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

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Message-ID: <87lfowt22z.fsf@linux.ibm.com>
Date:   Fri, 21 Feb 2020 09:03:16 -0600
From:   Nathan Lynch <nathanl@...ux.ibm.com>
To:     "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        Michael Ellerman <mpe@...erman.id.au>,
        Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
        Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
        "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        Tyrel Datwyler <tyreld@...ux.ibm.com>
Subject: Re: [PATCH v2 1/5] powerpc: Move idle_loop_prolog()/epilog() functions to header file

"Gautham R. Shenoy" <ego@...ux.vnet.ibm.com> writes:

> From: "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>
>
> 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 <ego@...ux.vnet.ibm.com>
> ---
>  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.