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AMD and SuSE Porting Linux to Sledgehammer
-|Oblom|- writes "AMD has partnered with SUSE to port Linux to its upcoming 64-bit Sledgehammer chip. The story is on CNET and the projects site is here www.x86-64.org Well... I have been waiting for a while for this announcment. Hopefully by the end of next year I'll be running dual-core 1.5Ghz(at least) Sledgehammer with Linux on it"
The reason to switch to 64 bits is not performance. Extra bits don't give you more speed. It only increases what you can do (which might possibly give more speed, but generally wider datapaths are slower, not faster).
The most important reason to want 64 bits is for server applications which want an address space larger than 4GB. 64 bits of virtual address space is the main attraction of these chips, and only for servers. Which is why Sledgehammer is being pushed as a server-only proc to compete with Merced.
You might get other benefits, like 64 bit integer ops being faster (but not necessarily... adequate bypass networks in a 32-bit proc might make this a wash). Which is only a benefit if your app uses lots of 64 bit integer ops.
There are also penalties -- for example, the page table hierarchy has 4 levels, which means more memory accesses on a TLB miss.
16->32 was different, because it also gave you all kinds of benefits like protected mode, virtual memory, and other stuff i'm too lazy to remember.
And 16 bits was never really enough.
Anyway, the point is that there is no real reason to worry about current apps moving to 64 bits when Sledge hits. Those server apps that will benefit will switch, and those that won't have no reason to (which is the true beauty of this processor).
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