Quick Take: Magny-Cours Spotted, Pushed to 3GHz for wPrime

September 13, 2009

Andreas Galistel at NordicHardware posted an article showing a system running a pair of engineering samples of the Magny-Cours processor running at 3.0GHz. Undoubtedly these images were culled from a report “leaked” on XtremeSystems forums showing a “DINAR2” motherboard with SR5690 chipset – in single and dual processor installation – running Magny-Cours at the more typical pre-release speed of 1.7GHz.

We know that Magny-Cours is essentially a MCM of Istanbul delivered in the rectangular socket G34 package. One thing illuminating about the two posts is the reported “reduction” in L3 cache from 12MB (6MB x 2 in MCM) to 10MB (2 x 5MB in MCM). Where did the additional cache go? That ‘s easy: since a 2P Magny-Cours installation is essentially a 4P Istanbul configuration, these processors have the new HT Assist feature enabled – giving 1MB of cache from each chip in the MCM to HT Assist.

“wPrime uses a recursive call of Newton’s method for estimating functions, with f(x)=x2-k, where k is the number we’re sqrting, until Sgn(f(x)/f'(x)) does not equal that of the previous iteration, starting with an estimation of k/2. It then uses an iterative calling of the estimation method a set amount of times to increase the accuracy of the results. It then confirms that n(k)2=k to ensure the calculation was correct. It repeats this for all numbers from 1 to the requested maximum.”

wPrime site

Another thing intriguing about the XtremeSystems post in particular is the reported wPrime 32M and 1024M completion times. Compared to the hyper-threading-enabled 2P Xeon W5590 (130W TDP) running wPrime 32M at 3.33GHz (3.6GHz turbo)  in 3.950 seconds, the 2P 3.0GHz Magny-Cours completed wPrime 32M in an unofficial 3.539 seconds – about 10% quicker while running a 10% slower clock. From the myopic lens of this result, it would appear AMD’s choice of “real cores” versus hyper-threading delivers its punch.

SOLORI’s Take: As a “reality check” we can compared the reigning quad-socked, quad-core Opteron 8393 SE result in wPrime 32M and wPrime 1024M at 3.90 and 89.52  seconds, respectively. Adjusted for clock and core count versus its Shanghai cousin, the Magny-Cours engineering samples – at 3.54 and 75.77 seconds, respectively – turned-in times about 10% slower than our calculus predicted. While still “record breaking” for 2P systems, we expected the Magny-Cours/Istanbul cores to out-perform Shanghai clock-per-clock – even at this stage of the game.

Due to the multi-threaded nature of the wPrime benchmark, it is likely that the HT Assist feature – enabled in a 2P Magny-Cours system by default – is the cause of the discrepancy. By reducing the available L3 cache by 1MB per die – 4MB of L3 cache total – HT Assist actually could be creating a slow-down. However, there are several things to remember here:

  • These are engineering samples qualified for 1.7GHz operation
  • Speed enhancements were performed with tools not yet adapted to Magny-Cours
  • The author indicated a lack of control over AMD’s Cool ‘n Quiet technology which could have made “as tested” core clocks somewhat lower than what CPUz reported (at least during the extended tests)
  • It is speculated that AMD will release Magny-Cours at 2.2GHz (top bin) upon release, making the 2.6+ GHz results non-typical
  • The BIOS and related dependencies are likely still being “baked”

Looking at the more “typical” engineering sample speed tests posted on the XtremeSystems’ forum tracks with the 3.0GHz overclock results at a more “typical” clock speed of 2.6GHz for 2P Magny-Cours: 3.947 seconds and 79.625 seconds for wPrime 32M and 1024M, respectively. Even at that speed, the 24-core system is on par with the 2P Nehalem system clocked nearly a GHz faster. Oddly, Intel reports the W5590  as not supporting “turbo” or hyper-threading although it is clear that Intel’s marketing is incorrect based on actual testing.

Assuming Magny-Cours improves slightly on its way to market, we already know how 24-core Istanbul stacks-up against 16-thread Nehalem in VMmark and what that means for Nehalem-EP. This partly explains the marketing shift as Intel tries to position Nehalep-EP as a destined for workstations instead of servers. Whether or not you consider this move a prelude to the ensuing Nehalem-EX v. Magny-Cours combat to come or an attempt to keep Intel’s server chip power average down by eliminating the 130W+ parts from the “server” list,  Intel and AMD will each attempt win the war before the first shot is fired. Either way, we see nothing that disrupts the price-performance and power-performance comparison models that dominate the server markets.

[Ed: The 10% difference is likely due to the fact that the author was unable to get “more than one core” clocked at 3.0GHz. Likewise, he was uncertain that all cores were reliably clocking at 2.6GHz for the longer wPrime tests. Again, this engineering sample was designed to run at 1.7GHz and was not likely “hand picked” to run at much higher clocks. He speculated that some form of dynamic core clocking linked to temperature was affecting clock stability – perhaps due to some AMD-P tweaks in Magny-Cours.]

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