Mikulas Patocka wrote:
On Mon, 15 Oct 2007, H. Peter Anvin wrote:
Mikulas Patocka wrote:
I know about unordered stores (movnti & similar) --- they basically use
write-combining method on memory that is normally write-back --- and they
need sfence. But which one instruction does unordered load and needs
lefence?
PREFETCHNTA.
PREFETCH* doesn't change program semantics. The processor is allowed to
ignore prefetch instruction if it doesn't have resources needed for
prefetch. It not ordered wrt. fences.
PREFETCHNTA was implemented as prefetch into L1 cache and omitting L2
cache on Pentium 3 and M --- and it is implemented as prefetch into L2
cache on other --- do it doesn't really use any special buffers.
It's semantics allows it to, though. It's not clear to me whether it is
actually necessary on existing chips.
It does, I believe, way-restricted prefetch on existing silicon.
-hpa
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