IPC Increases: Double L1 Data Cache, Better Branch Prediction

One of the biggest changes in the design is the increase in the L1 data cache, doubling its size from 64 KB to 128 KB while keeping the same efficiency. This is combined with a better prefetch pipeline and branch prediction to reduce the level of cache misses in the design. The L1 data cache is also now an 8-way associative design, but with the better branch prediction when needed it will only activate the one segment required and when possible power down the rest.  This includes removing extra data from 64-bit word constructions. This reduces power consumption by up to 2x, along with better clock gating and minor adjustments. It is worth pointing out that doubling the L1 cache is not always easy – it needs to be close to the branch predictors and prefetch buffers in order to be effective, but it also requires space. By using the high density libraries this was achieved, as well as prioritizing lower level cache. Another element is the latency, which normally has to be increased when a cache increases in size, although AMD did not elaborate into how this was performed.

As listed above, the branch prediction benefits come about through a 50% increase in the BTB size. This allows the buffer to store more historic records of previous interactions, increasing the likelihood of a prefetch if similar work is in motion. If this requires floating point data, the FP port can initiate a quicker flush required to loop data back into the next command. Support for new instructions is not new, though AVX2 is something a number of high end software packages will be interested in using in the future.

These changes, according to AMD, relate to a 4-15% higher IPC for Excavator in Carrizo compared to Steamroller in Kaveri.  This is perhaps a little more what we normally would expect from a generational increase (4-8% is more normal), but AMD likes to stress that this comes in addition to lower power consumption and with a reduced die area. As a result, at the same power Carrizo can have both an IPC advantage and a frequency advantage.

As a result, AMD states that for the same power, Cinebench single threaded results will go up 40% and multithreaded results up 55%. The benefits are fewer however the further up the power band you go despite the increase, as the higher density libraries perform slightly worse at higher power than Kaveri.

Efficiency and Die Area Savings Power Saving and Power Consumption
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  • Refuge - Wednesday, June 3, 2015 - link

    Built my mother a new system from her old scraps with a new A8, she loves that desktop, and when she put an SSD in it finally she loved it ten times more. the upgrade only cost her $300, for CPU, Mobo, RAM. Threw it together in 45 minutes, and she hasn't had a problem with it in 2 years so far. Reply
  • nathanddrews - Wednesday, June 3, 2015 - link

    I prefer the following setup:
    1. Beast-mode, high-performance desktop for gaming, video editing, etc.
    2. Low-power, cheap notebook/tablet for In-Home Steam Streaming and light gaming (720p) on the go.

    In my use case, as long as I can load and play the game (20-30fps for RTS, 30fps+ for everything else) on a plane ride or some other scenario without AC access, I'm not really concerned with the AA or texture quality. I still want to get the best experience possible, but balanced against the cheapest possible price. The sub-$300 range is ideal for me.
    Reply
  • AS118 - Wednesday, June 3, 2015 - link

    Yeah, that's my thing as well. High resolutions at work, and at home, 768p or 900p's just fine, especially for gaming.

    I also recommend AMD to friends and relatives who want laptops and stuff that can do casual gaming for cheap.
    Reply
  • FlushedBubblyJock - Tuesday, June 9, 2015 - link

    Why go amd when HD3000 does just fine gaming and the added power of the intel cpu is an awesome boost overall ... Reply
  • Valantar - Wednesday, June 3, 2015 - link

    1366*768 on anything larger than 13" looks a mess, but in a cheap laptop I'd rather have a 13*7 IPS for the viewing angles and better visuals than a cheap FHD TN panel - bad viewing angles especially KILL the experience of using a laptop. Still, 13*7 is pretty lousy for anything other than multimedia - it's simply too short to fit a useful amount of text vertically. A decent compromise would be moving up to 1600*900 as the standard resolution on >11" displays. Or, of course, moving to 3:2 or 4:3 displays, which would make the resolution 1366*911 or 1366*1024 and provide ample vertical space. Still, 13*7 TN panels need to go away. Now. Reply
  • yankeeDDL - Wednesday, June 3, 2015 - link

    Like I said, to each his own. I have a Lenovo Z50 which I paid less than $470 with the A10 7300.
    Quite frankly, I could not be happier and I think it provides a massive value for that money.
    Sure, a larger battery and a better screen would not hurt, but for hustling it around the house, or bring it to friend/family house, watch movies, play games at native resolution, it is fantastic.
    It's no road warrior, for sure (heavy and the battery life doesn't go much beyond 3hrs of "serious" use) but playing at 1366*768 on something that weights 5 pounds and costs noticeably less than $500, is quite amazing. Impossible on an Intel+discrete graphics, as far as I know.
    Reply
  • FlushedBubblyJock - Tuesday, June 9, 2015 - link

    Nope, HD3000 plays just fine Reply
  • Margalus - Wednesday, June 3, 2015 - link

    I'd rather have a cheaper 15.6" 1366x768 TN panel over a more expensive smaller ips panel. Reply
  • UtilityMax - Wednesday, June 3, 2015 - link

    1366x768 is fine for movies and games. But it's a bad resolution for reading text or viewing images on the web, since you see pixels the size of moon crater. Reply
  • BrokenCrayons - Thursday, June 4, 2015 - link

    I understand there's going to be a variety of differing opinions on the idea of seeing individual pixels. As far as I'm concerned, seeing individual pixels isn't a dreadful or horrific thing. In fact, to me it simply doesn't matter. I'm busy living my meat world life and enjoying whatever moments I have with family and friends so I don't give the ability to discern an individual pixel so much as a second thought. It is an insignificant part of my life, but what isn't is the associated decline in battery life (on relative terms) required to drive additional, utterly unnecessary pixels and to push out sufficient light as a result of the larger multitude of them. That sort of thing is marginally annoying -- then again, I still just don't care that much one way or another aside from noticing that a lot of people are very much infatuated with an insignificant, nonsense problem. Reply

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