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

2021-03-25 Thread 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  代表 gaoliming
发送时间: 2021年3月22日 9:40
收件人: 'Ankur Arora' ; devel@edk2.groups.io
抄送: 'Michael D Kinney' ; 'Laszlo Ersek'

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

Reviewed-by: Liming Gao 

Thanks
Liming

-邮件原件-
发件人: Ankur Arora 
发送时间: 2021年3月20日 2:14
收件人: devel@edk2.groups.io
抄送: Ankur Arora ; Liming Gao
; Michael D Kinney
; Laszlo Ersek 
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 
Signed-off-by: Ankur Arora 
Reviewed-by: Michael D Kinney 
Reviewed-by: Laszlo Ersek 
---
  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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回复: [edk2-devel] 回复: [RESEND v2] MdePkg: use CpuPause() in CpuDeadLoop()

2021-03-24 Thread gaoliming 
Create PR https://github.com/tianocore/edk2/pull/1515

Thanks
Liming
> -邮件原件-
> 发件人: devel@edk2.groups.io  代表 gaoliming
> 发送时间: 2021年3月22日 9:40
> 收件人: 'Ankur Arora' ; devel@edk2.groups.io
> 抄送: 'Michael D Kinney' ; 'Laszlo Ersek'
> 
> 主题: [edk2-devel] 回复: [RESEND v2] MdePkg: use CpuPause() in
> CpuDeadLoop()
> 
> Reviewed-by: Liming Gao 
> 
> Thanks
> Liming
> > -邮件原件-
> > 发件人: Ankur Arora 
> > 发送时间: 2021年3月20日 2:14
> > 收件人: devel@edk2.groups.io
> > 抄送: Ankur Arora ; Liming Gao
> > ; Michael D Kinney
> > ; Laszlo Ersek 
> > 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 
> > Signed-off-by: Ankur Arora 
> > Reviewed-by: Michael D Kinney 
> > Reviewed-by: Laszlo Ersek 
> > ---
> >  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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