* Thomas Gleixner: > Having a proper interface (syscall, prctl) which user space can use to > ask for permission and allocation of the necessary buffer(s) is clearly > avoiding the downsides and provides the necessary mechanisms for proper > control and failure handling. > > It's not the end of the world if something which wants to utilize this > has do issue a syscall during detection. It does not matter whether > that's a library or just the application code itself. > > That's a one off operation and every involved entity can cache the > result in TLS. I'm not sure if it's a good idea to have each AMX consumer to set up its own TLS cache. How expensive is checking XCR0 via XGETBV instead on the AMX path? Then AMX can be enabled on the thread via a system call. It also allows disabling of AMX. It would also need an AT_HWCAP2 feature flag telling user space that AMX support is available after that system call (switching on AMX to check whether AMX paths should enabled later seems potentially wasteful if the AMX paths are never taken after all). Thanks, Florian
