Basic skills to work as an optimiser in the gaming industry

Question

I'm curious about a certain job title, that of "senior developer with a specialty in optimisation." It's not the actual title but that's essentially what it would be. What would this mean in the gaming industry in terms of knowledge and skills? I would assume basic stuff like

• B-trees
• Path finding
• Algorithmic analysis
• Memory management
• Threading (and related topics like thread safety, atomicity, etc)

But this is only me conjecturing. What would be the real-life (and academic) basic knowledge required for such a job?

Answer 1

I interviewed for such a position a few years ago at one of the Big North American game studios.

The job required a lot of deep pipeline assembly programming, arithmetic optimization algorithms (think Duff's Device, branchless ifs), compile-time computation (SWAR), meta-template programming, computation of many values at once in parallel in very large registers (I forget the name for that)... You'll need to be solid on operating system fundementals, low level system operations, linear algebra, and C++ especially templates. You'll also become very familiar with the peculiar architecture of the PlayStation3, and probably be involved in developing libraries for that environment that the company's game teams will build on top of.

Answer 2

This is one of those "if you got it you know it" type of things. It's hard to list out specifics, and some studios will have different criteria than others.

To put it simply, the 'Senior Developer' part means you've been around the block; you have multiple years of experience in which you've excelled and have shipped games. You should have a working knowledge of a wide range of topics, with things such as memory management high up the list.

"Specialty in Optimization" essentially means that you know how to make a game run faster. You've already spent a significant amount of time successfully optimizing games which have shipped. You should have a wide knowledge of algorithms, 3d rendering (a lot of time is spent rendering), cpu intrinsics, memory management, and others. You should also typically have an in depth knowledge of the hardware you'd be working on (optimizing PS3 can be substantially different than optimizing for PC).

This is at best a starting point for understanding. The key is having significant real world experience in the topic; at a senior level it should preferably be from working on titles that have shipped.

Answer 3

Generally I concur with Ether's post; this will typically be more about low-level optimisation than algorithmic stuff. Knowing good algorithms comes in handy, but there are many cases in games where you prefer the O(N) solution over the O(logN) solution because the first is far friendlier on the cache and requires less memory management. So you need a more holistic knowledge.

Perhaps on a more general level, the job may want to know if you can do some or all of the following:

• use a CPU profiler (eg. VTune, CodeAnalyst) in both sampling and call graph mode;
• use graphical profilers (eg. Microsoft Pix, NVPerfHud)
• write your own profiling/timer code and generate useful output with it;
• rewrite functions to remove dynamic memory allocations;
• reorganise and reduce data to be more cache-friendly;
• reorganise data to make it more SIMD-friendly;
• edit graphics shaders to use fewer and cheaper instructions;

...and more, I'm sure.

Answer 4

This is a lot like my job actually. Real-life knowledge that would be practical for this:

• Experience in using profilers of all kinds to locate bottlenecks.
• Experience and skill in determining the reason those bottlenecks exist.
• Good understanding of CPU caches, virtual memory, and common bottlenecks such as load-hit-store penalties, L2 misses, floating point code, etc.
• Good understanding of multithreading and both lockless and locking solutions.
• Good understanding of HLSL and graphics programming, including linear algebra.
• Good understanding of SIMD techniques and the specific SIMD interfaces on relevant hardware (paired singles, VMX, SSE/MMX).
• Good understanding of the assembly language used on relevant hardware. If writing assembly, a good understanding of instruction pairing, branch prediction, delay slots (if applicable), and any and all applicable stalls on the target platform.
• Good understanding of the compilation and linking process, binary formats used on the target hardware, and tools to manipulate all of the above (including available compiler flags and optimizations).

Every once in a while people ask how to become good at low-level optimization. There are a few good sources of info, mostly proprietary, but I think it generally comes down to experience.