Re: [PATCH v5] drm/i915: Use SSE4.1 movntdqa to accelerate reads from WC memory

Chris Wilson
2016-07-18T10:01:33Z

On Mon, Jul 18, 2016 at 10:31:05AM +0100, Tvrtko Ursulin wrote:
> On 16/07/16 16:44, Chris Wilson wrote:
> Is it okay nowadays to just use these registers in the kernel?
>
> Many years ago when I last looked into this FPU and MMX registers
> were discouraged against and needed explicit kernel_gpu_begin/end
> around the block. Since they were not saved/restored by the kernel
> and doing otherwise would mess up the userspace context.
>
> Perhaps these new registers are different or the things have
> generally changed since then?

Hmm, I thought kernel_fpu_begin() was explicitly to handle the lack of
context save/restore of the FPU registers (a different block to the xmm
registers). However, I missed that the existing sse2/avx2 also uses it.
-Chris

--
Chris Wilson, Intel Open Source Technology Centre