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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