Intel's Pentium Extreme Edition 955: 65nm, 4 threads and 376M transistors
by Anand Lal Shimpi on December 30, 2005 11:36 AM EST- Posted in
- CPUs
Literally Dual Core
One of the major changes with Presler is that unlike Smithfield, the two cores are not a part of the same piece of silicon. Instead, you actually have a single chip with two separate die on it. By splitting the die in two, Intel can reduce total failure rates and even be far more flexible with their manufacturing (since one Presler chip is nothing more than two Cedar Mill cores on a single package).
In order to find out if there was an appreciable increase in core-to-core communication latency, we used a tool called Cache2Cache, which Johan first used in his series on multi-core processors. Johan's description of the utility follows:
Not only did we not find an increase in latency between the two cores on Presler, communication actually occurs faster than on Smithfield. We made sure that it had nothing to do with the faster FSB by clocking the chip at 2.8GHz with an 800MHz FSB and repeated the tests only to find consistent results.
We're not sure why, but core-to-core communication is faster on Presler than on Smithfield. That being said, a difference of less than 9ns just isn't going to be noticeable in the real world - given that we've already seen that the Athlon 64 X2's 100ns latency doesn't really help it scale better when going from one to two cores.
One of the major changes with Presler is that unlike Smithfield, the two cores are not a part of the same piece of silicon. Instead, you actually have a single chip with two separate die on it. By splitting the die in two, Intel can reduce total failure rates and even be far more flexible with their manufacturing (since one Presler chip is nothing more than two Cedar Mill cores on a single package).
The chip at the bottom of the image is Presler; note the two individual cores.
In order to find out if there was an appreciable increase in core-to-core communication latency, we used a tool called Cache2Cache, which Johan first used in his series on multi-core processors. Johan's description of the utility follows:
"Michael S. started this extremely interesting thread at the Ace's hardware Technical forum. The result was a little program coded by Michael S. himself, which could measure the latency of cache-to-cache data transfer between two cores or CPUs. In his own words: "it is a tool for comparison of the relative merits of different dual-cores."Armed with Cache2Cache, we looked at the added latency seen by Presler over Smithfield:
"Cache2Cache measures the propagation time from a store by one processor to a load by the other processor. The results that we publish are approximately twice the propagation time. For those interested, the source code is available here."
| Cache2Cache Latency in ns (Lower is Better) | |
| AMD Athlon 64 X2 4800+ | 101 |
| Intel Smithfield 2.8GHz | 253.1 |
| Intel Presler 2.8GHz | 244.2 |
Not only did we not find an increase in latency between the two cores on Presler, communication actually occurs faster than on Smithfield. We made sure that it had nothing to do with the faster FSB by clocking the chip at 2.8GHz with an 800MHz FSB and repeated the tests only to find consistent results.
We're not sure why, but core-to-core communication is faster on Presler than on Smithfield. That being said, a difference of less than 9ns just isn't going to be noticeable in the real world - given that we've already seen that the Athlon 64 X2's 100ns latency doesn't really help it scale better when going from one to two cores.
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Betwon - Saturday, December 31, 2005 - link
NO, 2. is wrong.We need to know the end time of all tasks.
The sum of each task's time will mislead.
Because it can not show the real time spend to complete those tasks. (Time is overlayed)
Viditor - Saturday, December 31, 2005 - link
That's what I thought you meant...it's not misleading to me (nor to most of the other readers I gather, since nobody else has come forward). If you want to know the time to complete all tasks, then just take the largest time number of what ever test you wish.
The reason that the setup they used appeals to me is that it helps me understand how an individual application is affected under those conditions, and the totals give me a relative picture of each of the apps as a whole. They haven't said that the time listed in the "Total" is actually how long things took in reality, they said it was the total of the times.
I understand that the difference in those two phrases is perhaps a difficulty that many have when understanding a foriegn language...
In the future, you might want to be less confrontational about your questions...
Phrases like "There are still many knowledge about CPU that anandtech need to learn" are considered quite inhospitable...
fitten - Saturday, December 31, 2005 - link
No. What is being mentioned here is "Wall Clock Time" vs. summation of execution times. You start a stopwatch at the instant you start your task bundle and when the last task in the bundle is finished, you stop your stopwatch. That's the wall clock time. Measuring CPU utilization time is quite easily seen to be false. with two CPUs, two tasks may take 20s each to finish, but they may start and finish at the same time after 20s of wall clock time... not 20s + 20s = 40s (each task will see 20s of CPU utilization time, but those sets of 20s are simultaneously used... 20s on one CPU and 20s on the other CPU at the same time - for a wall clock finish time of 20s, not 40s).And, you cannot simply take the largest time number. For example, suppose a task that runs for 1s is blocked by a second task which takes 10s, then the first task takes another 1s to finish, while 10s is larger than 2s, the wall clock time for this bundle is actually 12s (1s + 10s + 1s), not 10s or 2s.
bldckstark - Monday, January 2, 2006 - link
Ummmmm, all of the times you are screaming about are listed. You can work it out for yourself. Although, when you look at the concurrent timing for each app, you will find that the AMD posted a better score. Concurrent timing results -AMD 4800+ - 65.9s
955EE No HT - 83.3
955EE With HT - 71.1
Consecutive times of course show a different picture, and most of all, SPCC is a wreck during all of this for AMD.
I have to say, I can't remember when I last opened 4 huge memory and CPU hogging programs at exactly the same time that I tried to play a game. These CPU's may be great at doing this many activities at once, but I can only do one thing at a time. Each of these programs would be started separately, and when they are on their way, I might start gaming. This is a great test, but not realistic.
Betwon - Friday, December 30, 2005 - link
Your test of the SMP game --Quake4Your result is diffirent with the result of the more detail test from FiringSquad.
http://www.firingsquad.com/hardware/quake_4_dual-c...">http://www.firingsquad.com/hardware/qua...-core_pe...
We find that both HT and multi-core will improve the fps. P4 540 HT is about 1x % improvement.
We need your explains. Why you say that HT will not help the in the the SMP game --Quake4?
And we do not find that AthlonX2 have the more excellent improvement than PD, when they work (change from single-core-work to multi-core-work).
Where is the benefits of on-die communication? 101ns latency? why is it slower the lateny of the memory? Is your cache2cache test software wrong?
The test shows that
SMPon/SMPoff PD840 102.9 fps/74.8 fps --> 37.6% improvement
SMPon/SMPoff X2 3800+ 101.1 fps/74.4 fps --> 35.9% improvement
SMPon/SMPoff X2 4800+ 103.2 fps/87.7 fps --> 17.7% improvement
AMD test:
http://www.firingsquad.com/hardware/quake_4_dual-c...">http://www.firingsquad.com/hardware/qua...al-core_...
Intel test:
http://www.firingsquad.com/hardware/quake_4_dual-c...">http://www.firingsquad.com/hardware/qua...-core_pe...
The improvement ratio of PD is better than that of athlonX2.
psychobriggsy - Saturday, December 31, 2005 - link
> SMPon/SMPoff PD840 102.9 fps/74.8 fps --> 37.6% improvement> SMPon/SMPoff X2 3800+ 101.1 fps/74.4 fps --> 35.9% improvement
> SMPon/SMPoff X2 4800+ 103.2 fps/87.7 fps --> 17.7% improvement
Looks like the issue is an upper performance limit around the 103 fps mark that probably isn't caused by the CPU - e.g., GPU or something else.
If it is a memory bandwidth issue (which should be easy to test for by using faster memory and running the tests again) then there isn't much that can be done. Then again, the Intel processor uses DDR2 so ...
If the 4800+ improved by 36% like the 3800+ then it would achieve around 120fps.
In the end it just shows that the lower-priced dual-cores are still a better deal ... especially as they can be overclocked quite nicely.
Viditor - Friday, December 30, 2005 - link
I would hope so, since the patch was partially written by Intel...
http://firingsquad.com/hardware/quake_4_dual-core_...">http://firingsquad.com/hardware/quake_4_dual-core_...
Betwon - Saturday, December 31, 2005 - link
PD840 139.1fps/83fps --> 67.6%PD840 are 67.6 percent faster at 800x600 with threading enabled.
67.6% > 63%
Patch was partially written by Intel...?
But the patch is very excellent!
This patch is the most improvement game patch for SMP CPU.
We can not find that another SMP game patch can improvement the game performent so much.
Good quality of the codes!
Betwon - Saturday, December 31, 2005 - link
PD840 139.1fps/83fps --> 67.6%PD840 are 67.6 percent faster at 800x600 with threading enabled.
67.6% > 63%
Patch was partially written by Intel...?
But the patch is very excellent!
This patch is the most improvement game patch for SMP CPU.
We can not find that another SMP game patch can improvement the game performent so much.
Good quality of the codes!
Viditor - Saturday, December 31, 2005 - link
Possibly, but Intel is well known for creating an imbalance in performance for their processors using software (e.g. the Intel Compiler). Most likely, future versions of the patch will correct for this. Either way, it really says less about the CPU than it does the patch...