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The Bulldozer Platform: Using FX-8150 To Test

AMD's Bulldozer Architecture: Overclocking Efficiency Explored
By , Achim Roos

Within the line-up of Zambezi chip, three models employ two Bulldozer modules totaling four cores, one includes three modules, adding up to six cores, and three are fully-featured four-module SKUs boasting eight cores. We're using the flagship FX-8150 for testing here. It's currently selling for about $270 bucks and, again, drops into the Socket AM3+ interface.

As you no doubt already know, AMD counts cores differently from Intel (or even from its previous architectures). In contrast to chip-level multiprocessing, where each core is complete and distinct, AMD uses the phrase chip-level multi-threading, and draws a distinction between modules and cores. The emphasis here is on efficiency in a multi-core design, positing that the days of single cores operating on their own are over. Rather than cramming in as many cores as possible onto a piece of silicon, brute-forcing the performance story, AMD tries to achieve an optimal balance by duplicating key resources, theoretically adding complexity where it'll be best utilized and avoiding waste in less sensitive parts of the chip.

Again, from our launch coverage of FX-8150:

...the Bulldozer module doesn’t incorporate two complete cores. Instead, it shares certain parts of what we’d expect to find as dedicated resources in a typical execution core, including instruction fetch and decode stages, floating-point units, and the L2 cache.

According to Mike Butler, chief architect behind Bulldozer, this is justifiable because traditional cores operating in a power-constrained environment don’t make optimal use of thermal headroom. That completely makes sense; when you’re trying to pack as many cores into a server as possible, you want to bias in favor of the resources most likely to be used most often, and avoid chewing up die space/power with components that can be shared without negatively impacting performance too severely.

...but simultaneously optimizing for performance and power necessitates sharing of certain resources.

The decision to share only bites you in the butt when both threads need the same resources, at which point performance drops relative to chip-level multiprocessing. But AMD is optimistic: last August, when it started releasing architectural details at the Hot Chips conference, it estimated that a Bulldozer module could average 80% of two complete cores, while only affecting die space minimally. As a result, in heavily-threaded environments, a Bulldozer-based processor should deliver significant efficiency improvements.

This also means AMD has to redefine what actually constitutes a core. To best accommodate its Bulldozer module, the company is saying that anything with its own integer execution pipelines qualifies as a core (no surprise there, right?), if only because most processor workloads emphasize integer math. I don’t personally have any problem with that definition. But if sharing resources negatively impacts per-cycle performance, then AMD necessarily has to lean on higher clocks or a greater emphasis on threading in order to compensate.

Learning To Share

Of course, AMD’s architects were careful in deciding which parts of the core could be shared, keeping power and efficiency in mind. As an example, following a branch misprediction, the front-end of a conventional core has to be flushed, wasting both bandwidth and power. Sharing that hardware between two cores helps improve the utilization of those resources. AMD also looked for areas where it could “afford” to share without hurting the timing of critical paths, hence the shared floating-point scheduler, which wasn’t considered to be as latency-sensitive as the integer units.

To the operating system, the resulting module appears as a pair of cores, similar to how a Hyper-Threaded core would appear. AMD is naturally eager to dispel the idea that Bulldozer will behave anything like Hyper-Threading (or SMT), claiming that its design facilitates better scalability than two threads sharing one physical core. Again, that makes sense—a Bulldozer module really can’t be characterized as a single core because many of its resources are, in fact, duplicated.

ModelBase Clock
Turbo-Core Clock
Max. Turbo Clock
TDPCoresTotal L2 CacheL3 CacheNorth Bridge Freq.
FX-81503.6 GHz3.9 GHz4.2 GHz125 W88 MB8 MB2.2 GHz
FX-81203.1 GHz3.4 GHz4.0 GHz125 / 95 W88 MB8 MB2.2 GHz
FX-81002.8 GHz3.1 GHz3.7 GHz95 W88 MB8 MB2.0 GHz
FX-61003.3 GHz3.6 GHz3.9 GHz95 W66 MB8 MB2.0 GHz
FX-41704.2 GHz-4.3 GHz125 W44 MB8 MB2.2 GHz
FX-B41503.8 GHz3.9 GHz4.0 GHz95 W44 MB8 MB2.2 GHz
FX-41003.6 GHz3.7 GHz3.8 GHz95 W44 MB8 MB2.0 GHz
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Top Comments
  • 32 Hide
    Darkerson , December 26, 2011 4:14 AM
    I know I have been critical in my comments here and there, but I really do hope Bulldozer helps AMD learn and refine Piledriver and future CPUs so that they are all better as a result. I know I will be skipping BD, but that doesnt mean I dont ever want to use AMD again. I will always root for the underdog, in hopes that we have another Athlon 64 on our hands again.
  • 30 Hide
    aznshinobi , December 26, 2011 3:47 AM
    Reading conclusion paragraph, I'd have to agree. I think they probably would've been better of using the STARS arch and just die shrinking it to 32nm.
  • 20 Hide
    Anonymous , December 26, 2011 8:20 AM
    Tom's Hardware finds that overclocking increases speed, power requirements. Film at 11.
Other Comments
  • 30 Hide
    aznshinobi , December 26, 2011 3:47 AM
    Reading conclusion paragraph, I'd have to agree. I think they probably would've been better of using the STARS arch and just die shrinking it to 32nm.
  • 32 Hide
    Darkerson , December 26, 2011 4:14 AM
    I know I have been critical in my comments here and there, but I really do hope Bulldozer helps AMD learn and refine Piledriver and future CPUs so that they are all better as a result. I know I will be skipping BD, but that doesnt mean I dont ever want to use AMD again. I will always root for the underdog, in hopes that we have another Athlon 64 on our hands again.
  • 5 Hide
    deadon2 , December 26, 2011 4:49 AM
    Fehh... did my build on a 990fx platform with a 955be CPU. Runs plenty fast, and I can upgrade the AM3+ in a year when AMD gets it right.

    Although I appreciate the work done on this article...

    Nothing to see here folks, move along...
  • 17 Hide
    dontcrosthestreams , December 26, 2011 5:34 AM
    im just fine with my 110$ 955be.... 29 deg idle at 3.7ghz
  • 4 Hide
    noob2222 , December 26, 2011 6:03 AM
    Is that a typo on page 7 and 8? "Clock Frequency: 4.5 GHz, Multiplier: 22.5x, CPU Voltage: 1.428 V" cpu-z shows 1.380? page 8 cpu z shows 1.44 and not 1.5.

    As for my own efficiency testing, I achieved 1.375V (cpu z), 4.4Ghz out of my 8120 with ease. I upped the NB to 1.115v (+.015V)wich added more stability and clocked the NB to 2600 to match HTT, wich brought another 1gb/s on sandra's memory test. All without disabling C1E or C3 states.

    Would be nice to see some followups with memory testing, BD responds to fast speeds. Hard to read since its in a different language but the graphs are easy enough to see
    http://www.planet3dnow.de/vbulletin/showthread.php?t=401023&garpg=13
  • 20 Hide
    Anonymous , December 26, 2011 8:20 AM
    Tom's Hardware finds that overclocking increases speed, power requirements. Film at 11.
  • -1 Hide
    de5_Roy , December 26, 2011 8:29 AM
    yay! another efficiency article from toms. :love: 
    sad to see amd's claims about efficiency turn out to be (much) less than accurate.
    some people are definitely gonna complain about the ram used (ddr3 1333) and windows 8 or lack of highly threaded benchmarks like truecrypt encryption or pov ray tracing (as if those are always used by regular users lol) and stuff.
    undervolting does look promising...but it doesn't seem to make any difference compared to sandy bridge systems. worse, bulldozer needs voltage increase to get more clockspeed.. i guess it will be more evident in fx 4100 and 6100 where substantial core voltage increase is necessary to get stock sandy bridge level performance out of them. that's just disappointing.
  • 3 Hide
    memadmax , December 26, 2011 9:51 AM
    It seems to me that Bulldozer is either a AMD bastard child chip, or it's a first gen chip of which subsequent generations of the architecture will be playing "catch up" performance wise. Otherwise, it's typical AMD trying to be efficient rather than a heavy hitter.

    But if you ask me, this is a "defensive" chip in the processor wars. And no war has been won playing defense.
  • -2 Hide
    de5_Roy , December 26, 2011 10:05 AM
    in any war, the best defense is a good offense. and amd has managed to offend most of the people who liked their cpus (fanboys excluded, obviously).
  • 9 Hide
    murambi , December 26, 2011 10:08 AM
    This article feels like when you are kicking a dog when its down. I really wanted AMD to challenge intel in the performance crown segment
  • 5 Hide
    salgado18 , December 26, 2011 10:22 AM
    pafnucyTom's Hardware finds that overclocking increases speed, power requirements. Film at 11.

    Conclusion is stupid, but the tests are relevant. Nice article.
  • 6 Hide
    technoholic , December 26, 2011 10:38 AM
    My latest decision about BD is that it is not a matured product YET. No, the war isnt lost, only 1 or 2 fronts are lost and that doesnt mean the war is lost. The ultimate problem of this chip is that it needs much power to operate. I am not a tech geek or a pro in CPU architecture but i think that AMD needs to do some improvements in the architecture, too (also in software side)

    Maybe some people will criticize me for this but i always like the most updated/newest approaches in tech; not the older and faster. But newer approaches mostly suffer from immature designs. However, i believe we will see some excellent CPUs from AMD in the near future. Because at least the idea behind this architecture is not worse than that of phenoms. Let's not forget, giant firms like Intel also had many failures in their history (remember pentium 3 was a mediocre design and 4 was much worse), but they managed to advance further with their new ideas. I am sure in this moment AMD guys are working hard on their next big step.
  • -2 Hide
    g4114rd0 , December 26, 2011 10:54 AM
    Start and end each attack and defence pattern with a poise pattern,
    such as Single Scorpius emerges from Cave,
    which can also be use for attack or defence.
  • -7 Hide
    theuniquegamer , December 26, 2011 10:58 AM
    Its true that amd's stock coolers are not efficient as the intel's . Because i have both intel i5 760k and amd 955be system , the amd system runs so loud at 40c on stock settings (idle) and the intel runs at above 57c on stock (idle). It makes noise after 70c.(I am not comparing intel with amd because intel i5 is 32nm amd 955 is 45nm). So i think amd should provide good quality stock coolers in the black edition cpus. I
  • 6 Hide
    zooted , December 26, 2011 11:03 AM
    ^Amd's stock coolers are better.
  • -6 Hide
    Anonymous , December 26, 2011 11:31 AM
    Did AMD specifically ask Tom's and Anand to show their CPUs on the front page covered with thermal paste and generally looking dirty and unattractive, or did Intel specifically request it? I have a hard time believing that both of you came up with the same stupid idea.

    In other news, your desktop PC has relatively low power requirements compared to every other appliance in you house, if you think you need to worry about a lousy few watts, you'd probably be better off switching to more efficient light bulbs and finding a lower wattage coffee pot first.
  • -6 Hide
    elbert , December 26, 2011 11:59 AM
    I stopped reading when I seen 1333 memory. If you don't show Overclocked memory past 1866 I don't want to waste my time.
  • 1 Hide
    Yuka , December 26, 2011 12:12 PM
    200.7Mhz HT Link?

    I almost stopped reading there, but I remembered it was an efficiency run.

    It's nice too see they suffer from the same problem the Phenoms do. AMD over estimates voltage with their CPUs, so at default-everything it's going to be more power hungry. With a nice tunning, they can run as cool as their Intel counterparts (cool, but not as fast, sadly).

    Good to see they also over estimated stock voltages for the FX line; gives me hope for low power CPUs.

    Cheers!
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