Messages in this thread | | | From | Len Brown <> | Date | Fri, 23 Apr 2021 15:35:30 -0400 | Subject | Re: Candidate Linux ABI for Intel AMX and hypothetical new related features |
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n Mon, Apr 19, 2021 at 5:58 PM Borislav Petkov <bp@alien8.de> wrote: > > On Mon, Apr 19, 2021 at 05:33:03PM -0400, Len Brown wrote: > > For this to happen, every thread would not only have to include/link-with > > code that uses AMX, but that code would have to *run*. > > ...the *library* does that decision automatically! > > Which means *every* possible thread on the system. > > Which means, *every* thread has a fat 8K buffer attached to it because > the library uses AMX on its behalf by *default*.
Yes. If a library decides to execute AMX instructions on behalf of a task, the kernel will allocate an 8KB context switch buffer on behalf of that task.
True. Nothing prevents every user task in the system from executing AMX instructions, whether explicitly or in a library, and the kernel will transparently allocate an 8KB buffer for each one.
I do not know anybody who predicts or expects that every task in the system, or a universally executed library routine, will find a reason to run AMX instructions. Again, if that were the expectation or the intent, the proposal would be to statically allocate an 8KB context switch buffer on AMX hardware, instead of dynamic allocation.
Today, libraries routinely probe for what instructions are available and decide to use them, or not. I think that most customers consider that a desirable feature -- since it allows them to run the same application on multiple hardware generations and get the most out of each generation. I respect your right to dislike that feature.
Granted, if you find a reason to dislike AMX, the mechanisms to disable it today are on a system-wide basis, not on a process or task basis.
Len Brown, Intel Open Source Technology Center
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