Re: [PATCH] [v4] Add idle wait support for 44x platforms

[Josh Boyer <jwboyer@linux.vnet.ibm.com>]

On Fri, 04 Apr 2008 11:28:27 -0500
Jerone Young <jyoung5@us.ibm.com> wrote:

> 2 files changed, 87 insertions(+), 1 deletion(-)
> arch/powerpc/platforms/44x/Makefile |    2 
> arch/powerpc/platforms/44x/idle.c   |   86 +++++++++++++++++++++++++++++++++++
> 
> 
> - adds MSR_DE to MSRs to enable while in wait state
> 
> This patch adds the ability for the CPU to go into wait state while in cpu_idle loop. This helps virtulization solutions know when the guest Linux kernel is in an idle state. There are two ways to do it.
> 
> 1) Command line
> 	idle=spin <-- CPU will spin (this is the default)
> 	idle=wait <-- set CPU into wait state when idle
> 
> 2) The device tree will be checked for the "/hypervisor" node
>    If this node is seen it will use "wait" for idle, so that
>    the hypervisor can know when guest Linux kernel it is in
>    an idle state.
> 
> This patch, unlike the last, isolates the code to 44x platforms.
> 
> Signed-off-by: Jerone Young <jyoung5@us.ibm.com>

This one looks great to me.  Thanks for being persistent.

I'll keep it queued up until early next week.  I've emailed the CPU
engineers to see what exactly wait state does to the core and if they
know of any issues with it.

If it comes back clean from them and we get good test results with it
enabled, then we can likely reverse the default to use it and remove
the check for the hypervisor node.

josh