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DDR3-800MHz To DDR3-2133MHz Memory Testing With AMD's Kaveri

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  • Slobodan
    replied
    If someone would made PCI expansion card containing 1GB GDDR5 memory, would Kaveri APU be able to take advantage of it (to use that memmory instead of system RAM)?

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  • mmstick
    replied
    Originally posted by Kivada View Post
    The timings are the latency, you have to calculate the timings against the Mhz you are running the ram at to see if you are actually gaining anything. Push the timings too high for a higher Mhz rating and you end up being slower then if you backed off on the MHZ and tightened up the timings.

    AMD even warns about this since many people new to overclocking do it very poorly.
    That's kind of what I already said -- and like I said, the bottleneck is not a latency bottleneck, but a bandwidth throughput bottleneck. Having lower timings will not improve the bandwidth like having higher frequencies would. The only place where timings will have an effect is with CPU-only benchmarks. With an APU, it isn't the CPU that is starved for memory, but the GPU.

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  • Dukenukemx
    replied
    Where can I get ram that says AMD Radeon? Looks pretty cool.

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  • willmore
    replied
    Memory timing

    I'd relly like to hear more on how the memory timings were set. Latency and bandwidth both can make large differences on different workloads. Many of the things already said in this thread hint at it, but I'd like to say it once and for all and in a clear way. There is one chart in the test that makes me think that the latench cycles aren't being held steady as the highest clock speed is slower than the one just one step slower.

    Latency is best measured in absolute time. You can easily calculate that from the # of clocks and the duration of one clock. The first is normally specified in the spec for the memory (and can be read from the SPD on the memory) and can be set in the BIOS. The latter is just the reciprical of the clock speed 10^9/clock speed MHz. Multiply that by the # of clock cycles and you have the absolute latency in nanoseconds.

    Testing really needs to do both variables independently. If you hold the # of clocks stead and change the clock speed, you alter both the absolute latency and the bandwidth of the memory and that confuses the results. It'll take longer--especially since messing with settings in the BIOS are never fun--but the results will be more meaningful.

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  • Kivada
    replied
    Originally posted by Drago View Post
    Expensive memory modules, I guess.
    Not really, usually within $5-10 of baseline for a given stock rating by the memory manufacturer. Nothing thats really going to blow out the budget but can make a significant difference in APU performance.

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  • Kivada
    replied
    Originally posted by mmstick View Post
    The timings don't have much affect since the bottleneck is primarily a bandwidth one rather than a latency one. I remember that it was originally planned to have GDDR5 embedded on the chip but that was canned for the first gen Kaveri -- perhaps due to budget constraints. Instead of triple channel, I don't see why they couldn't just go straight for quad channel.
    The timings are the latency, you have to calculate the timings against the Mhz you are running the ram at to see if you are actually gaining anything. Push the timings too high for a higher Mhz rating and you end up being slower then if you backed off on the MHZ and tightened up the timings.

    AMD even warns about this since many people new to overclocking do it very poorly.

    Leave a comment:


  • mmstick
    replied
    Originally posted by Rexilion View Post
    I want my new setup to be futureproof, and here are the downside's of the AMD FX 8350:
    - No PCIe 3.0 support
    - Bad single core performance
    1) PCIE 3.0 isn't needed for anything yet, even if you have have multiple high end graphics cards.
    2) Single core performance is fine in everything today -- if you want 'futureproof,' well, all future games are threaded for 8+ cores. See how the PS4 and Xbox One both feature 8 core AMD processors.

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  • Kivada
    replied
    Originally posted by jakubo View Post
    what about timings? dont they have influence on the performance?
    seeing the results i really must wonder why AMD did choose not to go all the way and go for GDDR5 and put some pressure on Intel. Or at least triple-channel...
    There where plans to do it http://www.jedec.org/standards-documents/results/gddr5m but fell through as they couldn't get the rest of the industry on board as they are just waiting for DDR4 memory as it should be around as fast.

    Basically blame Intel, if Intel had backed GDDR5m you'd see it everywhere already, but since it was only AMD pushing for it it never made it out of R&D.

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  • Slobodan
    replied
    Originally posted by Rexilion View Post
    I want my new setup to be futureproof
    Me too. I have being using my current computer (built around AMD Athlon 64 2800+) for 10+ years (from 2003.). In my opinion, HSA is the future, and that is way I have ordered A10-7850K for my new setup. At the moment its performance is not impressive but in a few years, when applications (hopefully including games) start supporting HSA, this APU will outperform even the fastest AMD and Intel "classic" CPUs.

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  • schmidtbag
    replied
    I'd be interested in a complete reverse set of tests, where the same memory module is used but at different timings. I haven't seen a memory benchmark based on timings in years, from any source.

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