Which CPUs do you love or hate

[stefcep2]

I even notice a massive difference on my lowly AMD64x2 especially in some games that seem to make good use of dual core .

And when they can have an operating system that is able to perform operating system tasks in parallel thats when we'll really feel the benefits of multiple cores.

[stefcep2]

Single core CPUs were never a good idea, especially when we started to demand multitasking...

It never bothered me when multitasking on my Cyberstorm 68060 single core..

[stefcep2]

Well, the only situation now where multicore is a burden is when using an operating system that can't use more than one core... So I guess that is rather ironicaly probably only AmigaOS now...

Depends on what your definition of "an operating system using more than one core" is

What would interest me more than just having one program crunching numbers within one core, another crunching numbers in another core, a third crunching numbers in a third core etc is if the operating system itself could could be split across the cores running a different task in each core, or i could get one program to split itself across each core.  I hardly ever need to encode more than on video/dvd at the same time, but I'd like to have four cores all working to decode that single DVD at the same time.  At the moment this doesn't happen particularly  well, if at all, as most software and the OS is not designed to detach into parallel tasks like that. Most benchmarks I've seen from dual core systems are at best 30-50% faster than a single core at the same clock speed, and for some benchmarks with some dual core cpu's the dual core can even be slower.  (Windows 7 might be better, i haven't had any experience with it)

[stefcep2]

I dunno where you are getting your impression from  

from this:

 For example, on my machine, a single-thread process using 100% cpu load is actually distributed across all four cores ****(although only one one of them at any instant)****, spending approximately the same amount of time on each one.

and this

***Programs must be written to support this. ****

and this

The next generation of C++ aims to include language-level support for writing multithreaded code, which will certainly help.

hence my statement that multi-core CPU's aren't used particularly well at this time.

[stefcep2]

Wait, hang on. That was given in answer to your earlier point. Didn't you say you'd prefer it if the OS distributed the work between the cores? Well, that's exactly what the kernel does do. To the extent that even a single thread will move from one core to another depending on the existing load on each core and for improved thermal distribution (if nothing else).

A single thread of execution, by definition cannot run on several cores concurrently. Do not confuse multi core with superscalar execution. They are not the same thing and for what it's worth, each of these multiple cores is superscalar and nicely pipelined too. Each one is thus executing more than one sequential instruction in whichever thread they happen to be executing at any instant.

Now, as for the issue about writing stuff for multi core, you have to accept that not every computational task is parallelisable. Therefore there will be some things that cannot on their own take advantage of more than one core. However, you must bear in mind that on all multitasking operating systems there are usually many threads that are ready to run and the scheduler has to pick just one of them per quantum. Not so on a multicore. It will allow as many threads to execute per quantum as the hardware will allow. From a throughput perspective, running four threads in one quantum is up to 4x faster (assuming no interdependencies) than running one each for four successive quantums. Better throughput means less latency for all tasks.

What I am saying is, that unless you use a single application on a single-tasking "OS" (or MacOS classic as it's more commonly known :lol:), it's impossible to not reap a performance gain from multi core in general use.

The principal exception to this rule is when you want to run a single, very CPU intensive task that cannot ever be optimized for parallel execution where a single core processor may offer a price/performance benefit over a more costly multi core part that can't run that one task any faster.

Now, amiga users are fans of multitasking, after all it was always our OS's strength. Seems a bit daft to try to ignore the clear advantage of a multi core CPU in an SMP capable multitasking OS.

 be that as it may the fact is that today's OS's and more importantly most applications (afterall people care more about running apps not operating systems) don't take full advantage of multicore cpu's, its still an area that is evolving.

[stefcep2]

-edit-

Actually, looking back at it, I've been enjoying multicore computing ever since I got my first PPC board. A comparatively simple task (by current standards) such as playing back MP3, on the 68040 was a joke. It could manage mono 22kHz and there was no cpu time left to do anything else. That all changed when the PPC decoding engine was running in AmigaAMP. That whole arrangement was far less efficient than SMP (unavoidable considering they are two totally different processors) but the benefit of having a separate CPU core to dump the job onto was clear even then.

Gee that is really poor for a 68040.  I remember playing back mp3's in 14 bit 44 khz on a 40 Mhz  68040 Apollo A1200 (with executive) and it was fine (on a dblntsc screen).  I had a little shell script that opened up a requestor to select the mp3, beacsue from memory GUI-driven mp3 players seemed to significantly increase the cpu load when playing the same song.