8x or 2x4x Computer: Best v Cheapest for Chess

[beachknight]

Subject: Which octal should I buy?

Dear members,

For the past two weeks, I have been investigating an octal which suits
best for my chess needs.

Here in Antalya, I could find only one box with a great cooling fan to
my surprise.

Main proc: i7 920
OS : 64 bit W7, but could not see which one?

I have run fritz benchmark

[Fritz Chess Benchmark.exe, 452 KB (462.848 bytes), 06.11.2005]

and

Crafty-1920-smp.exe, 960 KB (983.040 bytes), 24.08.2005, Dann's compile]

on the box.

Results:

Fritz on 8cpu: around 20
Fritz on 4cpu: around 16

Crafty on 4cpu: around 9 mNpS time elapsed: dont remember
Crafty on 8cpu: around 7 mNpS time elapsed: bigger than above

I have expected around 30 (F) and 20+ (C) on 8cpu, resp.

There is a problem like the one Clemens described some time ago?

Thoughts?

[lmader]

The Intel i7 920 isn't an 8 core machine - it's a 4 core machine with hyperthreading. Hyperthreading simulates an extra core for each of the actual physical cores, but these are not "true" additional cores. Internally the chip is designed to have extra CPU resources that allow part of a "real" core to continue working on one thread while another part of the same "real" core is working on another thread. Thus one core can execute two threads simultaneously, but only for very limited parts of the execution.

For some applications this provides a real increase in speed - unfortunately for chess engines it never pays off. The reason that hyperthreading doesn't help for chess engines has to do with the way the parallel algorithms for searching the tree work - each thread generally has to have its own part of the search tree to work on, but there is always redundancy in the way the search tree is spread across the threads. The search tree for each thread isn't purely discreet, each thread has duplicate parts of the tree. Thus the total aggregate size of the search tree gets bigger and bigger as you add more threads to the search.

So although you do see a small increase in the number of nodes/sec with hyperthreading, the total number of nodes that must be searched is actually greater than the small speedup afforded by hyperthreading - because the total size of the tree gets larger as it is spread across the threads.

This is why you see only a modest increase in the speed going from the 4 "real" cores to the 4 real cores + 4 hyperthreaded cores - you aren't actually adding real cores, your adding weak hyperthreaded cores. And this increase in nodes/sec is misleading because despite the extra speed you aren't actually searching deeper - you're searching a much larger tree such that you don't realize that payoff.

So, the point is that where chess engine performance is concerned, you won't realize any benefit from those hyperthreaded "cores". For all intents and purposes, in the chess engine world, consider it a 4 core machine.

[beachknight]

Thanks, Lar for the clearing the issue. The question is now transformed
into: which octals I should consider?

They say some parts are not available in market in Antalya and in Turkey.

TIA,

[lmader]

Ahh, I see.

I am not aware of any 8 core CPUs that are available at this time. I think that Intel is just now releasing a 6 core CPU, and AMD has a 6 core CPU coming soon as well.

You can get dual quad core machines though, but I think these have to be Xeon processors, which are pretty expensive.

[Hugo]

Hello Harun,

for what do you need a machine with 8 real cpu cores?
Only a few engines get a measureable plus from 4 upto 8 cpus.
I did many longtime tests in the past.
Zappa, DeepFritz 11 showed an improovment on 8 cores. The rest of top ten was average.

Regards, clemens

[Dr.Wael Deeb]

Hello Harun,

for what do you need a machine with 8 real cpu cores?
Only a few engines get a measureable plus from 4 upto 8 cpus.
I did many longtime tests in the past.
Zappa, DeepFritz 11 showed an improovment on 8 cores. The rest of top ten was average.

Regards, clemens

I do agree here,it's not worth it and besides,a newer generations are just around the corner and they'll definitely worth their bucks....
Dr.D

[michiguel]

Hello Harun,

for what do you need a machine with 8 real cpu cores?
Only a few engines get a measureable plus from 4 upto 8 cpus.
I did many longtime tests in the past.
Zappa, DeepFritz 11 showed an improovment on 8 cores. The rest of top ten was average.

Regards, clemens

For testing, an octa is exactly twice as better than a quad

With an octa, you can test engines at full potential (using four cores) with pondering "on"

Miguel

[lmader]

And besides, more is always better.

[beachknight]

Ahh, I see.

I am not aware of any 8 core CPUs that are available at this time. I think that Intel is just now releasing a 6 core CPU, and AMD has a 6 core CPU coming soon as well.

You can get dual quad core machines though, but I think these have to be Xeon processors, which are pretty expensive.

Yep, prices of Xeons are some 20k, I have found.
They are out of budget, I am afraid.

Any pre-tests on these new 6 core procs?

PS: Should have bought this months pc magazine

[M ANSARI]

You could probably get a dual Xeon 9775 and run it on a Skulltrail pretty cheap on ebay. Most people I know that have that setup can easily run 8 cores at 4 Ghz. On the other hand a highly overclocked i920 or its Xeon equivalent can also reach 4 Ghz or more on water and will give the 8 core system a run for its money. While not as strong as the 8 core with 4 cores, maybe with 6 cores it will be. I would wait for the 6 core i920 or xeon equivalent and push those 6 cores to the max. I think a non overclocked Nehalem 8 core will have trouble keeping up and since an overclockable platform for the dual socket Nehalem doesn't look like it will happen, the highest performing chess hardware might just be a overclocked 6 core i series setup.