 9 to Mac OS X for day-to-day productivity work, we'd been using Seapine's TestTrack for bug tracking, but it became less and less viable for us. So she did a search for alternatives, and liked FogBugz the best. The commercial bug tracking systems were pretty expensive, and there weren't any open-source equivalents with good documentation at the time.

FogBugz is still quite reasonable for a small team that doesn't have IT staff: it's pretty cheap, and pretty good, and pretty functional, and pretty bug-free, and doesn't take a lot of administration or maintenance. Some of the open-source alternatives like Trac have probably caught up with it on features and ease of installation and administration. But FogBugz costs only $36.50 per programmer per year for a maintenance contract, so it' s not worth it to us to switch.

However, in my opinion, FogBugz has one big flaw. While it runs on Windows, Mac OS X, Linux, and Unix servers, the FogBugz documentation and support is heavily Windows-oriented. If you want to install on a non-Windows platform, Fog Creek's instructions are decidedly not turnkey and not updated even yearly. Their tech support people are nice, and happy to transfer licenses or point you to hard-to-find documentation URLs, but if you're having an unusual problem on a non-Windows platform that their documentation doesn't cover, they are of limited help.

Anyway, I decided to upgrade our FogBugz server from an older version of Ubuntu to 9.04 (Jaunty Jackalope), and did so by wiping the hard drive and re-installing everything, including FogBugz. So here are the general steps, after you've installed Ubuntu. This also is not exactly turnkey - you should be a reasonably knowledgeable Ubuntu user and know when to sudo things, for instance - but it should help keep you from running into roadblocks.

Review a few URLs

You should at least skim these, and may want to print them out.

Here are some Fog Creek pages, but don't take them for gospel truth. I'm writing this post to correct and expand upon them: Getting Your Unix Server Ready For FogBugz and Unix System Requirements.

You should also look at ApacheMySQLPHP on the Ubuntu site, which has some slightly dated background on other components you'll need to install and configure.

Install a LAMP stack

The FogBugz documentation's list of packages to install is very dated and incomplete. You don't need to install mono because it's included with Ubuntu 9.04 desktop. But you need to install a lot of other packages so that the Apache, MySQL, and PHP parts of a LAMP stack will work correctly with FogBugz. Here's what I eventually wound up installing via Synaptic:

• apache2
  
• php5
  
• php5-cli
  
• php5-imap
  
• php5-dev
  
• mysql-server
  
• mysql-client
  
• curl
  
• php5-mysql
  
• php-pear
  
• mono-gmcs
  
• mono-devel
  
• php5-curl
  

When you install mysql, you'll have to give it an administrator account name and password. Remember these! You'll need them later.

And then these two are just handy:

• mysql-query-browser
  
• mysql-admin
  

Configure Networking, Apache, and PHP

If your server has a static IP address, edit /etc/hosts, and make sure your local and fully-qualified machine names (both foo and foo.example.com) are associated with that IP address.

Edit /etc/apache2/httpd.conf and add a server name line:

ServerName foo.example.com

Make sure all the PHP modules are enabled, and then restart the Apache web server:

sudo a2enmod php5

sudo /etc/init.d/apache2 restart

Set up a test page for your PHP extensions: edit /var/www/test.php and fill it with the PHP test info from here. Then open http://localhost/test.php in Firefox and make sure the XML, imap, mysql, and iconv lines all have a 1 at the end.

Install eAccelerator

eAccelerator is a caching system for PHP that FogBugz highly recommends. I do, too - when you're working with the FogBugz database from a client machine over a network, if you don't have eAccelerator installed, you'll be going on a lot of coffee breaks.

Unfortunately, Ubuntu doesn't supply an eAccelerator package, so you have to build it from sources. The official page on how to do this is here, but I didn't find it very helpful on Ubuntu. This page is a lot more accurate and detailed for Ubuntu installation.

Configure MySQL

First, you'll need to get a MySQL prompt. You did write down your administrator name and password above, right?

mysql -u your_administrator_name  -p

and enter the password when prompted.

Then, you'll need to follow the instructions here.

I populated my FogBugz database by a simple directory copy of an old version, so I didn't run into this today. But from an earlier installation, I knew that FogBugz is not compatible with the most recent MySQL password scheme. That means if you're doing an initial installation or you're populating the database via export/import, you'll have to follow some further instructions to tell MySQL to use an older password scheme.

Install FogBugz

Download and unpackage the FogBugz tarball, and follow the Unix Setup Steps instructions. Unlike the instructions, I ran install.sh as superuser. When you run the install, it will ask if you want to install various Pear files; just type "y" for all of them.

Eventually, you'll get to a web-based FogBugz configuration screen. You still do remember that MySQL administrator account information, right? Here's what I used:

Server: localhost

...

Database name: fogbugz

FogBugz user account: fogbugz

Then the web screen will ask you for your Fog Creek order number and email address, and try to validate it with the Fog Creek license server. If you're doing a new installation, after this, you should be up and running.

I was transferring the database and license from a previous installation. That confused the Fog Creek license server and it wanted me to call in to get my installation count incremented. However, I had done a straight backup of /var/lib/mysql/fogbugz on the older installation, so I:

1. Closed the web browser page that was telling me to call Fog Creek.
2. Shut down mysql
3. Did a cp -pr from the backup into my new installation
4. Did a chown/chgrp of the copied files to mysql, and
   
5. Restarted mysql

And at that point, FogBugz was back in operation.

It all took a few hours, and would certainly have been a lot quicker if I'd had this post!

Update (16 July 2009)

David Llopis remarked in the comments: I think if you install "apache2", Ubuntu defaults to installing "apache2-mpm-worker" rather than the "apache2-mpm-prefork" that you should use.

You do need prefork for PHP to run correctly, and David is correct if you do something like just go into Synaptic and select the "apache2" package and hit the "Apply" button.. However, if you don't hit the "Apply" button right away, and select the "php5" package, that will deselect the worker package and select the prefork package. Anyway, you should definitely double-check that you're installing prefork, particularly if you're installing in a different Ubuntu version than 9.04.

Also, Chris Lamb posted instructions on installing FogBugz into Debian Lenny; they contain a few configuration tweaks that might be worth a look.

Curing Ubuntu's Black Screen of Death on a Mac Pro

My wife recently gave me her very recent Mac Pro, and I wanted to set it up for triple-boot Leopard, Snow Leopard, and Ubuntu 8.10 (Intrepid Ibex). The Mac OS X installs were, of course, trivial - but much to my surprise, Ubuntu wasn't.

I'd recently used the general approach from the Ubuntu wiki to set up an old Intel iMac with dual-boot Leopard/Intrepid, and everything went like clockwork:

1. Boot from the Leopard install DVD
2. Early in the OS X install process, use Disk Utility to create a small HFS Plus partition and a big partition I would later snuff for use by Ubuntu, then install Leopard.
3. Install rEFIt.
4. Use a GParted LiveCD to turn the partition from step 2 into free space.
5. Install Ubuntu Intrepid from a LiveCD.

Then I went to do the same thing for the Mac Pro, but when the LiveCD went into graphics mode, the screen went black.

That was odd, since lots of people have reported successfully installing various Ubuntu versions on Mac Pros.

Now, black screens for Ubuntu are not unusual; they generally indicate some kind of driver or X configuration mismatch. I routinely run into them when doing kernel updates on one of my boxen, and the usual search engines offer lots of hits for solutions. But none of the usual techniques worked on this particular Mac Pro.

To cut to the chase, here's the solution. Starting after Step 3 above...

1. From the Mac System Profiler, determine the manufacturer and details of your video card. (Mine was an ATI Radeon HD 2600 with 256 MB RAM.)
2. Start the installation from the Ubuntu Alternate CD, which uses an old DOS-style text mode for its user interface. (If you use the LiveCD or LiveDVD, it will try to go into graphics mode and you're toast.)
3. Zap that big partition you made as part of the installation process. You may also have to manually specify the size of your swap space. You can look up details on how to do this using the usual search engines.
4. When you reboot at the end of your Ubuntu install, you'll get the black screen. Press command-control-F1 to switch to a command prompt. (The meta-keys may be different if you picked a non-Macintosh keyboard during install.)
5. Use sudo apt-get to update everything, and reboot.
6. When the screen goes black, use the key combo again to get a command prompt. Use sudo apt-get to install envyng-gtk. Then do sudo envyng -t.
7. Pick the manufacturer of your video card from the envyng list, then reboot.

At that point, I was successfully booting into the Ubuntu GUI.

Triple-Boot Sony Vaio VGN-AR Notebook - Part II: How I Did It

I finally got my Sony Vaio VGN-AR290G laptop to triple-boot XP, Vista, and Ubuntu. Here's the general gist of how I did it.

This is not a detailed how-to - it's pretty general, and only includes the major steps but not the details. So if you decide to do this, you should read it fully first, and then look up any specific steps you're not sure about. You also need to be sure to read this article first.

1. Make sure the hard drivers are not coupled as RAID. The instructions for this are in my previous post.
2. Put a recent GParted boot CD in the CD-ROM drive and reboot. (I used version 0.3.9-4.) Use GParted to delete all partitions from both drives. Don't create any new ones. Exit GParted.
   
3. On an existing XP installation, go to the AR290G support page and download the one file under the RAID heading - the file description is "Original - Intel® RAID Driver". You don't need anything else from there right now.
   
4. Make an empty directory somewhere on the XP installation machine. Run the program you downloaded in step 4. It will want to install files onto a floppy, but change it to install the files into the directory you made. Those files are the driver files you'll slipstream.
   
5. On the same existing XP installation, go to the nLite home page and download the nLite slipstreaming utility.Get an original Windows XP SP2 installation disk (I made mine from the MSDN Professional DVD). Use nLite per the instructions from the site I told you to read above to create a slipstreamed XP installer ISO image.
   
6. Burn the ISO image onto a blank CD-ROM. This is your slipstreamed XP installer CD. I used a MacBook to do this; the Mac OS Disk Utility works great for this and comes for free with Mac OS. There are other utilities to do this on Windows (e.g. Nero) and Linux (e.g. Brasero) that will work fine as long as you have a compatible CD burner.
   
7. Put the slipstreamed XP installer CD into the Vaio and reboot. It will eventually tell you there are no installable disk partitions, and give you the choice of formatting one. Format a partition on the first drive that only uses part of the drive, and install there. (My two drives are each about 93 GB, so I made this partition 40 GB). Finish the XP install, and reboot. Verify you can boot from your XP installation.
   
8. Put a Vista installer CD or DVD into the Vaio and reboot it. (I used a Vista Ultimate DVD that came with an MSDN Professional subscription.) Tell it to install into the unformatted space on the first drive. (This is the leftover space on the first drive from the last step.) Finish the installation, and verify the Vista bootloader appears and lets you boot either from Vista or an "earlier" version of Windows (your XP installation). Verify you can boot into each Windows version.
   
9. Put a Ubuntu 8.10 Alternate Install CD into the Vaio and reboot it. Tell it to install into the largest unformatted space, which will be the entire second drive. Finish the installation. In one of the last screens, confirm that grub should let you boot into either Ubuntu or the Vista bootloader.
   
10. After removing the Ubuntu CD, verify you can boot into Ubuntu, Windows XP via the Vista bootloader, and Windows Vista via the Vista bootloader.
11. Now you're triple-booting, but there's one more important step. On a computer other than the Vaio (the XP system from step 3 will work fine), go back to the AR290G support page and download installers for video and networking drivers, and any other drivers or programs you think you'll need. Copy them onto a USB flash drive, then boot into XP on your Vaio, attach the USB flash drive, and install the drivers and programs you downloaded.
    

You're done!

Questions and Answers

Q: Why did you decouple the RAID?

A: I had tried this with RAID enabled, and was able to get either XP or Ubuntu working, but not both at the same time. Also, my main interest in this machine is doing compiles. I ran some benchmarks, and saw absolutely zero benefit to using RAID.

Q: What? Using RAID provided no benefit?

A: Yes. I set the system up as RAID 0, installed Ubuntu, and compiled gcc 4.3.2. Then I decoupled the drives, re-installed Ubuntu, and compiled gcc 4.3.2. And I got the following results:

• Extract (tar xf) the gcc tarball: RAID0 2.5s, No RAID 10s
  
• ./configure: RAID0 5s, No RAID 6s
  
• make (sequential compile): RAID0 1h 26m, No RAID 1h 26m
  
• make -j 8 (parallel compile): RAID0 13m 22s, No RAID 12m 50s
  

Q: That's weird. Why do you think RAID doesn't accelerate compiles?

A: Because gcc is not disk-bound, it's CPU-bound. On top of that, I believe the RAID in the Vaio is "fake RAID", which uses the CPU to implement some of the RAID capabilities. So when you do parallel compiles and really beat up the CPU, the extra CPU overhead to implement the RAID actually slows down the compile. (It's possible other compilers, such as Visual Studio, might benefit from a RAID 0 configuration, but that's just a guess.)

Q: Why did you use GParted and Ubuntu Alternate Install?

A: I had them handy. I suspect that I could have used the Ubuntu LiveCD. Then in step 3 I would have booted from the LiveCD and used the Partition Editor, and in step 12 I would have installed from the LiveCD. But I don't know for sure this will work.

Q: Why did you install all those drivers into XP at step 13? Why not slipstream them in step 8?

A: I couldn't figure out an easy way to slipstream them, and this way works fine.

Triple-Boot Sony Vaio VGN-AR Notebook - Part I: RAID Uncoupling

I needed a portable development machine that would let me triple-boot XP, Vista, and Ubuntu.

So far, not a problem - but here's the kicker: it also needs a PCMCIA Type II (CardBus) slot. I occasionally code for a dated interface which, for laptops, is only available in PCMCIA. Unfortunately, PCMCIA has almost entirely been replaced by ExpressCard. As far as I can tell, in late 2008 you can get it on a few expensive Dells, a few of Acer's low-end Extensas - and Sony's Vaio VGN-AR series.

These Vaios had a lot of other things I liked, including a nice big 17" screen, and dual SATA drives. Woohoo - different drives for different OS's!

So I got a lightly used VGN-AR290G from eBay, and then found something out...

Those dual hard drives? They're hooked up to an Intel hardware RAID controller, and by default are configured as RAID 1. The upshot?

• You can install Vista.
• You can also install the custom, pre-slipstreamed version of XP Media Center Edition that comes with it - but that's not what I need for development
• You can't install plain old XP Pro, because it doesn't see any disk drives.
• Ubuntu sees both disk drives, and appears to install, but doesn't boot. That's because Ubuntu attempts to install as non-RAID, and then when you boot, the GRUB bootloader is all confused.

There are instructions online for getting Ubuntu installed onto RAID, and somebody claims to have gotten it to work with the 290G with dual boot, but I didn't have much luck. It would rock to have the speed of RAID0 on this thing, but I decided it would be simpler to uncouple the RAID.

And that, as usual, is easier said than done. But to save you the time I spent figuring it out, here's the recipe:

1. Reboot the laptop.
2. When the Sony logo comes on the screen, hold down the F2 key. You can let up when the laptop starts beeping at you. After a few seconds, this will bring you into the BIOS utility.
3. Go to BIOS utility's Advanced tab and switch RAID Configuration to Show (if it's not set to that already). Then save the BIOS configuration and exit. The laptop should now reboot.
   
4. You should now see more boot messages, and eventually get to a screen that shows you the disk configuration. During the few seconds this is up, hold down the Ctrl and I keys at the same time. This should switch the computer into the RAID editor utility.
5. In the RAID utility, from main menu, choose the option to Reset Disks to Non-RAID. Save the configuration and exit.

The most common sequence for setting up an XP/Vista/Linux triple-boot is to partition the drive(s) with gparted, then install XP, Vista, and Linux in that order. But alas, after all this, XP Pro still didn't recognize the hard drives. So I just installed Ubuntu 8.10, since that was my most pressing need, and it now works fine.

My guess is that I'll have to slipstream the RAID driver onto the XP Pro install CD, but that's a job (and a post) for another day.