Performance is slow on Lion 64-bit

[krblock]

I recently tried using mach_override.c on Lion 64-bit and the performance was a lot slower than in previous OS versions on 32-bit. Based on some performance measurements I determine that the performance problem was due to a large number of calls to vm_allocate in the following snippet of code from allocateBrandIsland. In previous versions vm_allocate was only called once, but on Lion 64-bit is was called around 64K times.

        while( !err && !allocated && page != last ) {

            err = vm_allocate( task_self, &page, pageSize, 0 );
            if( err == err_none )
                allocated = 1;
            else if( err == KERN_NO_SPACE ) {

if defined(x86_64)

                page -= pageSize;

else

                page += pageSize;

endif

                err = err_none;
            }
        }

Not sure what the idea solution would be, however, I made two changes that greatly improved performance for me:

1. I cached the last call, if the same "first" address is used, I started at the next available page based on the last call.
2. When not using a cached call, make larger jumps through memory to find an available page quicker.

The changes where the following where COVERITY macro enables the change:

--- 1.15/build/capture/mach-override.c 2012-01-28 12:54:07 -08:00
+++ 1.16/build/capture/mach-override.c 2012-01-28 13:50:08 -08:00
@@ -361,6 +361,11 @@ mach_override_ptr(

    ************************************************************************

***/

+#if COVERITY
+static vm_address_t lastFunctionAddr = 0;
+static vm_address_t cacheAddrFirst = 0;
+#endif
+
mach_error_t
allocateBranchIsland(
BranchIsland **island,
@@ -389,7 +394,26 @@ allocateBranchIsland(
vm_address_t last = 0xfffe0000;
#endif

+#if COVERITY

•  /\* If we are starting from the same address again, skip ahead to where we
  

•     found the address last time. */
  

•  int using_cache = FALSE;
  

•                   vm_address_t page;
  

•  if (lastFunctionAddr == first) {
  

•    using_cache = TRUE;
  

  +#if defined(x86_64)

•    page = cacheAddrFirst - pageSize;
  

  +#else

•    page = cacheAddrFirst + pageSize;
  

  +#endif

•  }
  

•  else {
  

•    page = first;
  

•  }
  

  +#else
  vm_address_t page = first;
  +#endif
  +
  int allocated = 0;
  vm_map_t task_self = mach_task_self();

@@ -400,15 +424,30 @@ allocateBranchIsland(
allocated = 1;
else if( err == KERN_NO_SPACE ) {
#if defined(x86_64)
+#if COVERITY

•      /\* If we are not using a cached value, the memory we want could be fa
  

  r away.

•         Take bigger jumps */
  

•                                   page -= (using_cache ? pageSize : pageSi
  

  ze*64);
  +#else
  page -= pageSize;
  +#endif
  #else
  page += pageSize;
  #endif
  err = err_none;
  }
  }
  +

+#if COVERITY

•  if( allocated ) {
  

•    lastFunctionAddr = first;
  

•    cacheAddrFirst = page;
  

•    _island = (BranchIsland_) page;
  

•  }
  

  +#else
  if( allocated )
  island = (BranchIsland) page;
  +#endif