linux-kernel - Intel Alder Lake Question (Scheduler)

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Message-ID: <CALGQo4Yw7Ptm5faXjyAewW9Xe5=QKC_m9=QMy4Rb0N2p-a3VuQ@mail.gmail.com>
Date:   Fri, 5 Nov 2021 07:51:04 +0000
From:   Keith Cancel <admin@...th.pro>
To:     linux-kernel@...r.kernel.org
Subject: Intel Alder Lake Question (Scheduler)

Hello,

So Alder lake was supposed to have AVX-512 disabled/fused off. So it
looks like that was not the case. For example see this news article:
https://www.anandtech.com/show/17047/the-intel-12th-gen-core-i912900k-review-hybrid-performance-brings-hybrid-complexity/2

This issue I noticed it seems to be the possibility that a bios could
allow someone to enable both AVX-512 and and E-Cores (efficiency
cores). How on earth would the scheduler handle this? I could imagine
the scheduler switching a process/thread using AVX-512 to an
efficiency core. Now suddenly the core the thread/process is running
no longer has AVX-512 instructions... This sounds like a headache.

I suppose the kernel could handle the trap and then from on only
schedule such a process on performance cores. This issue I see here
though is userland process could then intentionally trigger such a
trap to then only be scheduled on a performance core. Even if it does
not use AVX-512 otherwise.

Thanks,
Keith Cancel