Re: [kvm-ppc-devel] [PATCH 1 of 2] Add idle power save for ppc

[Jerone Young <jyoung5@us.ibm.com>]

On Wed, 2008-04-02 at 08:14 -0400, Jimi Xenidis wrote:
> On Apr 2, 2008, at 3:52 AM, Jerone Young wrote:
> 
> > # HG changeset patch
> > # User Jerone Young <jyoung5@us.ibm.com>
> > # Date 1207122427 18000
> > # Node ID 6e9ae9e1e5992339ca1f3efa93f8200cf24cbee5
> > # Parent  1506aa38ddabb0bf73fff3ac3f3db5f9ef6458cc
> > Add idle power save for ppc 4xx for 2.6.25
> >
> > This patch sets the wait state MSR when power_save is called in  
> > cpu_idle loop for ppc4xx. This is mainly to help out virtualization  
> > solutions such as KVM. This way the virtualization soultions are  
> > able to tell if the guest kernel is idle.
> >
> > I have tested this on hardware & KVM virtual guest.
> >
> > The issue though is this is a temporary patch. As the one that will  
> > be sent upstream is based on linux-next (2.6.26) and is not the  
> > same as the 2.6.25 patch.
> >
> > Signed-off-by: Jerone Young <jyoung5@us.ibm.com>
> >
> > diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/ 
> > Makefile
> > --- a/arch/powerpc/kernel/Makefile
> > +++ b/arch/powerpc/kernel/Makefile
> > @@ -39,6 +39,7 @@ obj-$(CONFIG_GENERIC_TBSYNC)	+= smp-tbsy
> >  obj-$(CONFIG_GENERIC_TBSYNC)	+= smp-tbsync.o
> >  obj-$(CONFIG_CRASH_DUMP)	+= crash_dump.o
> >  obj-$(CONFIG_6xx)		+= idle_6xx.o l2cr_6xx.o cpu_setup_6xx.o
> > +obj-$(CONFIG_4xx)		+= idle_4xx.o
> >  obj-$(CONFIG_TAU)		+= tau_6xx.o
> >  obj-$(CONFIG_HIBERNATION)	+= swsusp.o suspend.o \
> >  				   swsusp_$(CONFIG_WORD_SIZE).o
> > diff --git a/arch/powerpc/kernel/idle_4xx.c b/arch/powerpc/kernel/ 
> > idle_4xx.c
> > new file mode 100644
> > --- /dev/null
> > +++ b/arch/powerpc/kernel/idle_4xx.c
> > @@ -0,0 +1,22 @@
> > +/*
> > + * This file contains the power_save function for 4xx CPUs
> > + *
> > + * added by Jerone Young <jyoung5@us.ibm.com>
> > + *
> > + * This program is free software; you can redistribute it and/or
> > + * modify it under the terms of the GNU General Public License
> > + * as published by the Free Software Foundation; either version
> > + * 2 of the License, or (at your option) any later version.
> > + */
> > +
> > +#include <asm/processor.h>
> > +#include <asm/machdep.h>
> > +
> > +void ppc4xx_idle(void)
> > +{
> > +	unsigned long msr_save;
> > +
> > +	/* set wait state MSR */
> > +	msr_save = mfmsr();
> > +	mtmsr(msr_save|MSR_WE|MSR_EE|MSR_CE);
> 
> 1) I think you also want MSR_DE here, no?
> 2) Just to be safe, I'd also append an isync();
> 3) In case MSR_WE does nothing, or continues from here I'd append  
> "mstmsr(msr_save); isync();" as well

Looks like using local_irq_enable() just might have been a better idea
after all. 

So the MSR_DE is yet another case that could go here. If it was on
coming into power_save...I'm assuming it would get disabled by
local_irq_disable().

Looks like using isync after the mtmsr looks to be a good safety net.

> 
> -JX
> 
> 
> 
> > +}
> > diff --git a/arch/powerpc/kernel/setup_32.c b/arch/powerpc/kernel/ 
> > setup_32.c
> > --- a/arch/powerpc/kernel/setup_32.c
> > +++ b/arch/powerpc/kernel/setup_32.c
> > @@ -132,6 +132,10 @@ void __init machine_init(unsigned long d
> >  	if (cpu_has_feature(CPU_FTR_CAN_DOZE) ||
> >  	    cpu_has_feature(CPU_FTR_CAN_NAP))
> >  		ppc_md.power_save = ppc6xx_idle;
> > +#endif
> > +
> > +#ifdef CONFIG_4xx
> > +	ppc_md.power_save = ppc4xx_idle;
> >  #endif
> >
> >  	if (ppc_md.progress)
> > diff --git a/include/asm-powerpc/machdep.h b/include/asm-powerpc/ 
> > machdep.h
> > --- a/include/asm-powerpc/machdep.h
> > +++ b/include/asm-powerpc/machdep.h
> > @@ -266,6 +266,7 @@ extern void power4_idle(void);
> >  extern void power4_idle(void);
> >  extern void power4_cpu_offline_powersave(void);
> >  extern void ppc6xx_idle(void);
> > +extern void ppc4xx_idle(void);
> >
> >  /*
> >   * ppc_md contains a copy of the machine description structure for  
> > the
> >
> > ---------------------------------------------------------------------- 
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