Shawn Walker wrote: > On Dec 20, 2007 11:17 AM, Stefan Teleman <Stefan.Teleman at sun.com> wrote: >> >> Marcelo H Majczak wrote: >>> Regarding the i386, why is it -xchip=pentium4 and -xcache=8/64/4:256/128/8 ? >>> The cache seems under specd for most recent chips while pentium4 leaves the >>> pentium mobile out (pentium3)... >> Pentium M is a P3 ? > > It is essentially the same as a P3, but has very different performance > characteristics. > > There was a Mobile version of the Pentium 4 as well (I have one at > home unfortunately).
On Pentium M class processors, cpuid with %eax set to 0 returns 02H/80000004H, which is identical for Pentium 4, Intel Xeon and Pentium M. For all practical purposes, these three processors are indistinguishable from each other. For Pentium 3, cpuid returns 03H. Therefore, Pentium M identifies itself as a Pentium 4 class processor, and not Pentium 3 (which does not return the Extented Function Information). >>> Now an honest question, what is the impact of under specing the cache? >> Less chances of cache thrashing for CPU's with a smaller L2. > > I wonder what the value of specing the cache out is. Isn't studio > capable of selecting the appropriate value on its own? It will select the best cache ratios for the particular CPU you are compiling on. This may be different, and inappropriate, for someone else's box running the same bits. --Stefan -- Stefan Teleman Sun Microsystems, Inc. Stefan.Teleman at Sun.COM
