AllocatePrefetchDistance is not changed by command line

On Intel SandyBridge Linux x86_64, I tried to increase the AllocatePrefetchDistance by adding:
-XX:AllocatePrefetchDistance=256 -XX:AllocatePrefetchLines=4

But the final flag indicates:
     intx AllocatePrefetchDistance := 192 {product}
     intx AllocatePrefetchInstr = 0 {product}
     intx AllocatePrefetchLines := 4 {product}
     intx AllocatePrefetchStepSize = 64 {product}
     intx AllocatePrefetchStyle = 1 {product}

In vm_version_x86.hpp:
  AllocatePrefetchDistance = allocate_prefetch_distance();
  AllocatePrefetchStyle = allocate_prefetch_style();

  if( is_intel() && cpu_family() == 6 && supports_sse3() ) {
    if( AllocatePrefetchStyle == 2 ) { // watermark prefetching on Core
#ifdef _LP64
      AllocatePrefetchDistance = 384;
#else
      AllocatePrefetchDistance = 320;
#endif
    }
    if( supports_sse4_2() && supports_ht() ) { // Nehalem based cpus
      AllocatePrefetchDistance = 192;
      AllocatePrefetchLines = 4;
#ifdef COMPILER2
      if (AggressiveOpts && FLAG_IS_DEFAULT(UseFPUForSpilling)) {
        FLAG_SET_DEFAULT(UseFPUForSpilling, true);
      }
#endif
    }
  }
  assert(AllocatePrefetchDistance % AllocatePrefetchStepSize == 0, "invalid value");

AllocatePrefetchDistance is decided by the platform, not from command line