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Some users have reported getting strange results for the floating point (FP) division test in PerformanceTest.
The typical symptoms of the problem are the floating point division result varying between a high and low value from one run to the next. The result will typically switch from the low value to the high value if the 3D DirectX tests are run in between runs of the FP division test.
After a long investigation we have discovered that the use of DirectX sets the floating point control register (which is inside the CPU) when DirectX is started but never re-sets the value.
Having the CPU configured differently between runs of the FP division test results in different results.
The floating point control register (also known as the x87 FPU Control word) contains a setting that determines how floating point numbers are rounded to integers. This is the value modified by DirectX.
So in fact the FP division test does in fact report the correct result! However the CPU is varying its speed because the various different rounding options in the CPU impact on the CPUs throughput.
This problem is only in V4.0 of PerformanceTest and only affects the result for FP division result. We have made a code change so that in future versions of PerformanceTest a particular rounding option is forced on.
David
PassMark
The typical symptoms of the problem are the floating point division result varying between a high and low value from one run to the next. The result will typically switch from the low value to the high value if the 3D DirectX tests are run in between runs of the FP division test.
After a long investigation we have discovered that the use of DirectX sets the floating point control register (which is inside the CPU) when DirectX is started but never re-sets the value.
Having the CPU configured differently between runs of the FP division test results in different results.
The floating point control register (also known as the x87 FPU Control word) contains a setting that determines how floating point numbers are rounded to integers. This is the value modified by DirectX.
So in fact the FP division test does in fact report the correct result! However the CPU is varying its speed because the various different rounding options in the CPU impact on the CPUs throughput.
This problem is only in V4.0 of PerformanceTest and only affects the result for FP division result. We have made a code change so that in future versions of PerformanceTest a particular rounding option is forced on.
David
PassMark