Messages in this thread | | | Date | Mon, 24 May 2021 21:47:53 -0700 | From | "Andy Lutomirski" <> | Subject | Re: [PATCH v5 24/28] x86/fpu/xstate: Use per-task xstate mask for saving xstate in signal frame |
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On Mon, May 24, 2021, at 11:06 AM, Len Brown wrote: > On Sun, May 23, 2021 at 11:15 PM Andy Lutomirski <luto@kernel.org> wrote: > > > > If I'm reading this right, it means that tasks that have ever used AMX > > get one format and tasks that haven't get another one. > > No. The format of the XSTATE on the signal stack is uncompressed XSAVE > format for both AMX and non-AMX tasks, both before and after this patch. > That is because XSAVE gets the format from XCR0. It gets the fields > to write from the run-time parameter. > > So the change here allows a non-AMX task to skip writing data (zeros) > to the AMX region of its XSTATE buffer.
I misread the patch. I still think this patch is useless.
> > The subsequent patch adds the further optimization of (manually) checking > for INIT state for an AMX-task and also skip writing data (zeros) in that case. > > We should have done this optimization for AVX-512, but instead we > guaranteed writing zeros, which I think is a waste of both transfer time > and cache footprint.
If no one depends on it, it’s not ABI.
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