Re: [PATCH v3 2/3] x86/fpu: Add a helper to prepare AMX state for low-power CPU idle

From: Chang S. Bae
Date: Mon Apr 04 2022 - 20:45:53 EST

On 4/3/2022 9:37 AM, Thomas Gleixner wrote:
On Thu, Mar 24 2022 at 19:22, Chang S. Bae wrote:
When a CPU enters an idle state, non-initialized states left in large
registers may be the cause of preventing deeper low-power states.

The new helper ensures the AMX state is initialized to make the CPU
ready for low-power states. It will be used by the intel idle driver.

What about AVX...AVX512? Are they harmless in that regard?

I double-checked with HW folks. Yes, that's the case. Their state whether initialized or not does not prevent the processor from entering a deeper low-power state.

If so, then the first sentence above is confusing and should clearly
spell out that it's AMX which causes that problem.

I see. Will do that.