[PATCH RT] arm*: disable NEON in kernel mode

[Russell King - ARM Linux]

On Fri, Dec 01, 2017 at 05:58:45PM +0000, Dave Martin wrote:
> +1, at least for arm64.  I don't see a really compelling reason for
> holding kernel-mode NEON around memory management now that we have a
> strict save-once-restore-lazily model.
> 
> This may not work so well for arm though -- I haven't looked at that
> code for a while.
> 
> 
> If there is memory manamement in any core loop, you already lost
> the performance battle, and an extra
> kernel_neon_end()+kernel_neon_begin() may not be that catastrophic.

Remember that we don't permit context switches while kernel neon is
in use on ARM - if there's any possibility of scheduling to occur,
the get_cpu() in kernel_neon_begin() should trigger a schedule-while-
atomic warning.

-- 
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