Cache and Memory Performance

I mentioned earlier that cache latencies are higher in order to accommodate the larger caches (8MB L2 + 8MB L3) as well as the high frequency design. We turned to our old friend cachemem to measure these latencies in clocks:

Cache/Memory Latency Comparison
  L1 L2 L3 Main Memory
AMD FX-8150 (3.6GHz) 4 21 65 195
AMD Phenom II X4 975 BE (3.6GHz) 3 15 59 182
AMD Phenom II X6 1100T (3.3GHz) 3 14 55 157
Intel Core i5 2500K (3.3GHz) 4 11 25 148

Cache latencies are up significantly across the board, which is to be expected given the increase in pipeline depth as well as cache size. But is Bulldozer able to overcome the increase through higher clocks? To find out we have to convert latency in clocks to latency in nanoseconds:

Memory Latency

We disable turbo in order to get predictable clock speeds, which lets us accurately calculate memory latency in ns. The FX-8150 at 3.6GHz has a longer trip down memory lane than its predecessor, also at 3.6GHz. The higher latency caches play a role in this as they are necessary to help drive AMD's frequency up. What happens if we turn turbo on and peg the FX-8150 at 3.9GHz? Memory latency goes down. Bulldozer still isn't able to get to main memory as quickly as Sandy Bridge, but thanks to Turbo Core it's able to do so better than the outgoing Phenom II.

L3 Cache Latency

L3 access latency is effectively a wash compared to the Phenom II thanks to the higher clock speeds enabled by Turbo Core. Latencies haven't really improved though, and Bulldozer has a long way to go before it reaches Sandy Bridge access latencies.

The Impact of Bulldozer's Pipeline Windows 7 Application Performance
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  • Saxie81 - Wednesday, October 12, 2011 - link

    Ouch.... Not looking good. :S

    Thanks for the reply, again great review!!
    Reply
  • velis - Wednesday, October 12, 2011 - link

    Ignoring the power consumption it seems to me that @4.6GHz it should start being quite competitive.
    So can we expect base clocks to rise once significant volume of these chips starts getting out and GloFo refines the process?
    I also must admit I didn't expect 2 bn transistors. All the time AMD was bragging about how much they saved and then we get this behemoth. No wonder they have process issues. Such big chips always do.
    Reply
  • cfaalm - Wednesday, October 12, 2011 - link

    Well it is an 8-core, not a 4 core. 2x 995M (Sandybridge 4C) almost 2B, though I am sure the multply isn't exactly correct. A lot of it depens on the L3/L2 RAM amounts. The savings seem to be minimal.

    I am still confused about why they so deliberately chose to go with a relatively low single thread performance. My main application is multithreaded, but since it's such a mixed bag overall I am pretty unsure if this will be my next CPU, unless I get to see convincing Cubase 6 benchies. For an FX moniker it needs to perform better than this anyway.

    I'll throw in a lyric from The Fixx
    "It doesn't mean much now, it's built for the future."
    Reply
  • TekDemon - Wednesday, October 12, 2011 - link

    Wow, no wonder they say you need water cooling or better to go 5Ghz+. Reply
  • enterco - Wednesday, October 12, 2011 - link

    AMD should send a developer team to CryTek to help them release a patch able to use more cores :) Reply
  • medi01 - Wednesday, October 12, 2011 - link

    Uhm, what about other numbers? Reply
  • IlllI - Wednesday, October 12, 2011 - link

    this might be the final nail in the coffin. We might have to wait longer for it to be competitive? People have literally been waiting for -years- for amd to catch up.
    probably by the time piledriver(or whatever it'll be called) comes out, ib will be out (and even further behind intel)

    btw I think tomshardware tested it with windows 8 and it was still a turd.

    I seriously hope you can get some answers/reasons why amd released such a woeful product. Maybe this was why dirk was fired? All I know is after 7+ years of amd, my next processor will be intel
    Reply
  • Ushio01 - Wednesday, October 12, 2011 - link

    Desktop CPU's are Halo parts and as such are irrelevant. It's the Server and OEM Laptop CPU's were AMD needs to perform and AMD's server share just keeps dropping. Reply
  • lyeoh - Wednesday, October 12, 2011 - link

    Thing is I wouldn't want to use them in my servers: http://us.generation-nt.com/answer/patch-x86-amd-c...

    FWIW when the Athlon64s first came out, we bought a bunch of them, they were not bad, but there were clock issues - the TSCs weren't synchronized. So had to set idle=poll (and thus using more watts).

    You can blame the OS developers, but most people buy new hardware to run existing operating systems and programs on, not future unreleased ones.

    It sure is looking bad for them. I won't be buying AMD CPUs but I hope the fanboys keep them alive ;).
    Reply
  • OCedHrt - Wednesday, October 12, 2011 - link

    "Other than the 8150, only the quad-core FX processors are able to exceed the 3.3GHz clock speed of the Phenom II X6 1100T."

    The 6 core FX is also clocked higher?
    Reply

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