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

["Ankur Arora" <ankur.a.arora@oracle.com>]

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.arora@oracle.com>; devel@edk2.groups.io
>> 抄送: 'Michael D Kinney' <michael.d.kinney@intel.com>; 'Laszlo Ersek'
>> <lersek@redhat.com>
>> 主题: [edk2-devel] 回复: [RESEND v2] MdePkg: use CpuPause() in
>> CpuDeadLoop()
>>
>> Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn>
>>
>> Thanks
>> Liming
>>> -----邮件原件-----
>>> 发件人: Ankur Arora <ankur.a.arora@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.arora@oracle.com>; Liming Gao
>>> <gaoliming@byosoft.com.cn>; Michael D Kinney
>>> <michael.d.kinney@intel.com>; Laszlo Ersek <lersek@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 <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(-)
>>>
>>> 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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