How does vista use multicores

fieseler · May 26, 2009

Lets say im playing a game that can use the 2 cores from a c2 duo, and i have a quad core. While im gaming, what would the other 2 cores do? I would of imagined that background services/processes would use the cores with less load, but somehow i cant imagine that being so. Also how would vista use a quad core cpu while im messing around on the desktop.

I ask coz im considering getting a quad core so im maxing my socket 775 board out before having to migrate to i7. I dont do any 3ds max or anything so im trying to figure out if there would be any actual advantages in my situation.

I considered going for a higher clocked dual core, but an extra 600mhz isnt worth a new processor purchase. Also figured that gta4 might be able to run as well.

H2SO4 · May 26, 2009

Oooh, an interesting question, although it's probably not getting the attention it deserves in this section

To understand how this stuff works, it's necessary to distinguish between a "process" and a "thread":

THREAD: a sequential stream of instructions that a processor can execute. A thread completely monopolises a processor (core) until that thread is "pre-empted" by the OS so that another thread can get its fair share of processor time. That period is called a "quantum" and its on the order of 10 to 15 milliseconds.

PROCESS: A grouping of one or more threads. They share the same virtual memory, and the same security token, but each thread remains a distinct set of instructions.

At any time, there may be no threads in a read-to-run (RTR) state, in which case the processors run threads belonging to a special "idle" process, or there may be one thread, or many. An OS component called the thread dispatcher has the job of looking at all the RTR threads and "scheduling" them across the available processors. It takes into account thread priority, the processor where a particular thread last ran (there's cache advantages from staying on the same proc), and other factors to continuously make decisions about which threads get to run on which processors.

The dispatcher is blind to process boundaries. It only cares about threads. If a process has 17 threads and another process only has 2, the first one will get 17/2 times the processor love, everything else being equal. Processes that form part of the OS itself have hundreds of threads between them, and by the time you add all apps there'll be tens or hundreds more, but the real question is just how many of them are RTR at any time...

If you have a game that can spawn 4 or more computationally-intensive threads that are generally RTR all the time, all 4 cores in a quad-core proc should stay busy, although they'll sometimes be temporarily diverted to handle the OS threads and any other apps which may be vying for processor time. Otherwise, if the game only spawns 1 or 2 RTR threads - a much more common scenario - the other cores will sit and do very little other than background maintenance tasks.

The short answer is "get a quad core if you can easily afford it". Your life won't be made any easier or simpler, but sometimes you'll wait a little less, plus the machine will last and be relevant somewhat longer.

corei7 · May 27, 2009

I had the same question in my mind, I believe in gaming 1 handles graphics the other handles processing stuff and so on.

fieseler · May 27, 2009

so while in a game that uses dual core, vista would use the other 2 cores for background processes like services and defragging?

This is interesting coz then the 2 cores running the game wouldnt be interfered by the O/S as much.

Right now im deciding between q9550 and e8500, there a £50 difference but £150 isnt really worth 500mhz clock speed and a die shrink so im leaning towards the quad.

H2SO4 · May 27, 2009

fieseler said:
so while in a game that uses dual core, vista would use the other 2 cores for background processes like services and defragging?

Yes, in a nutshell. The two threads spawned by the game process don't own the processors in any way, and it's still possible for other threads running at a higher priority to temporarily take over, but that won't happen while cores 3 and 4 are twiddling their thumbs.

fieseler said:
This is interesting coz then the 2 cores running the game wouldnt be interfered by the O/S as much.

Each core is like an employee - they'll do whatever the management (the OS thread dispatcher) tells them to do. Obviously, more people means more work gets done overall, as long as the influx of work is sufficient to keep all 4 busy. Hence, a quad can easily out-perform a dual core if there are lots of apps (meaning lots of RTR threads), but its advantage with simpler workloads will not be as marked - if there's only ever one work item at a time, the fact that 4 employees are available doesn't speed things up since they can't share a single work item (thread).

fieseler · May 27, 2009

may as well go for a q9550 then. My only concern now is what the temps would be like. I live in the uk and have a well ventilated case, my e6700 (65nm btw) idles around 36c during the summer, Load is around 55c.

Id guess they would be about the same as clock speed is equal, 2 cores extra but the shrink to 45nm would see lower temps i suppose.

thepizzaman · May 27, 2009

no no no! go get the phenom II :P

H2SO4 · May 27, 2009

fieseler said:
may as well go for a q9550 then. My only concern now is what the temps would be like. I live in the uk and have a well ventilated case, my e6700 (65nm btw) idles around 36c during the summer, Load is around 55c.

Id guess they would be about the same as clock speed is equal, 2 cores extra but the shrink to 45nm would see lower temps i suppose.

There are only two temperature ranges where processors are concerned: "good enough" and "over the design limit". As long as the level of cooling in your machine always ensures that the processors always remain in the first category, there's no need to worry.

My visits to the UK lead me to believe that ambient heat is rarely an issue (!), so as long as the case is not covered in a black plastic shroud even the stock cooler should be perfectly adequate on any of these processors. That's what they're designed for

smarteyeball · May 28, 2009

fieseler said:
may as well go for a q9550 then. My only concern now is what the temps would be like

Very similar to what you're getting now and all within the 'good enough' range

H2SO4 said:
even the stock cooler should be perfectly adequate on any of these processors. That's what they're designed for

....unless your overclocking the chip (and the q9xx series overclocks nicely as well). But stock speeds+stock cooler=fine.

avgwarhawk · May 28, 2009

Get the Phenom 9850...OK, I'm partial to those because I have them. Go for the Phenom II. They run cool with stock fans etc. I have mine upgraded just a bit but you know stock cooling is fine if not AMD would be replacing burnt chips all day long. That is not good business sense.

fieseler · May 29, 2009

Its defiantly worth it as ive found a lot of my games can actually use 4 cores. Also wont break the bank trying to cool it as well which is great news.

think ill wait until summer is over b4 i start changing my pc, i was cleaning some of the dust out of the case and due to the heat was sweating like mad. Made a right mess of the shiny finish.

Will yorkfields still be widely available by that time?

Everlong · May 29, 2009

Most likely they will. I'm planning to upgrade to a Q9550 or a Q9650 around October/November to buy myself something for my birthday

There's apparently going to be a price drop on all Intel CPUs as well when the i7 975 is released.

fieseler · May 29, 2009

price drop would be cool, might even be able to go for q9650.

How does vista use multicores

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