Onboard System Memory Cache May Affect Profile Times

MS-DOS               | OS/2

The information in this article applies to:

• Microsoft Source Profiler for MS-DOS, versions 1.0, 1.0a, 1.2, and 1.3
• Microsoft Source Profiler for Windows, versions 1.0, 1.0a, 1.2, and 1.3
• Microsoft Source Profiler for OS/2, versions 1.0, 1.0a, and 1.2

The information in this article is included in the documentation starting with Visual C++ 5.0. Look there for future revisions.

SUMMARY

The Microsoft Source Profiler may display erratic execution times on any system with an Intel 80386 or 80486 processor that has a built-in memory cache. This is noted in the Operating-System Notes in the "Microsoft Source Profiler User's Guide" and in the Profiler online help. The only real workaround is to disable the cache, because there is no way to control what is cached and what is not cached.

MORE INFORMATION

The erratic profile results are caused by the way a memory cache of this type operates. If code from the program being profiled is in the cache, the execution times will be less than normal. On the other hand, it's likely that the cache will be dominated by the Profiler itself, since the instructions from the Profiler's own code will usually be in the cache. This may then result in increased times for the program being profiled. Caching will also affect small programs more than large ones due to the successful hit rate in the cache.

Because memory caching hinders accurate profiling, a system without a cache should be used while profiling to ensure the most reliable times. In any case, the overall effect of a cached system should be that it runs faster, so it should not be necessary to consider this net gain when profiling.