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How would x86-64 be as efficient with the same transistor & power budget when they have to run an extra decoder and ring within that budget? Seems physically im
by jorvi 4y ago
How would x86-64 be as efficient with the same transistor & power budget when they have to run an extra decoder and ring within that budget? Seems physically impossible.
- Salgat 4y agoMy guess is it's related to the higher transistor count. The M1 for example has 16B transistors compared to the 5800U with 10.7B.
- Panzer04 4y agoAs I understand it, the actual processing part of most chips nowadays is fairly bespoke, with a decoder sitting on top. I doubt decode can make up that large a portion of a chips power consumption (probably negligible next to the rest of the chip?), so other improvements can make up for the difference.
- ejiblabahaba 4y agoI found this to be a pretty expansive answer to this question: https://chipsandcheese.com/2021/07/13/arm-or-x86-isa-doesnt-matter/ https://chipsandcheese.com/2021/07/13/arm-or-x86-isa-doesnt-...
- jorvi 4y agoThank you for the detailed article!
- jabl 4y agoAll else being equal, they can't. But the difference isn't as big as some people like to think. For a current high end core, probably low single digit %. And x86-64 has had a lot more effort going into software optimization.
- monocasa 4y agoBecause the more complex decoder is traded in this case for a denser instruction set, which means they can trade it for less instruction cache (which is more power hungry).
- chasil 4y agoHow can AArch64 be as efficient when it implements all of the old 32-bit extensions? Some don't, but a phone does.
- appointment 4y agoThe latest ARM Cortex CPUs (models X2, A715 and A510) drop 32-bit support. Qualcomm actually includes two older Cortex-A710 cores in the Snapdragon 8 gen 2 for 32-bit support. Don't know much about Apple Silicon but didn't they drop 32-bit a couple of years back? Google has purged 32-bit apps from the official Android app store, but as I understand it the Chinese OEMs that ship un-Googled AOSP ROMs with their own app stores haven't been as aggressive about moving to 64-bit.
- deleted 4y ago[deleted]
- shaunsingh0207 4y agoApple also entirely drops 32-bit from their arm systems
- snovv_crash 4y agoThe decoder has negligible power consumption and die area on a modern CPU.
- zozbot234 4y agoNot if you have a complex ISA like x86 and want a very wide decode.
- peoplefromibiza 4y agoyes if you want to keep the transistor count low M1 has 16 billion of them AMD is below 10 billion
- peoplefromibiza 4y ago> when they have to run an extra decoder it's not that expensive it's a tradeoff, you lose something there, you gain somewhere else. x86 has a more complex decoder exactly because it was less powerful and had to save on computing power and energy consumption, not being a mainframe.