• What
    is this?
    You've landed on the AMD Portal on AnandTech. This section is sponsored by AMD. It features a collection of all of our independent AMD content, as well as Tweets & News from AMD directly. AMD will also be running a couple of huge giveaways here so check back for those.
    PRESENTED BY

Power Management and Real Turbo Core

Like Llano, Bulldozer incorporates significant clock and power gating throughout its design. Power gating allows individual idle cores to be almost completely powered down, opening up headroom for active cores to be throttled up above and beyond their base operating frequency. Intel's calls this dynamic clock speed adjustment Turbo Boost, while AMD refers to it as Turbo Core.

The Phenom II X6 featured a rudimentary version of Turbo Core without any power gating. As a result, Turbo Core was hardly active in those processors and when it was on, it didn't stay active for very long at all.

Bulldozer's Turbo Core is far more robust. While it still uses Llano's digital estimation method of determining power consumption (e.g. the CPU knows ALU operation x consumes y-watts of power), the results should be far more tangible than what we've seen from any high-end AMD processor in the past.

Turbo Core's granularity hasn't changed with the move to Bulldozer however. If half (or fewer) of the processor cores are active, max turbo is allowed. If any more cores are active, a lower turbo frequency can be selected. Those are the only two frequencies available above the base frequency.

AMD doesn't currently have a Turbo Core monitoring utility so we turned to Core Temp to record CPU frequency while running various workloads to measure the impact of Turbo Core on Bulldozer compared to Phenom II X6 and Sandy Bridge.

First let's pick a heavily threaded workload: our x264 HD benchmark. Each run of our x264 test is composed of two passes: a lightly threaded first pass that analyzes the video, and a heavily threaded second pass that performs the actual encode. Our test runs four times before outputting a result. I measured the frequency of Core 0 over the duration of the test.

Let's start with the Phenom II X6 1100T. By default the 1100T should run at 3.3GHz, but with half or fewer cores enabled it can turbo up to 3.7GHz. If Turbo Core is able to work, I'd expect to see some jumps up to 3.7GHz during the lightly threaded passes of our x264 test:

Unfortunately we see nothing of the sort. Turbo Core is pretty much non-functional on the Phenom II X6, at least running this workload. Average clock speed is a meager 3.31GHz, just barely above stock and likely only due to ASUS being aggressive with its clocking.

Now let's look at the FX-8150 with Turbo Core. The base clock here is 3.6GHz, max turbo is 4.2GHz and the intermediate turbo is 3.9GHz:

Ah that's more like it. While the average is only 3.69GHz (+2.5% over stock), we're actually seeing some movement here. This workload in particular is hard on any processor as you'll see from Intel's 2500K below:

The 2500K runs at 3.3GHz by default, but thanks to turbo it averages 3.41GHz for the duration of this test. We even see a couple of jumps to 3.5 and 3.6GHz. Intel's turbo is a bit more consistent than AMD's, but average clock increase is quite similar at 3%.

Now let's look at the best case scenario for turbo: a heavy single threaded application. A single demanding application, even for a brief period of time, is really where these turbo modes can truly shine. Turbo helps launch applications quicker, make windows appear faster and make an easy time of churning through bursty workloads.

We turn to our usual favorite Cinebench 11.5, as it has an excellent single-threaded benchmark built in. Once again we start with the Phenom II X6 1100T:

Turbo Core actually works on the Phenom II X6, albeit for a very short duration. We see a couple of blips up to 3.7GHz but the rest of the time the chip remains at 3.3GHz. Average clock speed is once again, 3.31GHz.

Bulldozer does far better:

Here we see blips up to 4.2GHz and pretty consistent performance at 3.9GHz, exactly what you'd expect. Average clock speed is 3.93GHz, a full 9% above the 3.6GHz base clock of the FX-8150.

Intel's turbo fluctuates much more frequently here, moving between 3.4GHz and 3.6GHz as it runs into TDP limits. The average clock speed remains at 3.5GHz, or a 6% increase over the base. For the first time ever, AMD actually does a better job at scaling frequency via turbo than Intel. While I would like to see more granular turbo options, it's clear that Turbo Core is a real feature in Bulldozer and not the half-hearted attempt we got with Phenom II X6. I measured the performance gains due to Turbo Core across a number of our benchmarks:

Average performance increased by just under 5% across our tests. It's nothing earth shattering, but it's a start. Don't forget how unassuming the first implementations of Turbo Boost were on Intel architectures. I do hope with future generations we may see even more significant gains from Turbo Core on Bulldozer derivatives.

Independent Clock Frequencies

When AMD introduced the original Phenom processor it promised more energy efficient execution by being able to clock each core independently. You could have a heavy workload running on Core 0 at 2.6GHz, while Core 3 ran a lighter thread at 1.6GHz. In practice, we felt Phenom's asynchronous clocking was a burden as the CPU/OS scheduler combination would sometimes take too long to ramp up a core to a higher frequency when needed. The result, at least back then, was that you'd get significantly lower performance in these workloads that shuffled threads from one core to the next. The problem was so bad that AMD abandoned asynchronous clocking altogether in Phenom II.

The feature is back in Bulldozer, and this time AMD believes it will be problem free. The first major change is with Windows 7, core parking should keep some threads from haphazardly dancing around all available cores. The second change is that Bulldozer can ramp frequencies up and down much quicker than the original Phenom ever could. Chalk that up to a side benefit of Turbo Core being a major part of the architecture this time around.

Asynchronous clocking in Bulldozer hasn't proven to be a burden in any of our tests thus far, however I'm reluctant to embrace it as an advantage just yet. At least not until we've had some more experience with the feature under our belts.

The Pursuit of Clock Speed The Impact of Bulldozer's Pipeline
POST A COMMENT

428 Comments

View All Comments

  • Kristian Vättö - Wednesday, October 12, 2011 - link

    I'm happy that I went with i5-2500K. Performance, especially in gaming, seems to be pretty horrible. Reply
  • ckryan - Wednesday, October 12, 2011 - link

    I was just going to say the same thing. I was all about AMD last year, but early this year I picked up an i5 2500K and was blown away by efficiency and performance even in a hobbled H67. Once I bought a proper P67, it was on. It's not that Bulldozer is terrible (because it isn't); Sandy Bridge is just a "phenom". If SB had just been a little faster than Lynnfield, it would still be fast. But it's a big leap to SB, and it's certainly the best value. AMD has Bulldozer, an inconsistent performer that is better in some areas and worse in others, but has a hard time competing with it's own forebearer. It's still an unusual product that some people will really benefit from and some wont. The demise of the Phenom II can't come soon enough for AMD as some people will look at the benchmarks and conclude that a super cheap X4 955BE is a much better value than BD. I hope it isn't seen that way, but it's not a difficult conclusion to reach. Perhaps BD is more forward looking, and the other octocore will be cheaper than the 8150 so it's a better value. I'd really like to see the performance of the 4- and 6- before making judgement.

    It's still technically a win, but it's a Pyrrhic victory.
    Reply
  • ogreslayer - Wednesday, October 12, 2011 - link

    I tell friends that exact thing all the time. Phenoms are great CPUs but switch to Nehelam or Sandy Bridge and the speed is noticibly different. At equal clocks Core 2 Quads are as fast or faster.

    Bulldozer ends up with a lot of issues fanboys refused to see even though Anandtech and other sites did bring it up in previews. I guess it was just hope and a understandable disbelief that AMD would be behind for a decade till the next architecture. We can start at clockspeed but only being dual-channel is not helping memory bandwidth. I don't think there is enough L3 and they most definitely should have a shortpipeline to crush through processes. They need an 1.4 to 1.6 in CBmarks or what is thhe point of the modules.

    The module philosophy is probably close to the future of x86 but I imagine seeing Intel keeping HT enabled on the high-end SKUs. Also I think both of them want to switch FP calculation over to GPUs.
    Reply
  • slickr - Wednesday, October 12, 2011 - link

    Yeah I agree. To me Bulldozer comes like 1 year late.

    Its just not competitive enough and the fact that you have to make a sacrifice to single threaded performance for multithreaded when even the multithreaded isn't that good and looses to 2600K is just sad.

    They needed to win big with Bulldozer and they failed hard!
    Reply
  • retrospooty - Wednesday, October 12, 2011 - link

    Ya, it seems to be a pattern lately with the last few AMD architectures.

    1. Hype up the CPU as the next big thing
    2. Release is delayed
    3. Once released, benchmarks are severely underwhelming
    Reply
  • JasperJanssen - Wednesday, October 12, 2011 - link

    4. Immediately start hyping up the next release as the salvation of all. Reply
  • GatorLord - Thursday, October 20, 2011 - link

    It looks to me like BD is the CPU beta bug sponge for Trinity and beyond. Everybody these days releases a beta before the money launch.

    Hence the B3 stepping...and probably a few more now that a capable fab is onboard with TSMC. BD is not a CPU like we're used to...its an APU/HPC engine designed to drive code and a Cayman class GPU at 28nm and lots of GHz...I get it now.

    Also, the whole massive cache and 2B transistors, 800M dedicated to I/O, thing (SB uses 995M total) finally makes sense when you realize that this chip was designed to pump many smaller GPGPU caches full of raw data to process and combine all the outputs quickly.

    Apparently GPUs compute very fast, but have slow fetch latencies and the best way to overcome that is by having their caches continously and rapidly filled...like from the CPU with the big cache and I/O machine on the same chip...how smart..and convenient...and fast.

    Can you say 'OpenCL'?
    Reply
  • jleach1 - Friday, October 21, 2011 - link

    I don't see how this can be considered an APU, This product isn't being marketed as a HPC proc., and i don't see the benefit of this architecture design in GPGPU environments at all.

    It's sad...i've always given major kudos to AMD. Back in the days of the Athlon's prime, it was awesome to see david stomping goliath.

    But AMD has dropped the ball continuously since then. Thuban was nice, but it might as well be considered a fluke, seeing as AMD took a worthy architecture (Thuban) and ditched it for what's widely considered as a joke.

    And the phrase "AMD dropped the ball" is an understatement.

    They've ultimately failed. They havent competed with Intel in years. They...have...failed. After thuban came out i was starting to think that the fact that they competed for years on price and clock speed alone was a fluke, and just a blip on the radar. Now i see it the opposite way...it seems that AMD merely puts out good processors every once in a while...and only on accident.
    Reply
  • medi01 - Wednesday, October 12, 2011 - link

    Well, if anand didn't badmouth AMD's GPU's on top of CPU's, we would see less "fanboys" complainging about anand's bias. Reply
  • vol7ron - Wednesday, October 12, 2011 - link

    By badmouth do you mean objectively tell the truth? Do you blame PCMark or FutureMark for any of that? Perhaps if all the tests just said that AMD was clearly better, it wouldn't be badmouthing anymore. Reply

Log in

Don't have an account? Sign up now