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

["gaoliming" <gaoliming@byosoft.com.cn>]

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
> 
> 
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> 
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