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A comment on A Suprising Discovery Inside the Steam Deck's APU. Parent comment

Re:A Suprising Discovery Inside the Steam Deck's APU by jsheard on Sunday January 14, 2024 @07:54PM (#38996109)
They did, but to get it running as well as they did they had to deviate from generic ARM by adding support for the x86 memory model in hardware. Apple was in a position to do that since they design their own ARM cores anyway, but the off-the-shelf ARM reference designs that most other players are relying on don't have that capability.
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Re:A Suprising Discovery Inside the Steam Deck's APU by saagarjha on Sunday January 14, 2024 @08:25PM (#38996330)
You can do it with standard ARM instructions these days.
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[dead]
Re:A Suprising Discovery Inside the Steam Deck's APU by erik on Monday January 15, 2024 @03:16AM (#38998500)
I vouched for this comment, but it looks like you're shadow banned. You might want to email support.
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Re:A Suprising Discovery Inside the Steam Deck's APU by mhh__ on Monday January 15, 2024 @02:32AM (#38998284)
> these days

Which instructions?

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Re:A Suprising Discovery Inside the Steam Deck's APU by saagarjha on Monday January 15, 2024 @03:19AM (#38998518)
Those that are part of FEAT_LRCPC.
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Re:A Suprising Discovery Inside the Steam Deck's APU by lonjil on Monday January 15, 2024 @04:53AM (#38999009)
> They did, but to get it running as well as they did they had to deviate from generic ARM by adding support for the x86 memory model in hardware.

Note that this is actually very cheap in hardware. All ARM CPUs already support memory accesses that behave similarly to x86. It's just that they're special instructions meant for atomics. Most load and store instructions in Aarch64 don't have such variants, because it'd use a lot of instruction encoding space. The TSO bit in Apple's CPUs is really more of an encoding trick, to allow having a large number of "atomic" memory instructions without needing to actually add lots of new instructions.

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