Re: [PATCH] xen/x86: Be more power-efficient when waiting forever

[Keir Fraser <keir.xen@gmail.com>]

On 02/12/2013 14:38, "Andrew Cooper" <andrew.cooper3@citrix.com> wrote:

> 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@citrix.com>
> CC: Keir Fraser <keir@xen.org>
> CC: Jan Beulich <JBeulich@suse.com>
> CC: George Dunlap <george.dunlap@eu.citrix.com>

Acked-by: Keir Fraser <keir@xen.org>

> ---
> 
> 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/efi/boot.c |    3 ++-
>  xen/arch/x86/traps.c    |    3 ++-
>  2 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/xen/arch/x86/efi/boot.c b/xen/arch/x86/efi/boot.c
> index 0dd935c..602cc12 100644
> --- a/xen/arch/x86/efi/boot.c
> +++ b/xen/arch/x86/efi/boot.c
> @@ -201,7 +201,8 @@ static void __init __attribute__((__noreturn__))
> blexit(const CHAR16 *str)
>          efi_bs->FreePages(xsm.addr, PFN_UP(xsm.size));
>  
>      efi_bs->Exit(efi_ih, EFI_SUCCESS, 0, NULL);
> -    for( ; ; ); /* not reached */
> +    for ( ; ; ) /* not reached */
> +        halt();
>  }
>  
>  /* generic routine for printing error messages */
> 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();
>      }
>  }
>