On Feb 21, 2012, at 3:49 PM, Dave McGuire wrote:
On 02/21/2012 03:04 PM, David Riley wrote:
I have a 4-core i7 which masquerades as 8 due to
hyperthreading
(which they actually got right in the i7, as opposed to the P4). I
don't see a *lot* of difference between 9 and 12 jobs.
Oh dear, the replay mechanism problem? Wow what a mess that was! I had assumed
they'd fixed that by now; I'm glad to hear that they really did. (typing this on a
screaming fast i7 just like yours...it's about time x86 processors got almost as fast
as my UltraSPARCs, even though they require 3x the clock rate to do it!)
Well, after the P4 mess, they just dropped it from the original Core architecture (which
was a complete reboot from the mess that was the P4). They added it back in on the i7
family, and it does help a bit; I get something like a 30% speedup on my simple raytracer
running 8 threads instead of 4, and that's basically CPU and memory bound (very, very
little I/O and system call overhead; no thread locks except for getting the next pixel
position, even). ISTR that hyperthreading generally imposed a performance *penalty* on
the P4.
- Dave