[Xen-devel] [Patch v2] xen/x86: Be more power-efficient when waiting forever

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

The effect is unchanged, but the processor will be spending most of its time
in the C1 or C1E power state rather than C0.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Acked-by: Keir Fraser <keir@xxxxxxx>
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: George Dunlap <george.dunlap@xxxxxxxxxxxxx>

---

Changes in v2:
 * Only change do_early_page_fault().  Leave the EFI dead code till 4.5

This was discovered while I was playing about in the early_page_fault()
handler with the IBM box which was corruption the Xen code section.

There is one final for(;;); loop, but is in common code and immediately
following a call to panic(), so is actually dead code and will be cleaned up
in v2 of my "noreturn" series at the start of 4.5

George: I am requesting that this get a freeze exception, under the
qualification of #2 "An awesome release", given no function change threatening
---
 xen/arch/x86/traps.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c
index d8b3eac..8c355e5 100644
--- a/xen/arch/x86/traps.c
+++ b/xen/arch/x86/traps.c
@@ -1448,7 +1448,8 @@ void __init do_early_page_fault(struct cpu_user_regs 
*regs)
         printk("Stack dump: ");
         while ( ((long)stk & ((PAGE_SIZE - 1) & ~(BYTES_PER_LONG - 1))) != 0 )
             printk("%p ", _p(*stk++));
-        for ( ; ; ) ;
+        for ( ; ; )
+            halt();
     }
 }
 
-- 
1.7.10.4


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