Subject: Re: [RFC PATCH V1 5/7] cpuidle: (POWER) cpuidle driver for pSeries

From: Benjamin Herrenschmidt <[email-masked]>
Date: Fri, 17 Jun 2011 14:36:38 +1000

On Tue, 2011-06-07 at 22:00 +0530, Trinabh Gupta wrote:

> +static int snooze_loop(struct cpuidle_device *dev,
> +			struct cpuidle_driver *drv,
> +			int index)
> +{
> +	unsigned long in_purr, out_purr;
> +	ktime_t kt_before, kt_after;
> +	s64 usec_delta;
> +
> +	/*
> +	 * Indicate to the HV that we are idle. Now would be
> +	 * a good time to find other work to dispatch.
> +	 */
> +	get_lppaca()->idle = 1;
> +	get_lppaca()->donate_dedicated_cpu = 1;
> +	in_purr = mfspr(SPRN_PURR);
> +
> +	kt_before = ktime_get_real();

Don't you want to timestamp before you tell the HV that you are idle ?
Or is the above stuff only polled by phyp when partition interrupts are
enabled ?

> +	local_irq_enable();
> +	set_thread_flag(TIF_POLLING_NRFLAG);
> +	while (!need_resched()) {
> +		ppc64_runlatch_off();
> +		HMT_low();
> +		HMT_very_low();
> +	}
> +	HMT_medium();
> +	clear_thread_flag(TIF_POLLING_NRFLAG);
> +	smp_mb();
> +	local_irq_disable();
> +
> +	kt_after = ktime_get_real();
> +	usec_delta = ktime_to_us(ktime_sub(kt_after, kt_before));
> +
> +	out_purr = mfspr(SPRN_PURR);
> +	get_lppaca()->wait_state_cycles += out_purr - in_purr;
> +	get_lppaca()->donate_dedicated_cpu = 0;
> +	get_lppaca()->idle = 0;
> +
> +	dev->last_residency = (int)usec_delta;
> +
> +	return index;
> +}
> +
> +static int dedicated_cede_loop(struct cpuidle_device *dev,
> +				struct cpuidle_driver *drv,
> +				int index)
> +{
> +	unsigned long in_purr, out_purr;
> +	ktime_t kt_before, kt_after;
> +	s64 usec_delta;
> +
> +	/*
> +	 * Indicate to the HV that we are idle. Now would be
> +	 * a good time to find other work to dispatch.
> +	 */
> +	get_lppaca()->idle = 1;
> +	get_lppaca()->donate_dedicated_cpu = 1;
> +	in_purr = mfspr(SPRN_PURR);
> +
> +	kt_before = ktime_get_real();

There's a bit too much code duplication for my taste here between the
two functions. Not sure if it can be helped, maybe with some inlines
for the prolog/epilogue ... Looks like stuff that's easy to "fix" in one
place and forget the other...

> +	ppc64_runlatch_off();
> +	HMT_medium();
> +	cede_processor();
> +
> +	kt_after = ktime_get_real();
> +	usec_delta = ktime_to_us(ktime_sub(kt_after, kt_before));
> +
> +	out_purr = mfspr(SPRN_PURR);
> +	get_lppaca()->wait_state_cycles += out_purr - in_purr;
> +	get_lppaca()->donate_dedicated_cpu = 0;
> +	get_lppaca()->idle = 0;
> +
> +	dev->last_residency = (int)usec_delta;
> +
> +	return index;
> +}
> +
> +static int shared_cede_loop(struct cpuidle_device *dev,
> +			struct cpuidle_driver *drv,
> +			int index)
> +{
> +	unsigned long in_purr, out_purr;
> +	ktime_t kt_before, kt_after;
> +	s64 usec_delta;
> +
> +	/*
> +	 * Indicate to the HV that we are idle. Now would be
> +	 * a good time to find other work to dispatch.
> +	 */
> +	get_lppaca()->idle = 1;
> +	get_lppaca()->donate_dedicated_cpu = 1;
> +	in_purr = mfspr(SPRN_PURR);
> +
> +	kt_before = ktime_get_real();
> +	/*
> +	 * Yield the processor to the hypervisor.  We return if
> +	 * an external interrupt occurs (which are driven prior
> +	 * to returning here) or if a prod occurs from another
> +	 * processor. When returning here, external interrupts
> +	 * are enabled.
> +	 */
> +	cede_processor();
> +
> +	kt_after = ktime_get_real();
> +
> +	usec_delta = ktime_to_us(ktime_sub(kt_after, kt_before));
> +
> +	out_purr = mfspr(SPRN_PURR);
> +	get_lppaca()->wait_state_cycles += out_purr - in_purr;
> +	get_lppaca()->donate_dedicated_cpu = 0;
> +	get_lppaca()->idle = 0;
> +
> +	dev->last_residency = (int)usec_delta;
> +
> +	return index;
> +}
> +
> +/*
> + * States for dedicated partition case.
> + */
> +static struct cpuidle_state dedicated_states[MAX_IDLE_STATE_COUNT] = {
> +	{ /* Snooze */
> +		.name = "snooze",
> +		.desc = "snooze",
> +		.flags = CPUIDLE_FLAG_TIME_VALID,
> +		.exit_latency = 0,
> +		.target_residency = 0,
> +		.enter = &snooze_loop },
> +	{ /* CEDE */
> +		.name = "CEDE",
> +		.desc = "CEDE",
> +		.flags = CPUIDLE_FLAG_TIME_VALID,
> +		.exit_latency = 1,
> +		.target_residency = 10,
> +		.enter = &dedicated_cede_loop },
> +};
> +
> +/*
> + * States for shared partition case.
> + */
> +static struct cpuidle_state shared_states[MAX_IDLE_STATE_COUNT] = {
> +	{ /* Shared Cede */
> +		.name = "Shared Cede",
> +		.desc = "Shared Cede",
> +		.flags = CPUIDLE_FLAG_TIME_VALID,
> +		.exit_latency = 0,
> +		.target_residency = 0,
> +		.enter = &shared_cede_loop },
> +};
> +
> +int pseries_notify_cpuidle_add_cpu(int cpu)
> +{
> +	struct cpuidle_device *dev =
> +			per_cpu_ptr(pseries_idle_cpuidle_devices, cpu);
> +	if (dev && cpuidle_get_driver()) {
> +		cpuidle_disable_device(dev);
> +		cpuidle_enable_device(dev);
> +	}
> +	return 0;
> +}
> +
> +/*
> + * pseries_idle_cpuidle_driver_init()
> + */
> +static int pseries_idle_cpuidle_driver_init(void)
> +{
> +	int cstate;
> +	struct cpuidle_driver *drv = &pseries_idle_driver;
> +
> +	drv->state_count = 0;
> +
> +	for (cstate = 0; cstate < MAX_IDLE_STATE_COUNT; ++cstate) {
> +
> +		if (cstate > max_cstate)
> +			break;
> +
> +		/* is the state not enabled? */
> +		if (cpuidle_state_table[cstate].enter == NULL)
> +			continue;
> +
> +		drv->states[drv->state_count] =	/* structure copy */
> +			cpuidle_state_table[cstate];
> +
> +		if (cpuidle_state_table == dedicated_states)
> +			drv->states[drv->state_count].target_residency =
> +				__get_cpu_var(smt_snooze_delay);
> +
> +		drv->state_count += 1;
> +	}
> +
> +	return 0;
> +}
> +
> +/* pseries_idle_devices_uninit(void)
> + * unregister cpuidle devices and de-allocate memory
> + */
> +static void pseries_idle_devices_uninit(void)
> +{
> +	int i;
> +	struct cpuidle_device *dev;
> +
> +	for_each_possible_cpu(i) {
> +		dev = per_cpu_ptr(pseries_idle_cpuidle_devices, i);
> +		cpuidle_unregister_device(dev);
> +	}
> +
> +	free_percpu(pseries_idle_cpuidle_devices);
> +	return;
> +}
> +
> +/* pseries_idle_devices_init()
> + * allocate, initialize and register cpuidle device
> + */
> +static int pseries_idle_devices_init(void)
> +{
> +	int i;
> +	struct cpuidle_driver *drv = &pseries_idle_driver;
> +	struct cpuidle_device *dev;
> +
> +	pseries_idle_cpuidle_devices = alloc_percpu(struct cpuidle_device);
> +	if (pseries_idle_cpuidle_devices == NULL)
> +		return -ENOMEM;
> +
> +	for_each_possible_cpu(i) {
> +		dev = per_cpu_ptr(pseries_idle_cpuidle_devices, i);
> +		dev->state_count = drv->state_count;
> +		dev->cpu = i;
> +		if (cpuidle_register_device(dev)) {
> +			printk(KERN_DEBUG "cpuidle_register_device %d failed!\n",
> +				 i);
> +			return -EIO;
> +		}
> +	}
> +
> +	return 0;
> +}
> +
> +/*
> + * pseries_idle_probe()
> + * Choose state table for shared versus dedicated partition
> + */
> +static int pseries_idle_probe(void)
> +{
> +	if (max_cstate == 0) {
> +		printk(KERN_DEBUG "pseries processor idle disabled.\n");
> +		return -EPERM;
> +	}
> +
> +	if (!firmware_has_feature(FW_FEATURE_SPLPAR)) {
> +		printk(KERN_DEBUG "Using default idle\n");
> +		return -ENODEV;
> +	}
> +
> +	if (get_lppaca()->shared_proc)
> +		cpuidle_state_table = shared_states;
> +	else
> +		cpuidle_state_table = dedicated_states;
> +
> +	return 0;
> +}
> +
> +static int __init pseries_processor_idle_init(void)
> +{
> +	int retval;
> +
> +	retval = pseries_idle_probe();
> +	if (retval)
> +		return retval;
> +
> +	pseries_idle_cpuidle_driver_init();
> +	retval = cpuidle_register_driver(&pseries_idle_driver);
> +	if (retval) {
> +		printk(KERN_DEBUG "Registration of pseries driver failed.\n");
> +		return retval;
> +	}
> +
> +	retval = pseries_idle_devices_init();
> +	if (retval) {
> +		pseries_idle_devices_uninit();
> +		cpuidle_unregister_driver(&pseries_idle_driver);
> +		return retval;
> +	}
> +
> +	printk(KERN_DEBUG "pseries_idle_driver registered\n");
> +
> +	return 0;
> +}
> +
> +device_initcall(pseries_processor_idle_init);
> diff --git a/arch/powerpc/platforms/pseries/pseries.h b/arch/powerpc/platforms/pseries/pseries.h
> index e9f6d28..7c60380 100644
> --- a/arch/powerpc/platforms/pseries/pseries.h
> +++ b/arch/powerpc/platforms/pseries/pseries.h
> @@ -56,4 +56,7 @@ extern struct device_node *dlpar_configure_connector(u32);
>  extern int dlpar_attach_node(struct device_node *);
>  extern int dlpar_detach_node(struct device_node *);
>  
> +/* Snooze Delay, pseries_idle */
> +DECLARE_PER_CPU(long, smt_snooze_delay);
> +
>  #endif /* _PSERIES_PSERIES_H */
> diff --git a/arch/powerpc/platforms/pseries/setup.c b/arch/powerpc/platforms/pseries/setup.c
> index 593acce..6893a0c 100644
> --- a/arch/powerpc/platforms/pseries/setup.c
> +++ b/arch/powerpc/platforms/pseries/setup.c
> @@ -584,9 +584,6 @@ static int __init pSeries_probe(void)
>  	return 1;
>  }
>  
> -
> -DECLARE_PER_CPU(long, smt_snooze_delay);
> -
>  static void pseries_dedicated_idle_sleep(void)
>  { 
>  	unsigned int cpu = smp_processor_id();
> diff --git a/arch/powerpc/platforms/pseries/smp.c b/arch/powerpc/platforms/pseries/smp.c
> index fbffd7e..2e46883 100644
> --- a/arch/powerpc/platforms/pseries/smp.c
> +++ b/arch/powerpc/platforms/pseries/smp.c
> @@ -150,6 +150,7 @@ static void __devinit smp_xics_setup_cpu(int cpu)
>  	set_cpu_current_state(cpu, CPU_STATE_ONLINE);
>  	set_default_offline_state(cpu);
>  #endif
> +	pseries_notify_cpuidle_add_cpu(cpu);
>  }
>  
>  static int __devinit smp_pSeries_kick_cpu(int nr)
> 
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