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oprofile: Implement performance counter multiplexing
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The number of hardware counters is limited. The multiplexing feature
enables OProfile to gather more events than counters are provided by
the hardware. This is realized by switching between events at an user
specified time interval.

A new file (/dev/oprofile/time_slice) is added for the user to specify
the timer interval in ms. If the number of events to profile is higher
than the number of hardware counters available, the patch will
schedule a work queue that switches the event counter and re-writes
the different sets of values into it. The switching mechanism needs to
be implemented for each architecture to support multiplexing. This
patch only implements AMD CPU support, but multiplexing can be easily
extended for other models and architectures.

There are follow-on patches that rework parts of this patch.

Signed-off-by: Jason Yeh <[email protected]>
Signed-off-by: Robert Richter <[email protected]>
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Jason Yeh authored and Robert Richter committed Jul 20, 2009
1 parent 6e63ea4 commit 4d4036e
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Showing 12 changed files with 415 additions and 20 deletions.
12 changes: 12 additions & 0 deletions arch/Kconfig
Original file line number Diff line number Diff line change
Expand Up @@ -30,6 +30,18 @@ config OPROFILE_IBS

If unsure, say N.

config OPROFILE_EVENT_MULTIPLEX
bool "OProfile multiplexing support (EXPERIMENTAL)"
default n
depends on OPROFILE && X86
help
The number of hardware counters is limited. The multiplexing
feature enables OProfile to gather more events than counters
are provided by the hardware. This is realized by switching
between events at an user specified time interval.

If unsure, say N.

config HAVE_OPROFILE
bool

Expand Down
162 changes: 157 additions & 5 deletions arch/x86/oprofile/nmi_int.c
Original file line number Diff line number Diff line change
@@ -1,11 +1,14 @@
/**
* @file nmi_int.c
*
* @remark Copyright 2002-2008 OProfile authors
* @remark Copyright 2002-2009 OProfile authors
* @remark Read the file COPYING
*
* @author John Levon <[email protected]>
* @author Robert Richter <[email protected]>
* @author Barry Kasindorf <[email protected]>
* @author Jason Yeh <[email protected]>
* @author Suravee Suthikulpanit <[email protected]>
*/

#include <linux/init.h>
Expand All @@ -24,13 +27,26 @@
#include "op_counter.h"
#include "op_x86_model.h"


#ifdef CONFIG_OPROFILE_EVENT_MULTIPLEX
DEFINE_PER_CPU(int, switch_index);
#endif


static struct op_x86_model_spec const *model;
static DEFINE_PER_CPU(struct op_msrs, cpu_msrs);
static DEFINE_PER_CPU(unsigned long, saved_lvtpc);

/* 0 == registered but off, 1 == registered and on */
static int nmi_enabled = 0;


#ifdef CONFIG_OPROFILE_EVENT_MULTIPLEX
extern atomic_t multiplex_counter;
#endif

struct op_counter_config counter_config[OP_MAX_COUNTER];

/* common functions */

u64 op_x86_get_ctrl(struct op_x86_model_spec const *model,
Expand Down Expand Up @@ -95,6 +111,11 @@ static void free_msrs(void)
per_cpu(cpu_msrs, i).counters = NULL;
kfree(per_cpu(cpu_msrs, i).controls);
per_cpu(cpu_msrs, i).controls = NULL;

#ifdef CONFIG_OPROFILE_EVENT_MULTIPLEX
kfree(per_cpu(cpu_msrs, i).multiplex);
per_cpu(cpu_msrs, i).multiplex = NULL;
#endif
}
}

Expand All @@ -103,6 +124,9 @@ static int allocate_msrs(void)
int success = 1;
size_t controls_size = sizeof(struct op_msr) * model->num_controls;
size_t counters_size = sizeof(struct op_msr) * model->num_counters;
#ifdef CONFIG_OPROFILE_EVENT_MULTIPLEX
size_t multiplex_size = sizeof(struct op_msr) * model->num_virt_counters;
#endif

int i;
for_each_possible_cpu(i) {
Expand All @@ -118,6 +142,14 @@ static int allocate_msrs(void)
success = 0;
break;
}
#ifdef CONFIG_OPROFILE_EVENT_MULTIPLEX
per_cpu(cpu_msrs, i).multiplex =
kmalloc(multiplex_size, GFP_KERNEL);
if (!per_cpu(cpu_msrs, i).multiplex) {
success = 0;
break;
}
#endif
}

if (!success)
Expand All @@ -126,13 +158,35 @@ static int allocate_msrs(void)
return success;
}

#ifdef CONFIG_OPROFILE_EVENT_MULTIPLEX

static void nmi_setup_cpu_mux(struct op_msrs const * const msrs)
{
int i;
struct op_msr *multiplex = msrs->multiplex;

for (i = 0; i < model->num_virt_counters; ++i) {
if (counter_config[i].enabled) {
multiplex[i].saved = -(u64)counter_config[i].count;
} else {
multiplex[i].addr = 0;
multiplex[i].saved = 0;
}
}
}

#endif

static void nmi_cpu_setup(void *dummy)
{
int cpu = smp_processor_id();
struct op_msrs *msrs = &per_cpu(cpu_msrs, cpu);
nmi_cpu_save_registers(msrs);
spin_lock(&oprofilefs_lock);
model->setup_ctrs(model, msrs);
#ifdef CONFIG_OPROFILE_EVENT_MULTIPLEX
nmi_setup_cpu_mux(msrs);
#endif
spin_unlock(&oprofilefs_lock);
per_cpu(saved_lvtpc, cpu) = apic_read(APIC_LVTPC);
apic_write(APIC_LVTPC, APIC_DM_NMI);
Expand Down Expand Up @@ -173,14 +227,52 @@ static int nmi_setup(void)
memcpy(per_cpu(cpu_msrs, cpu).controls,
per_cpu(cpu_msrs, 0).controls,
sizeof(struct op_msr) * model->num_controls);
#ifdef CONFIG_OPROFILE_EVENT_MULTIPLEX
memcpy(per_cpu(cpu_msrs, cpu).multiplex,
per_cpu(cpu_msrs, 0).multiplex,
sizeof(struct op_msr) * model->num_virt_counters);
#endif
}

}
on_each_cpu(nmi_cpu_setup, NULL, 1);
nmi_enabled = 1;
return 0;
}

#ifdef CONFIG_OPROFILE_EVENT_MULTIPLEX

static void nmi_cpu_save_mpx_registers(struct op_msrs *msrs)
{
unsigned int si = __get_cpu_var(switch_index);
struct op_msr *multiplex = msrs->multiplex;
unsigned int i;

for (i = 0; i < model->num_counters; ++i) {
int offset = i + si;
if (multiplex[offset].addr) {
rdmsrl(multiplex[offset].addr,
multiplex[offset].saved);
}
}
}

static void nmi_cpu_restore_mpx_registers(struct op_msrs *msrs)
{
unsigned int si = __get_cpu_var(switch_index);
struct op_msr *multiplex = msrs->multiplex;
unsigned int i;

for (i = 0; i < model->num_counters; ++i) {
int offset = i + si;
if (multiplex[offset].addr) {
wrmsrl(multiplex[offset].addr,
multiplex[offset].saved);
}
}
}

#endif

static void nmi_cpu_restore_registers(struct op_msrs *msrs)
{
struct op_msr *counters = msrs->counters;
Expand Down Expand Up @@ -214,6 +306,9 @@ static void nmi_cpu_shutdown(void *dummy)
apic_write(APIC_LVTPC, per_cpu(saved_lvtpc, cpu));
apic_write(APIC_LVTERR, v);
nmi_cpu_restore_registers(msrs);
#ifdef CONFIG_OPROFILE_EVENT_MULTIPLEX
__get_cpu_var(switch_index) = 0;
#endif
}

static void nmi_shutdown(void)
Expand Down Expand Up @@ -252,23 +347,23 @@ static void nmi_stop(void)
on_each_cpu(nmi_cpu_stop, NULL, 1);
}

struct op_counter_config counter_config[OP_MAX_COUNTER];

static int nmi_create_files(struct super_block *sb, struct dentry *root)
{
unsigned int i;

for (i = 0; i < model->num_counters; ++i) {
for (i = 0; i < model->num_virt_counters; ++i) {
struct dentry *dir;
char buf[4];

#ifndef CONFIG_OPROFILE_EVENT_MULTIPLEX
/* quick little hack to _not_ expose a counter if it is not
* available for use. This should protect userspace app.
* NOTE: assumes 1:1 mapping here (that counters are organized
* sequentially in their struct assignment).
*/
if (unlikely(!avail_to_resrv_perfctr_nmi_bit(i)))
continue;
#endif /* CONFIG_OPROFILE_EVENT_MULTIPLEX */

snprintf(buf, sizeof(buf), "%d", i);
dir = oprofilefs_mkdir(sb, root, buf);
Expand All @@ -283,6 +378,57 @@ static int nmi_create_files(struct super_block *sb, struct dentry *root)
return 0;
}

#ifdef CONFIG_OPROFILE_EVENT_MULTIPLEX

static void nmi_cpu_switch(void *dummy)
{
int cpu = smp_processor_id();
int si = per_cpu(switch_index, cpu);
struct op_msrs *msrs = &per_cpu(cpu_msrs, cpu);

nmi_cpu_stop(NULL);
nmi_cpu_save_mpx_registers(msrs);

/* move to next set */
si += model->num_counters;
if ((si > model->num_virt_counters) || (counter_config[si].count == 0))
per_cpu(switch_index, cpu) = 0;
else
per_cpu(switch_index, cpu) = si;

model->switch_ctrl(model, msrs);
nmi_cpu_restore_mpx_registers(msrs);

nmi_cpu_start(NULL);
}


/*
* Quick check to see if multiplexing is necessary.
* The check should be sufficient since counters are used
* in ordre.
*/
static int nmi_multiplex_on(void)
{
return counter_config[model->num_counters].count ? 0 : -EINVAL;
}

static int nmi_switch_event(void)
{
if (!model->switch_ctrl)
return -ENOSYS; /* not implemented */
if (nmi_multiplex_on() < 0)
return -EINVAL; /* not necessary */

on_each_cpu(nmi_cpu_switch, NULL, 1);

atomic_inc(&multiplex_counter);

return 0;
}

#endif

#ifdef CONFIG_SMP
static int oprofile_cpu_notifier(struct notifier_block *b, unsigned long action,
void *data)
Expand Down Expand Up @@ -516,12 +662,18 @@ int __init op_nmi_init(struct oprofile_operations *ops)
register_cpu_notifier(&oprofile_cpu_nb);
#endif
/* default values, can be overwritten by model */
#ifdef CONFIG_OPROFILE_EVENT_MULTIPLEX
__raw_get_cpu_var(switch_index) = 0;
#endif
ops->create_files = nmi_create_files;
ops->setup = nmi_setup;
ops->shutdown = nmi_shutdown;
ops->start = nmi_start;
ops->stop = nmi_stop;
ops->cpu_type = cpu_type;
#ifdef CONFIG_OPROFILE_EVENT_MULTIPLEX
ops->switch_events = nmi_switch_event;
#endif

if (model->init)
ret = model->init(ops);
Expand Down
2 changes: 1 addition & 1 deletion arch/x86/oprofile/op_counter.h
Original file line number Diff line number Diff line change
Expand Up @@ -10,7 +10,7 @@
#ifndef OP_COUNTER_H
#define OP_COUNTER_H

#define OP_MAX_COUNTER 8
#define OP_MAX_COUNTER 32

/* Per-perfctr configuration as set via
* oprofilefs.
Expand Down
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