Messages in this thread | | | Subject | Re: [PATCH v5 28/28] x86/fpu/amx: Clear the AMX state when appropriate | From | Dave Hansen <> | Date | Mon, 24 May 2021 10:39:51 -0700 |
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On 5/24/21 10:32 AM, Len Brown wrote: > On Mon, May 24, 2021 at 10:10 AM Dave Hansen <dave.hansen@intel.com> wrote: >> On 5/23/21 8:13 PM, Andy Lutomirski wrote: >>> Can we do this just when going idle? >> Chang, you might also want to talk with folks that do scheduler >> performance work (I've cc'd Tim). I know we're always fighting to trim >> down the idle and wakeup paths. There might be no other alternative, >> but unconditionally forcing an AMX XRSTOR on return from idle might be >> considered nasty. > I'm not excited about burdening the generic idle path with a CPU > feature specific check that would need to be checked on every idle > entry.
Me neither.
But, the check itself should be cheap. A cpu_feature_enabled(AMX) check will eliminate even the cost of a branch on systems without AMX. You could probably even get fancy and also use a static branch that doesn't get enabled until the first AMX user shows up.
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