Subject: Re: [PATCH v2 1/5] powerpc: Move idle_loop_prolog()/epilog() functions to header file

From: Gautham R Shenoy <[email-masked]>
Date: Mon, 24 Feb 2020 10:25:06 +0530

Hello Nathan,

On Fri, Feb 21, 2020 at 09:03:16AM -0600, Nathan Lynch wrote:
> "Gautham R. Shenoy" <[email-masked]> writes:
> 
> > From: "Gautham R. Shenoy" <[email-masked]>
> >
> > Currently prior to entering an idle state on a Linux Guest, the
> > pseries cpuidle driver implement an idle_loop_prolog() and
> > idle_loop_epilog() functions which ensure that idle_purr is correctly
> > computed, and the hypervisor is informed that the CPU cycles have been
> > donated.
> >
> > These prolog and epilog functions are also required in the default
> > idle call, i.e pseries_lpar_idle(). Hence move these accessor
> > functions to a common header file and call them from
> > pseries_lpar_idle(). Since the existing header files such as
> > asm/processor.h have enough clutter, create a new header file
> > asm/idle.h.
> >
> > Signed-off-by: Gautham R. Shenoy <[email-masked]>
> > ---
> >  arch/powerpc/include/asm/idle.h        | 27 +++++++++++++++++++++++++++
> >  arch/powerpc/platforms/pseries/setup.c |  7 +++++--
> >  drivers/cpuidle/cpuidle-pseries.c      | 24 +-----------------------
> >  3 files changed, 33 insertions(+), 25 deletions(-)
> >  create mode 100644 arch/powerpc/include/asm/idle.h
> >
> > diff --git a/arch/powerpc/include/asm/idle.h b/arch/powerpc/include/asm/idle.h
> > new file mode 100644
> > index 0000000..f32a7d8
> > --- /dev/null
> > +++ b/arch/powerpc/include/asm/idle.h
> > @@ -0,0 +1,27 @@
> > +#ifndef _ASM_POWERPC_IDLE_H
> > +#define _ASM_POWERPC_IDLE_H
> > +#include <asm/runlatch.h>
> > +
> > +static inline void idle_loop_prolog(unsigned long *in_purr)
> > +{
> > +	ppc64_runlatch_off();
> > +	*in_purr = mfspr(SPRN_PURR);
> > +	/*
> > +	 * Indicate to the HV that we are idle. Now would be
> > +	 * a good time to find other work to dispatch.
> > +	 */
> > +	get_lppaca()->idle = 1;
> > +}
> > +
> > +static inline void idle_loop_epilog(unsigned long in_purr)
> > +{
> > +	u64 wait_cycles;
> > +
> > +	wait_cycles = be64_to_cpu(get_lppaca()->wait_state_cycles);
> > +	wait_cycles += mfspr(SPRN_PURR) - in_purr;
> > +	get_lppaca()->wait_state_cycles = cpu_to_be64(wait_cycles);
> > +	get_lppaca()->idle = 0;
> > +
> > +	ppc64_runlatch_on();
> > +}
> > +#endif
> 
> Looks fine and correct as a cleanup, but asm/include/idle.h and
> idle_loop_prolog, idle_loop_epilog, strike me as too generic for
> pseries-specific code.

Should it be prefixed with pseries , i.e pseries_idle_prolog()
and pseries_idle_epilog() ?

Also, I am planning another round of cleanup to move all the
idle-related declaration from asm/include/processor.h to
asm/include/idle.h