WBINVD instruction usage

Question

I'm trying to use the WBINV instruction on linux to clear the processor's L1 cache.

The following program compiles, but produces a segmentation fault when I try to run it.

int main() {asm ("wbinvd"); return 1;}

I'm using gcc 4.4.3 and run Linux kernel 2.6.32-33 on my x86 box.

Processor info: Intel(R) Core(TM)2 Duo CPU T5270 @ 1.40GHz

I built the program as follows:

$ gcc

$ ./a.out

Segmentation Fault

Can somebody tell me what I'm doing wrong? How do I get this to run?

P.S: I'm running a few performance tests and want to ensure that the previous content of the processor cache does not influence the results.

Answer 1

Quoting from Intel® 64 and IA-32 Architectures Software Developer's Manual Combined Volumes 2A and 2B: Instruction Set Reference, A-Z:

The WBINVD instruction is a privileged instruction. When the processor is running in protected mode, the CPL of a program or procedure must be 0 to execute this instruction.

In other words only kernel mode code is allowed to execute it.

EDIT: Previous SO discussion on clearing caches:

"C" programmatically clear L2 cache on Linux machines

How can I do a CPU cache flush in x86 Windows?

How to clear CPU L1 and L2 cache

https://stackoverflow.com/questions/3443130/how-to-clear-cpu-l1-and-l2-cache