On Tue, 26 Jul 2011, Andriy Gapon wrote:
Can anybody explain to me why our _x86_ SMP topology discovery and reporting
code sometimes reports "HTT" and sometimes "SMT"? As in FreeBSD/SMP: %d
package(s) x %d core(s) x %d HTT threads vs FreeBSD/SMP: %d package(s) x %d
core(s) x %d SMT threads
As I understand, and quoting Wikipedia (I know, I know), SMT stands for
simultaneous multithreading and is a generic term for a particular kind of
hardware multithreading:
http://en.wikipedia.org/wiki/Simultaneous_multithreading
The only known (to me) implementation of SMT for x86 is Intel's
Hyper-Threading Technology aka HTT aka HT Technology aka hyperthreading:
http://en.wikipedia.org/wiki/Hyper-threading
http://software.intel.com/en-us/articles/intel-hyper-threading-technology-your-questions-answered/?wapkw=%28Intel+Hyper-Threading+Technology%29
Several MIPS platforms we run on support SMT. Typically this means a set of
"weaker" threads sharing a single core, usually context switching as a result
of memory access stalls in other threads, and perhaps sharing particularly
expensive CPU features, such as a TLB. They sometimes come with
high-performance message-passing facilities between threads, or even between
cores, to supplement shared memory and IPIs.
It may be that HTT is, among other things, a trademark of Intel.
Robert
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