News for hackers. Stuff that matters.

A comment on I love ARM. Parent comment

Re:I love ARM by saagarjha on Wednesday July 29, 2020 @11:41AM (#23987906)
Apple couldn’t care less; they are supposed to support 4K pages in hardware but they do not on recent chips.
[ Parent | on HN ]
Re:I love ARM by rrss on Wednesday July 29, 2020 @12:06PM (#23988320)
ARMv8-A supports page sizes of 4k, 16k, and 64k. The specification permits implementations to choose which of these page sizes to implement. See the register ID_AA64MMFR0_EL1.
[ Parent | on HN ]
Re:I love ARM by saagarjha on Wednesday July 29, 2020 @12:37PM (#23988673)
I'm not an expert, but I believe 4K support is required? Apple doesn't do that; they just have 16K granules (which I forsee as being problematic with compatibility as they bring these over to macOS).
[ Parent | on HN ]
Re:I love ARM by rrss on Wednesday July 29, 2020 @04:29PM (#23991226)
> I believe 4K support is required?

As I said, I don't think that's the case. ARMv8-A supports the 3 page sizes and has a register so that implementations can advertise which are supported.

> Armv8-A supports three different granule sizes: 4KB, 16KB, and 64KB.

> The granule sizes that a processor supports are IMPLEMENTATION DEFINED and are reported by ID_AA64MMFR0_EL1

https://developer.arm.com/architectures/learn-the-architectu...

[ Parent | on HN ]
Re:I love ARM by saagarjha on Sunday August 02, 2020 @08:05PM (#24032862)
You know I asked around recently and it seems to be that all three are now optional. Perhaps Apple has pushed for this, because I recall 4K and 64K support being a hard requirement.
[ Parent | on HN ]