Systematic Gaming

November 23, 2008

Patterns in Performance – Cache Manipulation

Filed under: optimization — Tags: , — systematicgaming @ 2:37 am

With modern processors greatly outpacing the speed of memory we need to properly utilize the memory cache to achieve high performance.  Whenever we touch a memory address, the memory is pulled into the cache from main memory.  This is a slow operation, taking hundreds of cycles on modern CPUs.

To address this problem we’ll look at another pattern in performance: cache manipulation.  Instead of waiting for the memory controller to fetch memory when at the time we access it, we tell the memory controller to fetch the memory in advance.  By the time we need the memory it has already been put into the cache.

[EDIT: Updated to more correctly show load-wait timings.  Loads cause stalls when the loaded data is first accessed, not when the load instruction is invoked (which is what was previously implied).]



November 7, 2008

Patterns in Performance – Caching

Filed under: optimization — Tags: , — systematicgaming @ 4:20 am

When optimizing code there are a number of techniques than are frequently used – tried and true methods to speed up our code.  These optimization patterns occur again and again.  In this series we’ll look at various patterns in performance than we can apply in numerous situations.

Almost all programming can be viewed as an exercise in caching – Terje Mathisen

The first pattern we’ll look at is caching.  Caching is simply storing the result of calculations for later use.  This is a traditional space-time trade-off, where we use a limited amount of memory to reduce recalculating functions, trading memory of speed.

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