So although the Cortex-A715 is at least noticeably more power efficient than the Cortex-A710, the Cortex-A715 is still slightly less power efficient compared to the Cortex-A78 (although the Cortex-A715 has a noticeably higher single core score than the Cortex-A78 at ~1.7 W).
Interesting, so A715 dropping 32-bit support and having some stuff redesigned to claw back efficiency wasn't able to get all the way back to A78 levels. Also the V/F curve seemed to get shifted to the right a bit? So for the power range of something like the Switch, the A78's still ideal. It's probably when you go up to something like laptop range where the A715 becomes preferable.
@oldpuck Let's say the delay allowed significant changes to the memory controller, e.g. a switch from mobile ram to desktop ram, could said changes improve Drake's single threaded performance and allow a similar hardware profile?
So as ILikeFeet mentioned, it's a loss in perf/watt. Because regular DDR needs more energy to push each bit, so it'll always lose in that regard. (energy per bit-wise, LPDDR should beat GDDR, then GDDR should beat regular DDR)
Aside from that, those DDR DIMMs/sticks are probably physically too big for the Switch form factor? (ah, but why not SO-DIMMs, you might ask. Apparently they hit a wall at 6400 MT/s)
If there were any advantages in performance, regular DDR
probably should be a bit better in latency (I think that as latency goes,
historically, regular DDR beats LPDDR, then LPDDR beats GDDR)? But probably not by enough to offset the energy efficiency loss. You're also not necessarily winning in raw bandwidth either.
As theoretical bandwidth goes, DDR5 is currently standardized up to 7600 MT/s. LPDDR5 goes up to 6400 MT/s and 5X up to 8533 MT/s. Yes, you as an individual consumer can buy DDR5 sticks that go beyond 7600 MT/s. They're not standardized. Device manufacturers therefore will not make promises as to support those higher speeds. You go beyond JEDEC speeds, you are technically on your own.
Also, memory controllers aren't up to snuff quite yet, I think? Intel, as of Raptor Lake, doesn't guarantee Gear 2* beyond 5600 MT/s. I'm less knowledgeable about AMD's side of things, though I am aware that that the 'sweet spot' for Zen 4 is 6000 MT/s, which suggests a limitation either with the memory controller, the Infinity Fabric, or both.
Random aside: I actually am curious why memory controllers for LPDDR seem to handle higher speeds than DDR. Does that historical trend of having somewhat worse latency mean that there's less stress, relatively speaking? Does it help that LPDDR modules tend to be soldered and have less distance to cover leading to having an easier time with maintaining signal integrity? (that's the issue with SO-DIMMs, thus leading to the new CAMM standard)
*so in a few posts related to RAM, I've mentioned things like "Gear 1" and "Gear 2". Maybe I should explain what I'm referring to.
With RAM, you see speed in MT/s; MegaTransfers per Second. Why 'Transfers'? Remember that DDR standards for 'Double Data Rate'; you Transfer data twice per clock cycle. Ergo, the actual frequency that the ram stick runs at is half of the MT/s. So 6400 MT/s is 3200 Mhz.
Historically, the memory controller by default attempted to run at the same frequency as the ram. Recently (as of Rocket Lake in 2021, I believe), Intel introduced new terminology and referred to that as 'Gear 1'; IMC (Integrated Memory Controller) running at ram speed divided by 1. 'Gear 2' would then be the IMC running at ram speed divided by 2. The plus side is that this allows for the usage of faster RAM sticks for more bandwidth. The downside is the IMC running slower tanks your latency. It actually ends up such that, on average (and for typical consumers, at least), with currently existing software, with DDR4, you're better off with the higher end of what you can maintain in Gear 1, than going further with Gear 2, as latency is just that important in the present. With DDR5, Intel doesn't do Gear 1. I think that the options are Gear 2 and 4 (so yes, ram speed divided by 4). I'm less clear with AMD, but typically the concern there is pushing not too hard to accidentally end up desynching with the Infinity Fabric and causing
that to lower itself down to half speed.
Unfortunately, I have no idea how the latency of DDR5 in Gear 4 would compare against LPDDR.