I had talked about getting started in building the PHP stack last time, now I’m taking it…
One step further
"We should forget about small efficiencies, say about 97% of the time: premature optimization is the root of all evil." – Donald Knuth
A chance conversation I had last summer at OSCON with Trent Nelson—who was building Python on Windows—had planted the seeds of how to get PHP on Windows optimized further. Trent was using the PGO features of Visual Studio to generate Python binaries that run faster. Rather than spend a lot of time optimizing all the little bits of PHP itself, I thought that this would be an ideal way to improve the overall speed of PHP, provided I could find the right scenarios to train PHP with. Little did I know that finding the right scenarios wasn't the hardest part.
|What is PGO? (from Wikipedia)
Profile-guided optimization (PGO) is a compiler optimization technique in computer programming to improve program runtime performance. In contrast to traditional optimization techniques that solely use the source code, PGO uses the results of test runs of the instrumented program to optimize the final generated code. The compiler is used to access data from a sample run of the program across a representative input set. The data indicates which areas of the program are executed more frequently, and which areas are executed less frequently. All optimizations benefit from profile-guided feedback because they are less reliant on heuristics when making compilation decisions.
Adding PGO to the existing build process
"I have not failed, I've just found 10,000 ways that won't work." – Thomas Edison
I had downloaded the source to the dependent libraries off the PHP wiki, checked out the PHP source code, and began the process of adding in PGO support to the existing build process. This proved to be extremely difficult. Even limiting the scope to just the core of PHP itself—without the dependent libraries, I ran trouble trying to compile using PGO instrumentation and then re-linking after running some tests. The make file that gets generated by the configure.js script (a JScript version of the automake configure script for the Windows platform) was just not built with what I had in mind.
I spent the better part of two weeks trying different approaches to tweaking the makefile so that I could use PGO to improve the PHP executable, but I kept running into roadblocks. Worse, the closer I got to a makefile that did that I wanted, the farther away from the current build process I was getting, and I wasn't sure that what I would end up with would even be close to what was being built today.
The long dark winter road
"Only the meek get pinched. The bold survive." – Ferris Bueller
I came to the conclusion that I'd have to build new Visual Studio project files from scratch. What worried me is that this would end up to be a completely different build process and I'd never get the community to abandon what was already working, so I'd better be able to rebuild these new project files easily. I started looking (inside Microsoft and out) for any tools which generated Visual C++ project files. I found someone internally who had used some JScript to create project files from text files, but after some experimentation, I found this was nowhere near what I needed. What I really needed was a way to convert the generated Makefile into a .vcproj file—and not just 'wrap' it.
Once I found there was no such tool* , I began trying to figure out how to create one. I had this idea a few times in the last decade or so: watch how a program was compiled, and create a project file that does the same thing. Having tossed around the idea in my head before, I knew it wasn't going to be trivial, but without it, I couldn't do what needed to be done.
|* Let me tell you: you never want to think about writing a tool to parse out what a makefile does. It's rather like making a tool that tells you how sausage is made, in excruciating detail. Ugh.|
In Part III, I’ll talk about the trouble with observing the build process.