19 Sep
2021
19 Sep
'21
10:05 a.m.
On Fri, Sep 17, 2021 at 03:11:49PM -0700, Larry McVoy wrote:
ARM's BIG.little architecture dates back to 2011. Of course, they
didn't *tell* anyone that they were doing this when before the chip
was released, lest it get copied by their competitors. So they
released a hacked-up version of the Linux kernel that supported their
chip. And successive versions of BIG.little implemented by different
ARM vendors had their own vendor-specific tweaks, with "board support
kernels" that were heavily hacked up Linux kernels in code that was
never sent upstream, since by the time vendors had released that chip,
their kernel team was moved to working on a new project, where they
would fork the current kernel version, and add completely different
hacks for the next year's version of their System on a Chip (SOC).
Proper support for differntly sized/powered cores didn't land in theb
ppstream Linux until 2019, when Linux 5.0 finally acquired support for
"Energy Aware Scheduling".
So not only does hardware engineering take longer, but it's done in
Sekrit, by software teams employed by chip manufacturers who often
don't have any long-time attachment to the OS, and who will get
reassigned to work the next year's SOC as soon as the current year's
SOC is released. :-(
Things have gotten a bit better in the last five years, but that's a
pretty low bar, considering how horrible things were before that!
- Ted
I'd
suggest that is not Apple, but ARM. That was sort of the whole
point of their BIG.little architecture with performance and efficiency
cores.
Credit to ARM, but M1 was where I saw it first. The M1 performance is
pretty impressive as well. Reminds me of LED bulbs: "Wait, these are
brighter, use less power, and cost less? How is that a thing?"