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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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  • silverblue - Monday, October 17, 2011 - link

    The reason for mentioning the 2600 is because that's the only comparison we have for the moment. I don't expect Valencia to use as much power as Zambezi even on a clock-for-clock basis. Reply
  • Pipperox - Monday, October 17, 2011 - link

    That has to be seen.
    Bulldozer's HUGE 16MB of total cache surely were not put there for desktop workloads.
    Reply
  • xineis - Sunday, October 16, 2011 - link

    I am quite disappointed with the overall performance. And specially with gaming performance.

    But what about that rumored patch fix for the BDZ? Has any of you guys at AnandTech heard of that?
    Reply
  • silverblue - Sunday, October 16, 2011 - link

    You mean this one?

    http://quinetiam.com/?p=2356

    Interesting if it's true, however it's doubtful to help across the board (pun not intended). Still, very good news for those doing rendering/encoding.
    Reply
  • richaron - Sunday, October 16, 2011 - link

    I never want to see a link to that dickbag again..
    His blogs about WW3, bigfoot, & 2012 should be enough to give you an idea. Also, the dudes at Kubuntu basically do repackaging & KDE integration. They don't touch hardware.
    No doubt there can be significant gains through software. But I would rather stab myself through the eyelid than read anything more by that 'person'.
    Reply
  • xineis - Sunday, October 16, 2011 - link

    Yeah, that one. I know that there is a very slim chance of that 40% boost ever happening, but the idea behind the "patch" is actually plausible.

    I've seen lots of people explaning how would it work and it looks somewaht legit.

    Granted that 40% is too much, but if the right tweaking, I'd be more than happy with 20% to 30% increase in performance!
    Reply
  • richaron - Monday, October 17, 2011 - link

    everyone would be happy with 20-30%. It doesn't seem realistic to me... but i dropped out of computer engineering :p

    From what I've seen, I would guess about 5% [+/- 5%]
    Reply
  • silverblue - Monday, October 17, 2011 - link

    Turns out he was one giant troll, or seemingly so. Now, he's pointing the finger at...

    "Problem solved, it’s just a thermal protection issue, people have been pushing voltages too high. Maybe there’s some variance in mainboard chipsets, but some overclockers and hitting really good numbers."

    Really? After all that hoo-har about registry patches, BIOS flashes and the like, we're now blaming thermal protection? I'm taking this with a litre of Dead Sea water.
    Reply
  • silverblue - Monday, October 17, 2011 - link

    Hey, there has to be somebody somewhere that we can all laugh at. ;)

    That said, he does sound a bit... odd.
    Reply
  • Romulous - Monday, October 17, 2011 - link

    perhaps Bulldozer.Next will actually work ;) Reply

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