Re: 回复: [edk2-devel] 回复: [RESEND v2] MdePkg: use CpuPause() in CpuDeadLoop()

[Ankur Arora]

On 2021-03-24 8:15 p.m., gaoliming wrote:

Create PR https://github.com/tianocore/edk2/pull/1515

Thanks Liming.

Ankur

Thanks
Liming

-----邮件原件-----
发件人: devel@edk2.groups.io <devel@edk2.groups.io> 代表 gaoliming
发送时间: 2021年3月22日 9:40
收件人: 'Ankur Arora' <ankur.a.ar...@oracle.com>; devel@edk2.groups.io
抄送: 'Michael D Kinney' <michael.d.kin...@intel.com>; 'Laszlo Ersek'
<ler...@redhat.com>
主题: [edk2-devel] 回复: [RESEND v2] MdePkg: use CpuPause() in
CpuDeadLoop()

Reviewed-by: Liming Gao <gaolim...@byosoft.com.cn>

Thanks
Liming

-----邮件原件-----
发件人: Ankur Arora <ankur.a.ar...@oracle.com>
发送时间: 2021年3月20日 2:14
收件人: devel@edk2.groups.io
抄送: Ankur Arora <ankur.a.ar...@oracle.com>; Liming Gao
<gaolim...@byosoft.com.cn>; Michael D Kinney
<michael.d.kin...@intel.com>; Laszlo Ersek <ler...@redhat.com>
主题: [RESEND v2] MdePkg: use CpuPause() in CpuDeadLoop()

CpuPause() might allow the CPU to go into a lower power state
state while we spin.

On X86, CpuPause() executes a PAUSE instruction which the Intel
and AMD specs describe as follows:

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’s power consumption."

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."

On RISC-V and ARM64, CpuPause() executes a NOP, which is no worse than
the tight loop we have.

Cc: Liming Gao <gaolim...@byosoft.com.cn>
Signed-off-by: Ankur Arora <ankur.a.ar...@oracle.com>
Reviewed-by: Michael D Kinney <michael.d.kin...@intel.com>
Reviewed-by: Laszlo Ersek <ler...@redhat.com>
---
  MdePkg/Library/BaseLib/CpuDeadLoop.c | 4 +++-
  1 file changed, 3 insertions(+), 1 deletion(-)

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;

-  for (Index = 0; Index == 0;);
+  for (Index = 0; Index == 0;) {
+    CpuPause();
+  }
  }
--
2.9.3

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