@wallstreettech"Proximity" is the watchword for today's capital markets technology. Many organizations are hosting their trading algorithms as close as possible to securities exchanges — often in the exchanges' own colocation centers. The goal is to accelerate automated trades by reducing communication distance. Though the practice can sound far-fetched, given the speed of data packets traveling over fiber optic cables, it speaks volumes about the time scale of today's buying and selling and the competitive advantage of shaving microseconds from the trade cycle.
It is surprising, then, how rarely one hears discussion of another type of latency-inducing distance in trading: the execution path, or the length of the series of instructions that the CPU must complete to perform a task. Like physical distance in the example above, the time overhead imposed by CPU instructions appears insignificant on a small scale. Processor speeds are routinely measured in billions of instructions per second, after all.
Better Than Colocation
But automated trading and other real-time capital markets functions are computationally intensive — they burn through instructions by the millions or even billions. And compared to physical distance, execution path is supremely malleable. Once you colocate your system, you can't reduce physical distance further — and you enjoy no advantage over competitors that also have colocated. However, significant efficiency gains can result from many types of changes to software, ranging from fine-tuning bits of code (the efficiency gap between a switch/case and an if/then/else statement used in an algorithm can start to matter, when repeated thousands of times in a looping function) to complete redesigns of systems and applications.
Another advantage of a short execution path is that it increases the likelihood a code segment will already be in L1/L2 cache when needed by the CPU. When the system encounters an instruction that isn't already in the cache, it must retrieve that instruction from main memory — and this becomes a performance bottleneck. In a system with a 2.4 gigahertz CPU and a 400 megahertz front-side bus, for example, fetching from memory is the equivalent of speeding down the Autobahn at 240 kph, then having to slow down to 40 kph for an obstacle, then racing to the next obstacle at 240 kph.
To grasp the computational intensiveness of real-time capital markets, consider the risk management function within an algorithmic trading system. This code executes at the moment an order is placed and determines whether or not to allow the trade. Risk management algorithms sort and filter a flood of information, acquiring needed data points and applying complex math to assess risk along dozens of parameters. Because it must execute before a trade completes, risk management code is time-critical, and the amount of data that must be processed to accomplish its objective is growing, due to factors such as exchanges' expanding data broadcasts.
To continue with the example, let's say a firm's goal is to cut risk management latency in order to reduce order-processing time to below 1 millisecond. On hardware that can process 10 billion instructions per second — and excluding other factors that affect latency — the 1 millisecond limit sets the maximum allowable execution path for order-processing at 10 million instructions. Now, let's say that through clever programming, the firm improves software efficiency to achieve order-processing latency that is 35 percent faster than this limit — in other words, it cuts 350 microseconds from the processing time (or it can handle 3.5 million more instructions in the same time).
How does this compare to colocation's advantages? Packets travel over fiber optic cable at the speed of light, less some amount determined by the cable's index of refraction — 124,274 miles per second often is cited as a rule-of-thumb speed. At that rate, and all other factors being equal, the 35 percent gain in code efficiency equates to slicing about 43 miles from physical distance, which is well beyond the 25 mile minimum said to motivate firms' colocation decisions.
