[RESEND v2] MdePkg: use CpuPause() in CpuDeadLoop()

[RESEND v2] MdePkg: use CpuPause() in CpuDeadLoop()

[Ankur Arora]

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

回复: [RESEND v2] MdePkg: use CpuPause() in CpuDeadLoop()

[gaoliming]

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

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

[gaoliming]

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

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
> 
> 
> 
> 
> 
> 
> 

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.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
>>
>>
>>
>>
>>
>> 
>>
> 
> 
>