Messages in this thread | | | From | Florian Weimer <> | Subject | Re: Candidate Linux ABI for Intel AMX and hypothetical new related features | Date | Fri, 21 May 2021 18:19:09 +0200 |
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* Dave Hansen:
> On 5/21/21 7:44 AM, Florian Weimer wrote: >> * Dave Hansen via Libc-alpha: >>> Our system calls are *REALLY* fast. We can even do a vsyscall for this >>> if we want to get the overhead down near zero. Userspace can also cache >>> the "I did the prctl()" state in thread-local storage if it wants to >>> avoid the syscall. >> Why can't userspace look at XCR0 to make the decision? > > The thing we're trying to avoid is a #NM exception from XFD (the new > first-use detection feature) that occurs on the first use of AMX. > XCR0 will have XCR0[AMX]=1, even if XFD is "armed" and ready to > generate the #NM.
I see. So essentially the hardware wants to offer transparent initialize-on-use, but Linux does not seem to want to implement it this way.
Is there still a chance to bring the hardware and Linux into alignment?
Thanks, Florian
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