Hidden SMT support in Tiger

[hmurchison]

Ars Technica- The definitive monster 970 thread (http://episteme.arstechnica.com/eve/ubb.x?q=Y&a=tpc&s=50009562&f=8300945231&m=9080959175&p=100)

Originally posted by Catfish_Man42:
Doing sysctl -a in 10.4 turns up two interesting values, specifically the number of physical and logical processors. Since this distinction isn't made in 10.3 (as far as I can tell, anyway) does this imply SMT support in 10.4?

All but guarantees that SMT is coming during Tigers duration as King of the cats. Maybe those Quad Powermac (http://macosrumors.blogspot.com/) rumors have a shred of truth in them :D

[ast3r3x]

Yummmmy. Quad PowerMacs in a year and a half. Just when I should be feeling like I need a new computer :D

Can you imagine these things? They'd fly...hold huge amounts of RAM, cost way too much, but be amazing.

[Moogs]

If a Quad comes out and it's not outrageously priced, that may mark the first time in my Mac using history that I sold a computer that was less than two years old to buy a newer one. Pretty cool.

:)

[DMBand0026]

You actually linked to a MacOsRumors story and expected people to not laugh at it? :lol: :lol:

If they say it, it's almost certain to not happen. But I won't rain on your parade any longer. Continue dreaming :D

[Moogs]

Well, it's not the rumor that's interesting, but the SMT support files that are apparently built into the OS from an early development stage. If those files weren't noticed I'm sure no one would give a second thought to any related rumors. Quad processor Macs are mythical creatures of lore at this point. To even speculate about them without some corroborating evidence is almost comical, as you are aware.

Some people will tell you that you have a better chance of proving the existence of the Loch Ness Monster.

[Luca]

If the next processor Apple uses is an IBM dual-core CPU, then a dual-CPU, dual-core machine would not be too farfetched.

[DMBand0026]

Right, two dual core processors is technically considered a quad processor machine. But I don't think the G5s are going to go dual core. If anything the G6 (in like 2008) will debut as a dual core chip.

But MOSR is talking about 4 physical processors. :no:
There isn't even room for that in the G5, look at the size of the current heat sinks. The whole enclosure would be heat sinks, no room for one optical drive, let alone two like people want. ;)

[hmurchison]

Here's what I think happens.

Apple hits the Dual 3ghz mark with the next Powermac refresh. This will be a 97x G5 based off the POWER5 architecture. It will not be dual core but it will have say 5 more pipeline stages(roughly 20) and support low-k dielectric tech. It will have SMT so we will have our "functional" Quad. Apple will ride this SMT enabled system for a year or year and a half at most before IBM movies to 65nm in which they will move to dual core processors then. The question is whether or not they would keep the SMT on each core. If they did that would totally rock. How's an Octomac sound to you?

What I see is a balancing of todays technology. SMT gives Apple/IBM a reprieve from being forced to go dual core early. SMT allows IBM to increase the pipelines thus hitting 3Ghz easier without taking a huge hit on Instructions Per Cycle(IPC) because SMT will keep the pipelines full with data. SMT is the cheaper option right now that being that it requires much less transistor space than a whole "nother core. That space savings can be put to good use by adding an ondie memory controller. Then when a majority of Mac apps are multi processor aware we move to the next process shrink 65nm which then gives us die space to add those new cores. We're only at 2007 at this time frame. Nice logical progression.

[709]

I like it. I'll be picking up a Rev.C G5 in January '05, and an Octo in Jan '07. :)

[Eugene]

The sysctl variables in question are hw.physicalcpu, hw.physicalcpu_max, hw.logicalcpu, hw.logicalcpu_max ?

Does anybody know if these are in FreeBSD 5.x?

[hmurchison]

The sysctl variables in question are hw.physicalcpu, hw.physicalcpu_max, hw.logicalcpu, hw.logicalcpu_max ?

Does anybody know if these are in FreeBSD 5.x?

Good question. Someone on Ars asked if these files came across from BSD 5.x and Greg from Omnigroup responded:

Apple gets all their Unix tools and daemons from freeBSD, but the kernels of the two systems are _very_ different. Any SMT support would have had to have been a very explicit effort by Apple's software engineers.