Re: Adjusting PC Hyperthreading for Spice Simulation

On Sat, 24 Jan 2009 19:39:32 +0000, Nobody wrote:

In other words... you get 1 billion operations per second (or whatever).
Hyperthreaded CPUs just give the appearance of two CPUs so that if a
particular thread is waiting on, e.g., a memory read from DRAM (this
can take hundreds of cycles)

Memory access taking hundreds of cycles? Hell not even a dozen.

It depends how fast your RAM is. At one point (I guess around 5 years
ago), 350 CPU cycles for a code cache miss was not atypical, but RAM
speed has been consistently increasing faster than CPU speed for the
last few years.

To remove a possible source of confusion: cycle "costs" take into account
the fact that each core can execute multiple instructions concurrently
(superscalar architecture). So a cost of e.g. "100 cycles" refers to a
delay in which a sequence of instructions totalling 100 cycles could be
executed, not 100 times the CPU clock period.

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