[patch 3/8] powerpc: cpu_idle implementation for systemsim

[Olof Johansson]

On Fri, Jan 13, 2006 at 01:41:16PM -0500, Arnd Bergmann wrote:
> The original cpu_idle hack from the systemsim git
> tree is a bit strange, because it unconditionally
> changes the native_idle function. This one instead
> introduces a new idle implementation that is only
> used on systemsim.
> 
> Signed-off-by: Arnd Bergmann <arndb at de.ibm.com>
> 
> Index: linux-2.6.16-rc/arch/powerpc/Kconfig
> ===================================================================
> --- linux-2.6.16-rc.orig/arch/powerpc/Kconfig
> +++ linux-2.6.16-rc/arch/powerpc/Kconfig
> @@ -380,6 +380,15 @@ config PPC_SYSTEMSIM
>  	  The Full system simulator is available for download from
>  	  http://www.alphaworks.ibm.com/tech/.
>  
> +config SYSTEMSIM_IDLE
> +	bool "   Optimized idle loop for systemsim"
> +	depends on PPC_SYSTEMSIM
> +	help
> +	  Selecting this option will enable an more optimized idle loop
> +	  for running on the IBM Full System Simulator that
> +	  significantly reduces the load on the host system when
> +	  simulating an idle system.

Do you really need this configured separately from the rest of
systemsim?

> +
>  config XICS
>  	depends on PPC_PSERIES
>  	bool
> Index: linux-2.6.16-rc/arch/powerpc/kernel/setup_64.c
> ===================================================================
> --- linux-2.6.16-rc.orig/arch/powerpc/kernel/setup_64.c
> +++ linux-2.6.16-rc/arch/powerpc/kernel/setup_64.c
> @@ -554,6 +554,23 @@ static void __init emergency_stack_init(
>  }
>  
>  /*
> + * Detect if we are running on top of the IBM Full System Simulator.
> + * If we are, use the optimized idle loop for that case.
> + */
> +static void __init setup_systemsim_idle(void)
> +{
> +#ifdef CONFIG_SYSTEMSIM_IDLE
> +	struct device_node *mambo_node;
> +
> +	mambo_node = of_find_node_by_path("/mambo");
> +	if (mambo_node) {
> +		ppc_md.idle_loop = systemsim_idle;
> +		of_node_put(mambo_node);
> +	}
> +#endif
> +}
> +
> +/*
>   * Called into from start_kernel, after lock_kernel has been called.
>   * Initializes bootmem, which is unsed to manage page allocation until
>   * mem_init is called.
> @@ -600,6 +617,8 @@ void __init setup_arch(char **cmdline_p)
>  
>  	ppc_md.setup_arch();
>  
> +	setup_systemsim_idle();
> +

Idle loops are generally probed and setup in the platform-specific inits
(setup_arch). Can't you do this from there too on the affected
platforms, it's only two after all. You can move the
setup_systemsim_idle() function to idle_systemsim.c to share it.

>  	/* Use the default idle loop if the platform hasn't provided one. */
>  	if (NULL == ppc_md.idle_loop) {
>  		ppc_md.idle_loop = default_idle;
> Index: linux-2.6.16-rc/include/asm-powerpc/machdep.h
> ===================================================================
> --- linux-2.6.16-rc.orig/include/asm-powerpc/machdep.h
> +++ linux-2.6.16-rc/include/asm-powerpc/machdep.h
> @@ -244,6 +244,7 @@ struct machdep_calls {
>  
>  extern void default_idle(void);
>  extern void native_idle(void);
> +extern void systemsim_idle(void);
>  
>  extern struct machdep_calls ppc_md;
>  extern char cmd_line[COMMAND_LINE_SIZE];
> Index: linux-2.6.16-rc/arch/powerpc/kernel/idle_systemsim.c
> ===================================================================
> --- /dev/null
> +++ linux-2.6.16-rc/arch/powerpc/kernel/idle_systemsim.c
> @@ -0,0 +1,35 @@
> +/*
> + * Idle daemon for the IBM Full System Simulator.
> + *
> + * Originally Written by Cort Dougan (cort at cs.nmt.edu)
> + *    Copyright (c) 2003-2006 IBM Corporation
> + *
> + * 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 <linux/sched.h>
> +#include <linux/preempt.h>
> +
> +#include <asm/systemsim.h>
> +
> +#define SIM_HALT_CODE 126
> +
> +static inline void systemsim_halt(void)
> +{
> +	callthru0(SIM_HALT_CODE);
> +}
> +
> +void systemsim_idle(void)
> +{
> +	while (1) {
> +		while (!need_resched())
> +			systemsim_halt();
> +
> +		preempt_enable_no_resched();
> +		schedule();
> +		preempt_disable();
> +	}
> +}
> Index: linux-2.6.16-rc/arch/powerpc/kernel/Makefile
> ===================================================================
> --- linux-2.6.16-rc.orig/arch/powerpc/kernel/Makefile
> +++ linux-2.6.16-rc/arch/powerpc/kernel/Makefile
> @@ -21,6 +21,7 @@ obj-$(CONFIG_PPC64)		+= setup_64.o binfm
>  obj-$(CONFIG_PPC64)		+= vdso64/
>  obj-$(CONFIG_ALTIVEC)		+= vecemu.o vector.o
>  obj-$(CONFIG_POWER4)		+= idle_power4.o
> +obj-$(CONFIG_SYSTEMSIM_IDLE)	+= idle_systemsim.o
>  obj-$(CONFIG_PPC_OF)		+= of_device.o prom_parse.o
>  procfs-$(CONFIG_PPC64)		:= proc_ppc64.o
>  obj-$(CONFIG_PROC_FS)		+= $(procfs-y)
> 
> --
> 
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