On Tue, 28 Jul 2009, Dave Youatt wrote:
Unlikely. Different threads on the same CPU core share their resources, so they don't need an explicit communication channel at all (I'm simplifying massively here). A real interconnect is only needed between CPUs and between different cores on a CPU, and of course to the outside world. Scott's explanation of why SMT works better now is much more likely to be the real reason.
Actually, no, I wrote that. Please give at least some indication when replying to an email which parts of it are your words and which are quotes from someone else. Emails can be incredibly confusing without that distinction.
You actually wrote:
:-) there's also this interconnect thingie between sockets, cores and memory. Nehalem has a new one (for Intel), integrated memory controller, that is. And a new on-chip cache organization.
This, (like I mention elsewhere) will make the CPU faster overall, but is unlikely to increase the performance gain of switching SMT on. In fact, having a lower latency memory controller is more likely to reduce some of the problem that SMT is trying to address - that of a single thread stalling on memory access.
Having said that, memory access latency is not scaling as quickly as CPU speed, so over time SMT is going to get more important.
Matthew -- "Take care that thou useth the proper method when thou taketh the measure of high-voltage circuits so that thou doth not incinerate both thee and the meter; for verily, though thou has no account number and can be easily replaced, the meter doth have one, and as a consequence, bringeth much woe upon the Supply Department." -- The Ten Commandments of Electronics -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
