Subject: Re: [PATCH v3 2/2] powerpc: add support for new hcall H_BEST_ENERGY

From: Vaidyanathan Srinivasan <[email-masked]>
Date: Mon, 28 Jun 2010 11:03:24 +0530

* Michael Neuling <[email-masked]> [2010-06-28 11:44:31]:

> Vaidy,
> 
> > 	Create sysfs interface to export data from H_BEST_ENERGY hcall
> > 	that can be used by administrative tools on supported pseries
> > 	platforms for energy management	optimizations.
> > 
> > 	/sys/device/system/cpu/pseries_(de)activate_hint_list and
> > 	/sys/device/system/cpu/cpuN/pseries_(de)activate_hint will provide
> > 	hints for activation and deactivation of cpus respectively.
> > 
> > 	Added new driver module
> > 		arch/powerpc/platforms/pseries/pseries_energy.c
> > 	under new config option CONFIG_PSERIES_ENERGY
> 
> Can you provide some documentation on how to use these hints and what
> format they are provided from sysfs.  Looks like two separate interfaces
> two the same thing (one a comma sep list and 1 per cpu, why do need
> both?).  What is the difference between activate and deactivate, with
> out me having to read PAPR :-) ??

Hi Mike,

Thanks for reviewing this patch series.  Sure, I can provide
additional information.

These hints are abstract number given by the hypervisor based on
the extended knowledge the hypervisor has regarding the current system
topology and resource mappings.

The activate and the deactivate part is for the two distinct
operations that we could do for energy savings.  When we have more
capacity than required, we could deactivate few core to save energy.
The choice of the core to deactivate will be based on
/sys/devices/system/cpu/deactivate_hint_list.  The comma separated
list of cpus (cores) will be the preferred choice.

Once the system has few deactivated cores, based on workload demand we
may have to activate them to meet the demand.  In that case the
/sys/devices/system/cpu/activate_hint_list will be used to prefer the
core in-order among the deactivated cores.

In simple terms, activate_hint_list will be null until we deactivate
few cores.  Then we could look at the corresponding list for
activation or deactivation.

Regarding your second point, there is a reason for both a list and
per-cpu interface.  The list gives us a system wide list of cores in
one shot for userspace to base their decision.  This will be the
preferred interface for most cases.  On the other hand, per-cpu file
/sys/device/system/cpu/cpuN/pseries_(de)activate_hint provide more
information since it exports the hint value as such.

The idea is that the list interface will be used to get a suggested
list of cores to manage, while the per-cpu value can be used to
further get fine grain information on a per-core bases from the
hypervisor.  This allows Linux to have access to all information that
the hypervisor has offered through this hcall interface.

> Other comments below.
> 
> > 
> > Signed-off-by: Vaidyanathan Srinivasan <[email-masked]>
> > ---
> >  arch/powerpc/include/asm/hvcall.h               |    3 
> >  arch/powerpc/platforms/pseries/Kconfig          |   10 +
> >  arch/powerpc/platforms/pseries/Makefile         |    1 
> >  arch/powerpc/platforms/pseries/pseries_energy.c |  258 +++++++++++++++++++++
> ++
> >  4 files changed, 271 insertions(+), 1 deletions(-)
> >  create mode 100644 arch/powerpc/platforms/pseries/pseries_energy.c
> > 
> > diff --git a/arch/powerpc/include/asm/hvcall.h b/arch/powerpc/include/asm/hvc
> all.h
> > index 5119b7d..34b66e0 100644
> > --- a/arch/powerpc/include/asm/hvcall.h
> > +++ b/arch/powerpc/include/asm/hvcall.h
> > @@ -231,7 +231,8 @@
> >  #define H_GET_EM_PARMS		0x2B8
> >  #define H_SET_MPP		0x2D0
> >  #define H_GET_MPP		0x2D4
> > -#define MAX_HCALL_OPCODE	H_GET_MPP
> > +#define H_BEST_ENERGY		0x2F4
> > +#define MAX_HCALL_OPCODE	H_BEST_ENERGY
> > 
> >  #ifndef __ASSEMBLY__
> > 
> > diff --git a/arch/powerpc/platforms/pseries/Kconfig b/arch/powerpc/platforms/
> pseries/Kconfig
> > index c667f0f..b3dd108 100644
> > --- a/arch/powerpc/platforms/pseries/Kconfig
> > +++ b/arch/powerpc/platforms/pseries/Kconfig
> > @@ -33,6 +33,16 @@ config PSERIES_MSI
> >         depends on PCI_MSI && EEH
> >         default y
> > 
> > +config PSERIES_ENERGY
> 
> Probably need a less generic name.  PSERIES_ENERGY_MANAGEMENT?
> PSERIES_ENERGY_HOTPLUG_HINTS?

PSERIES_ENERGY_MANAGEMENT may be good but too long for a config
option.

The idea is to collect all energy management functions in this module
as and when new features are introduced in the pseries platform.  This
hcall interface is the first to be included, but going forward in
future I do not propose to have different modules for other energy
management related features.

The name is specific enough for IBM pseries platform and energy
management functions and enablements.  Having less generic name below
this level will make it difficult to add all varieties of energy
management functions in future.

> > +	tristate "pseries energy management capabilities driver"
> > +	depends on PPC_PSERIES
> > +	default y
> > +	help
> > +	  Provides interface to platform energy management capabilities
> > +	  on supported PSERIES platforms.
> > +	  Provides: /sys/devices/system/cpu/pseries_(de)activation_hint_list
> > +	  and /sys/devices/system/cpu/cpuN/pseries_(de)activation_hint
> > +
> >  config SCANLOG
> >  	tristate "Scanlog dump interface"
> >  	depends on RTAS_PROC && PPC_PSERIES
> > diff --git a/arch/powerpc/platforms/pseries/Makefile b/arch/powerpc/platforms
> /pseries/Makefile
> > index 3dbef30..32ae72e 100644
> > --- a/arch/powerpc/platforms/pseries/Makefile
> > +++ b/arch/powerpc/platforms/pseries/Makefile
> > @@ -16,6 +16,7 @@ obj-$(CONFIG_EEH)	+= eeh.o eeh_cache.o eeh_driver.o eeh_e
> vent.o eeh_sysfs.o
> >  obj-$(CONFIG_KEXEC)	+= kexec.o
> >  obj-$(CONFIG_PCI)	+= pci.o pci_dlpar.o
> >  obj-$(CONFIG_PSERIES_MSI)	+= msi.o
> > +obj-$(CONFIG_PSERIES_ENERGY)	+= pseries_energy.o
> > 
> >  obj-$(CONFIG_HOTPLUG_CPU)	+= hotplug-cpu.o
> >  obj-$(CONFIG_MEMORY_HOTPLUG)	+= hotplug-memory.o
> > diff --git a/arch/powerpc/platforms/pseries/pseries_energy.c b/arch/powerpc/p
> latforms/pseries/pseries_energy.c
> > new file mode 100644
> > index 0000000..9a936b1
> > --- /dev/null
> > +++ b/arch/powerpc/platforms/pseries/pseries_energy.c
> > @@ -0,0 +1,258 @@
> > +/*
> > + * POWER platform energy management driver
> > + * Copyright (C) 2010 IBM Corporation
> > + *
> > + * This program is free software; you can redistribute it and/or
> > + * modify it under the terms of the GNU General Public License
> > + * version 2 as published by the Free Software Foundation.
> > + *
> > + * This pseries platform device driver provides access to
> > + * platform energy management capabilities.
> > + */
> > +
> > +#include <linux/module.h>
> > +#include <linux/types.h>
> > +#include <linux/errno.h>
> > +#include <linux/init.h>
> > +#include <linux/seq_file.h>
> > +#include <linux/sysdev.h>
> > +#include <linux/cpu.h>
> > +#include <linux/of.h>
> > +#include <asm/cputhreads.h>
> > +#include <asm/page.h>
> > +#include <asm/hvcall.h>
> > +
> > +
> > +#define MODULE_VERS "1.0"
> 
> Argh, I hate module versions... but this one is less of an issue since
> it doesn't seem to be being used anyway :-)
> 
> > +#define MODULE_NAME "pseries_energy"
> 
> Unused too.

Yes.  This keep the module template complete.  No overhead as yet :)
We will certainly need the MODULE_VERS in future if we add/change
sysfs interfaces.

> > +
> > +/* Helper Routines to convert between drc_index to cpu numbers */
> > +
> > +static u32 cpu_to_drc_index(int cpu)
> > +{
> > +	struct device_node *dn = NULL;
> > +	const int *indexes;
> > +	int i;
> > +	dn = of_find_node_by_path("/cpus");
> > +	if (dn == NULL)
> > +		goto err;
> 
> Humm, I not sure this is really needed.  If you don't have /cpus you are
> probably not going to boot.

Good suggestion.  I could add all these checks in module_init.   I was
think if any of the functions being called is allocating memory and in
case they fail, we need to abort.

I just reviewed and look like of_find_node_by_path() will not sleep or
allocate any memory.  So if it succeeds once in module_init(), then it
will never fail! 

> > +	indexes = of_get_property(dn, "ibm,drc-indexes", NULL);
> > +	if (indexes == NULL)
> > +		goto err;
> 
> These checks should probably be moved to module init rather than /sfs
> read time.  If they fail, don't load the module and print a warning.  
> 
> These HCALLS and device-tree entire aren't going to be dynamic.

Agreed.  Only cause of runtime failure is OOM.  If none of these
allocate memory, moving these checks once at module_init() will be
a good optimization.

But still I am wondering if it is worth the risk.  These are not in
hot paths and these are just quick null comparisons.  Also in most other
call sites, we do check for return values.

> > +	/* Convert logical cpu number to core number */
> > +	i = cpu_core_of_thread(cpu);
> > +	/*
> > +	 * The first element indexes[0] is the number of drc_indexes
> > +	 * returned in the list.  Hence i+1 will get the drc_index
> > +	 * corresponding to core number i.
> > +	 */
> > +	WARN_ON(i > indexes[0]);
> > +	return indexes[i + 1];
> > +err:
> > +	printk(KERN_WARNING "cpu_to_drc_index(%d) failed", cpu);
> > +	return 0;
> > +}
> > +
> > +static int drc_index_to_cpu(u32 drc_index)
> > +{
> > +	struct device_node *dn = NULL;
> > +	const int *indexes;
> > +	int i, cpu;
> > +	dn = of_find_node_by_path("/cpus");
> > +	if (dn == NULL)
> > +		goto err;
> 
> same here

agreed, comments mentioned above.

> > +	indexes = of_get_property(dn, "ibm,drc-indexes", NULL);
> > +	if (indexes == NULL)
> > +		goto err;
> > +	/*
> > +	 * First element in the array is the number of drc_indexes
> > +	 * returned.  Search through the list to find the matching
> > +	 * drc_index and get the core number
> > +	 */
> > +	for (i = 0; i < indexes[0]; i++) {
> > +		if (indexes[i + 1] == drc_index)
> > +			break;
> > +	}
> > +	/* Convert core number to logical cpu number */
> > +	cpu = cpu_first_thread_of_core(i);
> > +	return cpu;
> > +err:
> > +	printk(KERN_WARNING "drc_index_to_cpu(%d) failed", drc_index);
> > +	return 0;
> > +}
> > +
> > +/*
> > + * pseries hypervisor call H_BEST_ENERGY provides hints to OS on
> > + * preferred logical cpus to activate or deactivate for optimized
> > + * energy consumption.
> > + */
> > +
> > +#define FLAGS_MODE1	0x004E200000080E01
> > +#define FLAGS_MODE2	0x004E200000080401
> > +#define FLAGS_ACTIVATE  0x100
> > +
> > +static ssize_t get_best_energy_list(char *page, int activate)
> > +{
> > +	int rc, cnt, i, cpu;
> > +	unsigned long retbuf[PLPAR_HCALL9_BUFSIZE];
> > +	unsigned long flags = 0;
> > +	u32 *buf_page;
> > +	char *s = page;
> > +
> > +	buf_page = (u32 *) get_zeroed_page(GFP_KERNEL);
> > +	if (!buf_page)
> > +		return -ENOMEM;
> > +
> > +	flags = FLAGS_MODE1;
> > +	if (activate)
> > +		flags |= FLAGS_ACTIVATE;
> > +
> > +	rc = plpar_hcall9(H_BEST_ENERGY, retbuf, flags, 0, __pa(buf_page),
> > +				0, 0, 0, 0, 0, 0);
> > +	if (rc != H_SUCCESS) {
> > +		free_page((unsigned long) buf_page);
> > +		return -EINVAL;
> > +	}
> > +
> > +	cnt = retbuf[0];
> > +	for (i = 0; i < cnt; i++) {
> > +		cpu = drc_index_to_cpu(buf_page[2*i+1]);
> > +		if ((cpu_online(cpu) && !activate) ||
> > +		    (!cpu_online(cpu) && activate))
> > +			s += sprintf(s, "%d,", cpu);
> > +	}
> > +	if (s > page) { /* Something to show */
> > +		s--; /* Suppress last comma */
> > +		s += sprintf(s, "\n");
> > +	}
> > +
> > +	free_page((unsigned long) buf_page);
> > +	return s-page;
> > +}
> > +
> > +static ssize_t get_best_energy_data(struct sys_device *dev,
> > +					char *page, int activate)
> > +{
> > +	int rc;
> > +	unsigned long retbuf[PLPAR_HCALL9_BUFSIZE];
> > +	unsigned long flags = 0;
> > +
> > +	flags = FLAGS_MODE2;
> > +	if (activate)
> > +		flags |= FLAGS_ACTIVATE;
> > +
> > +	rc = plpar_hcall9(H_BEST_ENERGY, retbuf, flags,
> > +				cpu_to_drc_index(dev->id),
> > +				0, 0, 0, 0, 0, 0, 0);
> > +
> > +	if (rc != H_SUCCESS)
> > +		return -EINVAL;
> > +
> > +	return sprintf(page, "%lu\n", retbuf[1] >> 32);
> > +}
> > +
> > +/* Wrapper functions */
> > +
> > +static ssize_t cpu_activate_hint_list_show(struct sysdev_class *class,
> > +			struct sysdev_class_attribute *attr, char *page)
> > +{
> > +	return get_best_energy_list(page, 1);
> > +}
> > +
> > +static ssize_t cpu_deactivate_hint_list_show(struct sysdev_class *class,
> > +			struct sysdev_class_attribute *attr, char *page)
> > +{
> > +	return get_best_energy_list(page, 0);
> > +}
> > +
> > +static ssize_t percpu_activate_hint_show(struct sys_device *dev,
> > +			struct sysdev_attribute *attr, char *page)
> > +{
> > +	return get_best_energy_data(dev, page, 1);
> > +}
> > +
> > +static ssize_t percpu_deactivate_hint_show(struct sys_device *dev,
> > +			struct sysdev_attribute *attr, char *page)
> > +{
> > +	return get_best_energy_data(dev, page, 0);
> > +}
> > +
> > +/*
> > + * Create sysfs interface:
> > + * /sys/devices/system/cpu/pseries_activate_hint_list
> > + * /sys/devices/system/cpu/pseries_deactivate_hint_list
> > + * 	Comma separated list of cpus to activate or deactivate
> > + * /sys/devices/system/cpu/cpuN/pseries_activate_hint
> > + * /sys/devices/system/cpu/cpuN/pseries_deactivate_hint
> > + *	Per-cpu value of the hint
> 
> Do we really need both interfaces?  Seems like awk could generate one
> from the other in userspace?

Yes, it is possible, but will not scale.  Generating a list from set
of per-cpu values is possible but will be too much overhead to build
the list.  Having the list interface and deleting the per-cpu ones
will reduce information available from hypervisor.  Having both the
interface is a good balance between amount of information exported and
quick access to a consolidated view.

> > + */
> > +
> > +struct sysdev_class_attribute attr_cpu_activate_hint_list =
> > +		_SYSDEV_CLASS_ATTR(pseries_activate_hint_list, 0444,
> > +		cpu_activate_hint_list_show, NULL);
> > +
> > +struct sysdev_class_attribute attr_cpu_deactivate_hint_list =
> > +		_SYSDEV_CLASS_ATTR(pseries_deactivate_hint_list, 0444,
> > +		cpu_deactivate_hint_list_show, NULL);
> > +
> > +struct sysdev_attribute attr_percpu_activate_hint =
> > +		_SYSDEV_ATTR(pseries_activate_hint, 0444,
> > +		percpu_activate_hint_show, NULL);
> > +
> > +struct sysdev_attribute attr_percpu_deactivate_hint =
> > +		_SYSDEV_ATTR(pseries_deactivate_hint, 0444,
> > +		percpu_deactivate_hint_show, NULL);
> 
> > +
> > +static int __init pseries_energy_init(void)
> > +{
> > +	int cpu, err;
> > +	struct sys_device *cpu_sys_dev;
> > +
> > +	/* Create the sysfs files */
> > +	err = sysfs_create_file(&cpu_sysdev_class.kset.kobj,
> > +				&attr_cpu_activate_hint_list.attr);
> > +	if (!err)
> > +		err = sysfs_create_file(&cpu_sysdev_class.kset.kobj,
> > +				&attr_cpu_deactivate_hint_list.attr);
> > +
> > +	for_each_possible_cpu(cpu) {
> > +		cpu_sys_dev = get_cpu_sysdev(cpu);
> > +		err = sysfs_create_file(&cpu_sys_dev->kobj,
> > +				&attr_percpu_activate_hint.attr);
> > +		if (err)
> > +			break;
> > +		err = sysfs_create_file(&cpu_sys_dev->kobj,
> > +				&attr_percpu_deactivate_hint.attr);
> > +		if (err)
> > +			break;
> > +	}
> > +	return err;
> > +
> > +}
> > +
> > +static void __exit pseries_energy_cleanup(void)
> > +{
> > +	int cpu;
> > +	struct sys_device *cpu_sys_dev;
> > +
> > +	/* Remove the sysfs files */
> > +	sysfs_remove_file(&cpu_sysdev_class.kset.kobj,
> > +				&attr_cpu_activate_hint_list.attr);
> > +
> > +	sysfs_remove_file(&cpu_sysdev_class.kset.kobj,
> > +				&attr_cpu_deactivate_hint_list.attr);
> > +
> > +	for_each_possible_cpu(cpu) {
> > +		cpu_sys_dev = get_cpu_sysdev(cpu);
> > +		sysfs_remove_file(&cpu_sys_dev->kobj,
> > +				&attr_percpu_activate_hint.attr);
> > +		sysfs_remove_file(&cpu_sys_dev->kobj,
> > +				&attr_percpu_deactivate_hint.attr);
> > +	}
> > +}
> > +
> > +module_init(pseries_energy_init);
> > +module_exit(pseries_energy_cleanup);
> > +MODULE_DESCRIPTION("Driver for pseries platform energy management");
> 
> Needs a less generic description. 

Explained above.

Thanks,
Vaidy