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From: "gaoliming" <gaoliming@byosoft.com.cn>
To: "'Ankur Arora'" <ankur.a.arora@oracle.com>,
	<devel@edk2.groups.io>
Cc: "'Michael D Kinney'" <michael.d.kinney@intel.com>,
	"'Laszlo Ersek'" <lersek@redhat.com>
References: <20210319181421.2791425-1-ankur.a.arora@oracle.com>
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Date: Mon, 22 Mar 2021 09:40:02 +0800
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Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn>

Thanks
Liming
> -----=E9=82=AE=E4=BB=B6=E5=8E=9F=E4=BB=B6-----
> =E5=8F=91=E4=BB=B6=E4=BA=BA: Ankur Arora <ankur.a.arora@oracle.com>
> =E5=8F=91=E9=80=81=E6=97=B6=E9=97=B4: =
2021=E5=B9=B43=E6=9C=8820=E6=97=A5 2:14
> =E6=94=B6=E4=BB=B6=E4=BA=BA: devel@edk2.groups.io
> =E6=8A=84=E9=80=81: Ankur Arora <ankur.a.arora@oracle.com>; Liming Gao
> <gaoliming@byosoft.com.cn>; Michael D Kinney
> <michael.d.kinney@intel.com>; Laszlo Ersek <lersek@redhat.com>
> =E4=B8=BB=E9=A2=98: [RESEND v2] MdePkg: use CpuPause() in =
CpuDeadLoop()
>=20
> CpuPause() might allow the CPU to go into a lower power state
> state while we spin.
>=20
> On X86, CpuPause() executes a PAUSE instruction which the Intel
> and AMD specs describe as follows:
>=20
> Intel:
>   "PAUSE: An additional function of the PAUSE instruction is to reduce
>   the power consumed by a processor while executing a spin loop. A
>   processor can execute a spin-wait loop extremely quickly, causing =
the
>   processor to consume a lot of power while it waits for the resource =
it
>   is spinning on to become available. Inserting a pause instruction in =
a
>   spin-wait loop greatly reduces the processor=E2=80=99s power =
consumption."
>=20
> AMD:
>   "PAUSE: Improves the performance of spin loops, by providing a hint =
to
>   the processor that the current code is in a spin loop. The processor
>   may use this to optimize power consumption while in the spin loop.
>   Architecturally, this instruction behaves like a NOP instruction."
>=20
> On RISC-V and ARM64, CpuPause() executes a NOP, which is no worse than
> the tight loop we have.
>=20
> Cc: Liming Gao <gaoliming@byosoft.com.cn>
> Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
> Reviewed-by: Michael D Kinney <michael.d.kinney@intel.com>
> Reviewed-by: Laszlo Ersek <lersek@redhat.com>
> ---
>  MdePkg/Library/BaseLib/CpuDeadLoop.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>=20
> diff --git a/MdePkg/Library/BaseLib/CpuDeadLoop.c
> b/MdePkg/Library/BaseLib/CpuDeadLoop.c
> index 9e110cacbc96..3cd304351a65 100644
> --- a/MdePkg/Library/BaseLib/CpuDeadLoop.c
> +++ b/MdePkg/Library/BaseLib/CpuDeadLoop.c
> @@ -28,5 +28,7 @@ CpuDeadLoop (
>  {
>    volatile UINTN  Index;
>=20
> -  for (Index =3D 0; Index =3D=3D 0;);
> +  for (Index =3D 0; Index =3D=3D 0;) {
> +    CpuPause();
> +  }
>  }
> --
> 2.9.3