2 CPU vs 1 CPU

[YedZed]

I have some questions about dual CPU systems. 

How would the performance of two quad core processors compare to one octo-core processor?

Do dual or quad CPU systems have scaling issues just like SLI and Crossfire? 

What are some known issues with multi-CPU systems? 

What impact does a multi-CPU system have on gaming and editing respectively?

Please tell me what you know or direct me to reading or video resources if you can. If you have first hand experiences, please share.

[alexhelvetica]

What CPUs are you comparing?

[tvolk131]

What is the workload you're optimizing this system for? And when you say an octa-core cpu, do you mean a true octa-core or a hyperthreaded quad core? For a gaming setup, fewer more powerful cores are much better so a single cpu is a much better idea, but for video editing, more cores makes a difference. If you're doing any gaming at all, go for a quad core desktop cpu.

[YedZed]

5 minutes ago, Comic_Sans_MS said:

What CPUs are you comparing?

Nothing in particular. This is mostly hypothetical. I was just looking at some old workstations, and deciding if they are worth my time.

[alexhelvetica]

2 minutes ago, YedZed said:

Nothing in particular. This is mostly hypothetical. I was just looking at some old workstations, and deciding if they are worth my time.

It depends. If you are comparing 2 CPUs of the same generation and clock-speed, they should preform very similarly if not the same, if you are comparing 2 older quadcore CPUs to a newer 8 core, the newer 8 core will win.

 

 

[glitchmaster0001]

3 minutes ago, YedZed said:

Nothing in particular. This is mostly hypothetical. I was just looking at some old workstations, and deciding if they are worth my time.

i made a dual hexa core system before for under $300 and the performance it packs for multithreaded stuff like rendering and workstation apps was just insane value for money. the gaming performance wasnt too bad considering what i paid to build the system but i know a quad core wouldve done better in gaming than 2 6 core 12 thread cpus. when i gamed only one of my 6 core cpus were used and the second one sat there doing nothing. though when i used OBS to do lossless recording while gaming that was when my second CPU was fully used and i didnt lose any FPS from lossless recording gameplay 

[YedZed]

Just now, Comic_Sans_MS said:

It depends. If you are comparing 2 CPUs of the same generation and clock-speed, they should preform very similarly if not the same, if you are comparing 2 older quadcore CPUs to a newer 8 core, the newer 8 core will win.

 

 

So to be sure, you are saying that 2 CPUs effectively function as one CPU? There's no advantage to either side? Would a dual CPU system see benefits in virtualization?

 

[YedZed]

12 minutes ago, tvolk131 said:

What is the workload you're optimizing this system for? And when you say an octa-core cpu, do you mean a true octa-core or a hyperthreaded quad core? For a gaming setup, fewer more powerful cores are much better so a single cpu is a much better idea, but for video editing, more cores makes a difference. If you're doing any gaming at all, go for a quad core desktop cpu.

Mostly hypothetical. See above.

[SpaceGhostC2C]

8 minutes ago, YedZed said:

I have some questions about dual CPU systems. 

How would the performance of two quad core processors compare to one octo-core processor?

Do dual or quad CPU systems have scaling issues just like SLI and Crossfire? 

What are some known issues with multi-CPU systems? 

What impact does a multi-CPU system have on gaming and editing respectively?

Please tell me what you know or direct me to reading or video resources if you can. If you have first hand experiences, please share.

I have worked with dual Xeons, but never in a gaming context, not I think it would be particularly easy as most all multi-socket motherboards are server oriented. having said that, you can always grab a server, install a game, and see what happens  Server motherboards are no a problem per se, but may lack software support for the chipset outside the server context or whatever. So it may work, but don't be surprised if the road isn't flat.

The other problem is that they hardly can host non-server CPUs, and server CPUs are heavily biased towards heavy multitasking and away from single/dual core performance.

 

Other things equal, that is, if you are choosing between slicing a CPU and plug each half to a different socket, or using the whole CPU in a single socket, no difference in total core count or type... Most likely one CPU solutions are better, but with a caveat. If you are running multiple tasks so independent of each other that you could run them in different computers, then there's no much point to either. But if you are running a scalable task like multithreaded programs or distributed computing, theoretically it depends on communication overheads and bottlenecks. Having two CPUs each with its own lanes to (different sets of) RAM, you reduce the bottleneck of multiple cores trying to communicate simultaneously with the memory. On the other hand, it increases the board size and makes communication between cores slower. I don't know enough to tell you how much core-to-core communication can actually take place. My experience with OpenMP and MPI in those Xeons biases me towards thinking that not much (since in both cases each core addresses RAM directly, and the whole output is just the implicit or explicit combination of their individual outputs as stored in memory).

Then again, could the CPU-RAm communication be more efficient by "pooling" small request to RAM made by cores within a CPU? Someone who knows way more than me should fill in there.

[alexhelvetica]

1 minute ago, YedZed said:

So to be sure, you are saying that 2 CPUs effectively function as one CPU? There's no advantage to either side? Would a dual CPU system see benefits in virtualization?

 

I have never messed around with dual CPU computers/servers before but I assume they will preform very similarly if not the same as an 8 core on the same generation and clockspeed, they may use more power though.

[YedZed]

2 minutes ago, SpaceGhostC2C said:

I have worked with dual Xeons, but never in a gaming context, not I think it would be particularly easy as most all multi-socket motherboards are server oriented. having said that, you can always grab a server, install a game, and see what happens  Server motherboards are no a problem per se, but may lack software support for the chipset outside the server context or whatever. So it may work, but don't be surprised if the road isn't flat.

The other problem is that they hardly can host non-server CPUs, and server CPUs are heavily biased towards heavy multitasking and away from single/dual core performance.

 

Other things equal, that is, if you are choosing between slicing a CPU and plug each half to a different socket, or using the whole CPU in a single socket, no difference in total core count or type... Most likely one CPU solutions are better, but with a caveat. If you are running multiple tasks so independent of each other that you could run them in different computers, then there's no much point to either. But if you are running a scalable task like multithreaded programs or distributed computing, theoretically it depends on communication overheads and bottlenecks. Having two CPUs each with its own lanes to (different sets of) RAM, you reduce the bottleneck of multiple cores trying to communicate simultaneously with the memory. On the other hand, it increases the board size and makes communication between cores slower. I don't know enough to tell you how much core-to-core communication can actually take place. My experience with OpenMP and MPI in those Xeons biases me towards thinking that not much (since in both cases each core addresses RAM directly, and the whole output is just the implicit or explicit combination of their individual outputs as stored in memory).

Then again, could the CPU-RAm communication be more efficient by "pooling" small request to RAM made by cores within a CPU? Someone who knows way more than me should fill in there.

I was looking at some old Dell Precision T*****s, which use dual Xeons. Either way it's better than my current specs.

[SpaceGhostC2C]

3 minutes ago, YedZed said:

I was looking at some old Dell Precision T*****s, which use dual Xeons. Either way it's better than my current specs.

How old? It will depend on what it has inside. If it helps as a reference, we had some rack-mounted Dells with dual Xeon E5540, 8 cores total each node, and no room for a discrete GPU. Today, each of those nodes performs worse than an FX-8xxx-based desktop in the same computational tasks, so they didn't age all that well. If cheap enough, they are still usable for parallel computing, but would not bet much on them for anything relying on strong, few cores.