Core i7 and chess

[bob]

I am not sure how your test works but it would probably not be an accurate estimation of hardware for Rybka. Rybka 3 on Octa 4Ghz will be stronger than a Core i7 4Ghz by about 30%. Also if you are using a Core i7 with Rybka 3, you should turn off hyperthreading, otherwise you get a 20% to 30% hit in performance. I find it interesting that somehow Toga seems to do better with hyperthreading turned on ... maybe Rybka 3 needs a recompile?

No, Toga needs some tuning to eliminate some of the memory contention (cache misses) that it suffers from. Once you get this tuned, hyper-threading will no longer help. I went thru this when hyper-threading first came out. It initially helped Crafty, but today hurts badly.

[Gian-Carlo Pascutto]

I don't see any problem,because the chess engine should see the 8threads and use them like 8cores..and if you turn HT off then is it just a quad core cpu! So,i think the problem must be in Rybka! and i'am sure the core i7 is faster then a skulltrail for chess!
I have used Toga ,because i have to use freeware,i even could use Glaurung or a other strong engine..but it was not easy to let people run a chess program..(they think it's a benchmark program like pi or something)
and that take not long time,not to have settings,just let it run from start position and infinite level.I have a few people who find it very interesting and also find out that they can fine tune there system! (better then Prime)
I have almost all my parts to build my own core i7 system,then i can try all my engines to see if they act the same,and logic they should run faster with HT on(8threads)!

JP.

You are completely wrong!

The problem is not with Rybka. Hyperthreaded CPU's are NOT REAL CPUS. The problem is that hyperthreading gives (for example) a 30% boost in NPS, but the efficiency of the engine drops much more significantly because the parallelism is not so efficient on 8 CPUs as it is on 4.

When Rybka displays the NPS on a multiprocessor machine, IT FACTORS IN THE PARALLEL EFFICIENCY. This is why it drops with hyperthreading enabled: the extra speed is simply not compensating for the loss in efficiency.

Other programs just display the real NPS. So they get more NPS with hyperthreading, but this doesn't mean they will actually be faster!

[zullil]

I am still trying to understand this topic. What, if anything, should I infer by comparing lines 1 and 5 in the following table (copied from http://www.sedatchess.com/craftybenchmarks.html )?

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------------------------------------------------------------------------------------------- 
Program        Exe      Processor       GHz     Threads   Kn/s       Time    Hardware User 
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Crafty v22.8   64 bit   i7 920 HT off  @4.00GHz   4CPU    18072085   8.27    Phil Harris 
Crafty v22.8   64 bit   2x QX9775      @4.00GHz   8CPU    21239451   9.34    Lukas Cimiotti 
Crafty v22.8   64 bit   i7 920 HT off  @3.80GHz   4CPU    16811057   9.63    Lukas Cimiotti 
Crafty v22.8   64 bit   Intel QX9650   @3.81GHz   4CPU    15404968   10.22   Sedat Canbaz 
Crafty v22.8   64 bit   i7 920 HT on   @4.00GHz   8CPU    18708859   12.17   Phil Harris 
Crafty v22.8   64 bit   Intel QX6700    2.66GHz   4CPU    11000419   14.52   Sedat Canbaz 
Crafty v22.8   64 bit   AMD X2 4600+    2.40GHz   2CPU    4084622    31.83   Sedat Canbaz 
Crafty v22.8   32 bit   AMD Turion Mob. 2.20GHz   2CPU    2286735    57.21   Sedat Canbaz 
Crafty v22.8   32 bit   AMD 64 3400+    2.40GHz   1CPU    1431694    78.64   Sedat Canbaz 
Crafty v22.8   32 bit   Pentium 4       3.20GHz   1CPU    839640     133.05  Levent Kaya
Crafty v22.8   32 bit   Intel Celeron   1.70GHz   1CPU    423000     264.25  Sedat Canbaz 
-------------------------------------------------------------------------------------------

[Sean Evans]

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------------------------------------------------------------------------------------------- 
Program        Exe      Processor       GHz     Threads   Kn/s       Time    Hardware User 
------------------------------------------------------------------------------------------- 
Crafty v22.8   64 bit   i7 920 HT off  @4.00GHz   4CPU    18072085   8.27    Phil Harris 
 
Crafty v22.8   64 bit   i7 920 HT on   @4.00GHz   8CPU    18708859   12.17   Phil Harris 
-------------------------------------------------------------------------------------------

These two seem to state HT would be better left on!

Sean

[Gian-Carlo Pascutto]

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------------------------------------------------------------------------------------------- 
Program        Exe      Processor       GHz     Threads   Kn/s       Time    Hardware User 
------------------------------------------------------------------------------------------- 
Crafty v22.8   64 bit   i7 920 HT off  @4.00GHz   4CPU    18072085   8.27    Phil Harris 
 
Crafty v22.8   64 bit   i7 920 HT on   @4.00GHz   8CPU    18708859   12.17   Phil Harris 
-------------------------------------------------------------------------------------------

These two seem to state HT would be better left on!

Sean

No they dont. I don't know where you get that. There is a measly increase in NPS for a gargantuan loss in parallel efficiency. A clear losing situation.

[jpqy]

Here i see my PC q6600 g0 @3.2Ghz and the core i7 @2.93Ghz(stock) with HT off has almost the same nodes..to get Depth 21 need 5m12s and 4m47s

Then core i7 HT on @3.2Ghz he get 2Milj.nodes more and Depth 21 in 3m08 i win 2min. in time!

71) TogaII141SE-4cpu 21/52 05:12 364.182.100 4.576.252 +0,20 Q6600 g0 @ 3.2Ghz (My PC)
72) TogaII142JD-4cpu 21/50 04:47 164.070.553 4.562.555 +0.24 Nehalem @2.93Ghz HT off (cpu 50%)
TogaII142JD-8cpu 21/46 03:08 151.186.585 6.411.283 +0,24 Nehalem @3.2Ghz

A Step Higher..Skulltrail @4Ghz 6.2Milj nodes D21 in 3m31s
Core i7 HT on @4Ghz...8.5Milj nodes..D21 in 2m02s!! win again 1m29s!

TogaII142JD-8cpu 21/44 02:02 132.792.624 8.563.902 +0.19 Core i7 920 @4.10Ghz
TogaII142JD-8cpu 21/52 03:31 174.872.390 6.286.188 +0.25 Skulltrail 2xQX9775 @ 4.0Ghz

I think i know what my next cpu will be!!
Wrong or not wrong.These are just examples from more then 100 tests results i get!

JP.

[terminator]

Mind my language but the Core i7 seems to kick @ss from what I've seen.

[zullil]

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------------------------------------------------------------------------------------------- 
Program        Exe      Processor       GHz     Threads   Kn/s       Time    Hardware User 
------------------------------------------------------------------------------------------- 
Crafty v22.8   64 bit   i7 920 HT off  @4.00GHz   4CPU    18072085   8.27    Phil Harris 
 
Crafty v22.8   64 bit   i7 920 HT on   @4.00GHz   8CPU    18708859   12.17   Phil Harris 
-------------------------------------------------------------------------------------------

These two seem to state HT would be better left on!

Sean

No they dont. I don't know where you get that. There is a measly increase in NPS for a gargantuan loss in parallel efficiency. A clear losing situation.

The search rates in NPS are essentially equal, but with HT enabled the search time is roughly 50% more. So with HT enabled, the search hits about 50% more nodes? Why is this bad (or inefficient)? Forgive me, I'm still confused. Please help me grasp this!

[Mark]

Kind of an aside here, but does a standard Q6600 have hyperthreading? If so, I'd like to be able to turn it off... Thanks!

[terminator]

Kind of an aside here, but does a standard Q6600 have hyperthreading? If so, I'd like to be able to turn it off... Thanks!

Unless you can back it up with a link, I believe hyperthreading is not present in (earlier) Quads and Dual Cores. It has resurfaced in the Core i7 (dubbed Intel Core 3).