Multicore hypothetical question

This will sound crazy. I see lots of maps with insane levels of detail, and I doubt that having a multicore processor would help. It looks like single thread performance is a thing of the past, with slow-clocked multicore processors becoming popular.

Do you worry that "modern" hardware will struggle to play Doom after a while? I think a 1024 core processor running each at 40 Mhz might be nice to play Half Life 13, but I somehow doubt if it could play Doom well.

Am I crazy?

The new Intel Core CPU's are very fast indeed for single-threaded code. Just because something is "slow clocked" doesn't mean it's any slower, just that it has to do more during each cycle to get equivalent performance. Intel hit a thermal brick wall with the P4 where it became impossible to increase frequency much higher without the CPU requiring absurd cooling solutions, so they moved back to more reasonable CPU designs. The Core architecture operates at much lower frequencies but still manages to be considerably faster. I doubt we would see a consumer CPU that trades single-thread execution speed for more cores.

The vast majority of code doesn't have enough parallelism to use 1024 cores, let alone 4 or even 2 in some cases. The CPU's with massive number of cores are designed for server duties or other specialty applications. And just to show that not everyone in the server market is going the route of having multiple low-clock cores, IBM is pushing for 5GHz+ with the Power6.

I don't think Doom or games in general have much to worry about.

Even the most rigid single threaded application will have enough system code so that the second core won't be wasted. For example think of a music player running in the background.

And of course mere clock frequency doesn't tell anything whatsoever about performance. Just compare AMD's processors with Intel's old ones. The clock frequency was considerably lower but performance was equal.

Yet there's still people out there that believe the old fairy tale of more clock cycles -> more speed.

Even now, AMD is considering other avenues to gain processing power other than multiple cores.

Cool. But is there ever a possibility of new hardware making Doom impossible? I heard our CPUs are all x86 and will be replaced by x87 someday.

I doubt that a coprocessor alone will be able to do much! :D

Bucket said:

Even now, AMD is considering other avenues to gain processing power other than multiple cores.

So? Intel has already succeeded.

Graf Zahl said:
Yet there's still people out there that believe the old fairy tale of more clock cycles -> more speed.

Yeah, what do anti-Mac people do now that Apple is using Intel processors?

Almost everything is still single-threaded, because writing highly multithreaded code is incredibly difficult. No company in their right mind would release a processor with 1024 cores but running at an incredibly slow speed.

On the other hand, all SDL programs are automatically multithreaded, so those will theoretically run better on multi-core processors. This would include a whole lot of Doom ports ;)

Quasar said:

On the other hand, all SDL programs are automatically multithreaded.

Automatically multithreading the application code itself should still be considered a miracle. ;)

So what does it multithread? Probably only the stuff non-SDL applications don't have in the first place.

I'm really not sure. I just know EE has something like five separate threads, only one of which is the main application. The rest belong to SDL. If those could hog cycles on a separate core, the main program would get more time. Of course it's not like Doom *needs* this. The thought of it is just cool ;)

Quasar said:

I'm really not sure. I just know EE has something like five separate threads, only one of which is the main application.

Only 5? When I break GZDoom I get 8 - without SDL ;) Not that it means much. Most are background tasks that only run for short periods of time. The biggest one of them is the music player.

So, is there any part of Doom that would benefit from some added parallelism? I've read about what Valve did with the Source engine to allow it to take advantage of multicore machines, and I'm curious how much (if anything) of that applies to something like Doom.

(Obviously Doom runs great even on modest CPUs, but let's ignore that)

Higher Game said:

Do you worry that "modern" hardware will struggle to play Doom after a while? I think a 1024 core processor running each at 40 Mhz might be nice to play Half Life 13, but I somehow doubt if it could play Doom well.

Am I crazy?

1024 cores at 40 MHz? D00d, multicore in its present form is slapping or 4 slightly modified "normal" cores on the same chip and calling it a "double" or "quad core", quite far from making a cluster of 1024 486-like processors. Even if that was the case, for whatever crazy and extreme reason, it would STILL be able to run Doom even on one core (remember the original doom specs)?

Now in general, the original DOOM code didn't use any kind of "real" multithreading (e.g. POSIX) but used internal asynchronous timeslicing e.g. for overlaying menus or interrupt based for playing back samples and midi music "so fast that you thought it was uninterruptible".

A "true" multithreaded port would of course delegate those tasks to "real" threads and would perhaps benefit a bit from an extra core, but the bulk of the game (rendering and movement) would still live happily in one thread, unless some port implements some super-duper monster AI.

The only real use for that kind of thing is scientific calculations, which use lots of massively parallel data processing. Games won't benefit from it nearly as much, and they are much more difficult to program in such a way. ::coughPS3cough::

Read this : http://en.wikipedia.org/wiki/Parallel_computing

Despite the tech stuff that I don't understand in all it's points, you forget that you choose if upload your hardware or not. For most of us, to update the hardware is a measure to play newer games, personaly I'll don't play any game that should require me to abandon vanilla DOOM exes (I have a dual boot to run XP and 98, but I'd never installed DOOM 3 if it required me to move to XP in a permanent way), not to mention that newer games while fun and all (not allways) tend to be droped once you beat them up, so no way. Ok, that's my opinion.