[tip:perfcounters/core] perf_counter: Rework the perf counter disable/enable

From: tip-bot for Peter Zijlstra
Date: Fri May 15 2009 - 04:46:51 EST

Commit-ID: 9e35ad388bea89f7d6f375af4c0ae98803688666
Gitweb: http://git.kernel.org/tip/9e35ad388bea89f7d6f375af4c0ae98803688666
Author: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
AuthorDate: Wed, 13 May 2009 16:21:38 +0200
Committer: Ingo Molnar <mingo@xxxxxxx>
CommitDate: Fri, 15 May 2009 09:47:02 +0200

perf_counter: Rework the perf counter disable/enable

The current disable/enable mechanism is:

token = hw_perf_save_disable();
...
/* do bits */
...
hw_perf_restore(token);

This works well, provided that the use nests properly. Except we don't.

x86 NMI/INT throttling has non-nested use of this, breaking things. Therefore
provide a reference counter disable/enable interface, where the first disable
disables the hardware, and the last enable enables the hardware again.

[ Impact: refactor, simplify the PMU disable/enable logic ]

Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Cc: Corey Ashford <cjashfor@xxxxxxxxxxxxxxxxxx>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>


---
arch/powerpc/kernel/perf_counter.c | 24 ++++----
arch/x86/kernel/cpu/perf_counter.c | 113 +++++++++++++----------------------
drivers/acpi/processor_idle.c | 6 +-
include/linux/perf_counter.h | 10 ++-
kernel/perf_counter.c | 76 +++++++++++++++---------
5 files changed, 109 insertions(+), 120 deletions(-)

diff --git a/arch/powerpc/kernel/perf_counter.c b/arch/powerpc/kernel/perf_counter.c
index 15cdc8e..bb1b463 100644
--- a/arch/powerpc/kernel/perf_counter.c
+++ b/arch/powerpc/kernel/perf_counter.c
@@ -386,7 +386,7 @@ static void write_mmcr0(struct cpu_hw_counters *cpuhw, unsigned long mmcr0)
* Disable all counters to prevent PMU interrupts and to allow
* counters to be added or removed.
*/
-u64 hw_perf_save_disable(void)
+void hw_perf_disable(void)
{
struct cpu_hw_counters *cpuhw;
unsigned long ret;
@@ -428,7 +428,6 @@ u64 hw_perf_save_disable(void)
mb();
}
local_irq_restore(flags);
- return ret;
}

/*
@@ -436,7 +435,7 @@ u64 hw_perf_save_disable(void)
* If we were previously disabled and counters were added, then
* put the new config on the PMU.
*/
-void hw_perf_restore(u64 disable)
+void hw_perf_enable(void)
{
struct perf_counter *counter;
struct cpu_hw_counters *cpuhw;
@@ -448,9 +447,12 @@ void hw_perf_restore(u64 disable)
int n_lim;
int idx;

- if (disable)
- return;
local_irq_save(flags);
+ if (!cpuhw->disabled) {
+ local_irq_restore(flags);
+ return;
+ }
+
cpuhw = &__get_cpu_var(cpu_hw_counters);
cpuhw->disabled = 0;

@@ -649,19 +651,18 @@ int hw_perf_group_sched_in(struct perf_counter *group_leader,
/*
* Add a counter to the PMU.
* If all counters are not already frozen, then we disable and
- * re-enable the PMU in order to get hw_perf_restore to do the
+ * re-enable the PMU in order to get hw_perf_enable to do the
* actual work of reconfiguring the PMU.
*/
static int power_pmu_enable(struct perf_counter *counter)
{
struct cpu_hw_counters *cpuhw;
unsigned long flags;
- u64 pmudis;
int n0;
int ret = -EAGAIN;

local_irq_save(flags);
- pmudis = hw_perf_save_disable();
+ perf_disable();

/*
* Add the counter to the list (if there is room)
@@ -685,7 +686,7 @@ static int power_pmu_enable(struct perf_counter *counter)

ret = 0;
out:
- hw_perf_restore(pmudis);
+ perf_enable();
local_irq_restore(flags);
return ret;
}
@@ -697,11 +698,10 @@ static void power_pmu_disable(struct perf_counter *counter)
{
struct cpu_hw_counters *cpuhw;
long i;
- u64 pmudis;
unsigned long flags;

local_irq_save(flags);
- pmudis = hw_perf_save_disable();
+ perf_disable();

power_pmu_read(counter);

@@ -735,7 +735,7 @@ static void power_pmu_disable(struct perf_counter *counter)
cpuhw->mmcr[0] &= ~(MMCR0_PMXE | MMCR0_FCECE);
}

- hw_perf_restore(pmudis);
+ perf_enable();
local_irq_restore(flags);
}

diff --git a/arch/x86/kernel/cpu/perf_counter.c b/arch/x86/kernel/cpu/perf_counter.c
index 7601c01..313638c 100644
--- a/arch/x86/kernel/cpu/perf_counter.c
+++ b/arch/x86/kernel/cpu/perf_counter.c
@@ -31,7 +31,6 @@ struct cpu_hw_counters {
unsigned long used_mask[BITS_TO_LONGS(X86_PMC_IDX_MAX)];
unsigned long active_mask[BITS_TO_LONGS(X86_PMC_IDX_MAX)];
unsigned long interrupts;
- u64 throttle_ctrl;
int enabled;
};

@@ -42,8 +41,8 @@ struct x86_pmu {
const char *name;
int version;
int (*handle_irq)(struct pt_regs *, int);
- u64 (*save_disable_all)(void);
- void (*restore_all)(u64);
+ void (*disable_all)(void);
+ void (*enable_all)(void);
void (*enable)(struct hw_perf_counter *, int);
void (*disable)(struct hw_perf_counter *, int);
unsigned eventsel;
@@ -56,6 +55,7 @@ struct x86_pmu {
int counter_bits;
u64 counter_mask;
u64 max_period;
+ u64 intel_ctrl;
};

static struct x86_pmu x86_pmu __read_mostly;
@@ -311,22 +311,19 @@ static int __hw_perf_counter_init(struct perf_counter *counter)
return 0;
}

-static u64 intel_pmu_save_disable_all(void)
+static void intel_pmu_disable_all(void)
{
- u64 ctrl;
-
- rdmsrl(MSR_CORE_PERF_GLOBAL_CTRL, ctrl);
wrmsrl(MSR_CORE_PERF_GLOBAL_CTRL, 0);
-
- return ctrl;
}

-static u64 amd_pmu_save_disable_all(void)
+static void amd_pmu_disable_all(void)
{
struct cpu_hw_counters *cpuc = &__get_cpu_var(cpu_hw_counters);
- int enabled, idx;
+ int idx;
+
+ if (!cpuc->enabled)
+ return;

- enabled = cpuc->enabled;
cpuc->enabled = 0;
/*
* ensure we write the disable before we start disabling the
@@ -334,8 +331,6 @@ static u64 amd_pmu_save_disable_all(void)
* right thing.
*/
barrier();
- if (!enabled)
- goto out;

for (idx = 0; idx < x86_pmu.num_counters; idx++) {
u64 val;
@@ -348,37 +343,31 @@ static u64 amd_pmu_save_disable_all(void)
val &= ~ARCH_PERFMON_EVENTSEL0_ENABLE;
wrmsrl(MSR_K7_EVNTSEL0 + idx, val);
}
-
-out:
- return enabled;
}

-u64 hw_perf_save_disable(void)
+void hw_perf_disable(void)
{
if (!x86_pmu_initialized())
- return 0;
- return x86_pmu.save_disable_all();
+ return;
+ return x86_pmu.disable_all();
}
-/*
- * Exported because of ACPI idle
- */
-EXPORT_SYMBOL_GPL(hw_perf_save_disable);

-static void intel_pmu_restore_all(u64 ctrl)
+static void intel_pmu_enable_all(void)
{
- wrmsrl(MSR_CORE_PERF_GLOBAL_CTRL, ctrl);
+ wrmsrl(MSR_CORE_PERF_GLOBAL_CTRL, x86_pmu.intel_ctrl);
}

-static void amd_pmu_restore_all(u64 ctrl)
+static void amd_pmu_enable_all(void)
{
struct cpu_hw_counters *cpuc = &__get_cpu_var(cpu_hw_counters);
int idx;

- cpuc->enabled = ctrl;
- barrier();
- if (!ctrl)
+ if (cpuc->enabled)
return;

+ cpuc->enabled = 1;
+ barrier();
+
for (idx = 0; idx < x86_pmu.num_counters; idx++) {
u64 val;

@@ -392,16 +381,12 @@ static void amd_pmu_restore_all(u64 ctrl)
}
}

-void hw_perf_restore(u64 ctrl)
+void hw_perf_enable(void)
{
if (!x86_pmu_initialized())
return;
- x86_pmu.restore_all(ctrl);
+ x86_pmu.enable_all();
}
-/*
- * Exported because of ACPI idle
- */
-EXPORT_SYMBOL_GPL(hw_perf_restore);

static inline u64 intel_pmu_get_status(void)
{
@@ -735,15 +720,14 @@ static int intel_pmu_handle_irq(struct pt_regs *regs, int nmi)
int bit, cpu = smp_processor_id();
u64 ack, status;
struct cpu_hw_counters *cpuc = &per_cpu(cpu_hw_counters, cpu);
- int ret = 0;
-
- cpuc->throttle_ctrl = intel_pmu_save_disable_all();

+ perf_disable();
status = intel_pmu_get_status();
- if (!status)
- goto out;
+ if (!status) {
+ perf_enable();
+ return 0;
+ }

- ret = 1;
again:
inc_irq_stat(apic_perf_irqs);
ack = status;
@@ -767,19 +751,11 @@ again:
status = intel_pmu_get_status();
if (status)
goto again;
-out:
- /*
- * Restore - do not reenable when global enable is off or throttled:
- */
- if (cpuc->throttle_ctrl) {
- if (++cpuc->interrupts < PERFMON_MAX_INTERRUPTS) {
- intel_pmu_restore_all(cpuc->throttle_ctrl);
- } else {
- pr_info("CPU#%d: perfcounters: max interrupt rate exceeded! Throttle on.\n", smp_processor_id());
- }
- }

- return ret;
+ if (++cpuc->interrupts != PERFMON_MAX_INTERRUPTS)
+ perf_enable();
+
+ return 1;
}

static int amd_pmu_handle_irq(struct pt_regs *regs, int nmi)
@@ -792,13 +768,11 @@ static int amd_pmu_handle_irq(struct pt_regs *regs, int nmi)
struct hw_perf_counter *hwc;
int idx, throttle = 0;

- cpuc->throttle_ctrl = cpuc->enabled;
- cpuc->enabled = 0;
- barrier();
-
- if (cpuc->throttle_ctrl) {
- if (++cpuc->interrupts >= PERFMON_MAX_INTERRUPTS)
- throttle = 1;
+ if (++cpuc->interrupts == PERFMON_MAX_INTERRUPTS) {
+ throttle = 1;
+ __perf_disable();
+ cpuc->enabled = 0;
+ barrier();
}

for (idx = 0; idx < x86_pmu.num_counters; idx++) {
@@ -824,9 +798,6 @@ next:
amd_pmu_disable_counter(hwc, idx);
}

- if (cpuc->throttle_ctrl && !throttle)
- cpuc->enabled = 1;
-
return handled;
}

@@ -839,13 +810,11 @@ void perf_counter_unthrottle(void)

cpuc = &__get_cpu_var(cpu_hw_counters);
if (cpuc->interrupts >= PERFMON_MAX_INTERRUPTS) {
- pr_info("CPU#%d: perfcounters: throttle off.\n", smp_processor_id());
-
/*
* Clear them before re-enabling irqs/NMIs again:
*/
cpuc->interrupts = 0;
- hw_perf_restore(cpuc->throttle_ctrl);
+ perf_enable();
} else {
cpuc->interrupts = 0;
}
@@ -931,8 +900,8 @@ static __read_mostly struct notifier_block perf_counter_nmi_notifier = {
static struct x86_pmu intel_pmu = {
.name = "Intel",
.handle_irq = intel_pmu_handle_irq,
- .save_disable_all = intel_pmu_save_disable_all,
- .restore_all = intel_pmu_restore_all,
+ .disable_all = intel_pmu_disable_all,
+ .enable_all = intel_pmu_enable_all,
.enable = intel_pmu_enable_counter,
.disable = intel_pmu_disable_counter,
.eventsel = MSR_ARCH_PERFMON_EVENTSEL0,
@@ -951,8 +920,8 @@ static struct x86_pmu intel_pmu = {
static struct x86_pmu amd_pmu = {
.name = "AMD",
.handle_irq = amd_pmu_handle_irq,
- .save_disable_all = amd_pmu_save_disable_all,
- .restore_all = amd_pmu_restore_all,
+ .disable_all = amd_pmu_disable_all,
+ .enable_all = amd_pmu_enable_all,
.enable = amd_pmu_enable_counter,
.disable = amd_pmu_disable_counter,
.eventsel = MSR_K7_EVNTSEL0,
@@ -1003,6 +972,8 @@ static int intel_pmu_init(void)
x86_pmu.counter_bits = eax.split.bit_width;
x86_pmu.counter_mask = (1ULL << eax.split.bit_width) - 1;

+ rdmsrl(MSR_CORE_PERF_GLOBAL_CTRL, x86_pmu.intel_ctrl);
+
return 0;
}

diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
index d2830f3..9645758 100644
--- a/drivers/acpi/processor_idle.c
+++ b/drivers/acpi/processor_idle.c
@@ -763,11 +763,9 @@ static int acpi_idle_bm_check(void)
*/
static inline void acpi_idle_do_entry(struct acpi_processor_cx *cx)
{
- u64 perf_flags;
-
/* Don't trace irqs off for idle */
stop_critical_timings();
- perf_flags = hw_perf_save_disable();
+ perf_disable();
if (cx->entry_method == ACPI_CSTATE_FFH) {
/* Call into architectural FFH based C-state */
acpi_processor_ffh_cstate_enter(cx);
@@ -782,7 +780,7 @@ static inline void acpi_idle_do_entry(struct acpi_processor_cx *cx)
gets asserted in time to freeze execution properly. */
unused = inl(acpi_gbl_FADT.xpm_timer_block.address);
}
- hw_perf_restore(perf_flags);
+ perf_enable();
start_critical_timings();
}

diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h
index 614f921..e543ecc 100644
--- a/include/linux/perf_counter.h
+++ b/include/linux/perf_counter.h
@@ -544,8 +544,10 @@ extern void perf_counter_exit_task(struct task_struct *child);
extern void perf_counter_do_pending(void);
extern void perf_counter_print_debug(void);
extern void perf_counter_unthrottle(void);
-extern u64 hw_perf_save_disable(void);
-extern void hw_perf_restore(u64 ctrl);
+extern void __perf_disable(void);
+extern bool __perf_enable(void);
+extern void perf_disable(void);
+extern void perf_enable(void);
extern int perf_counter_task_disable(void);
extern int perf_counter_task_enable(void);
extern int hw_perf_group_sched_in(struct perf_counter *group_leader,
@@ -600,8 +602,8 @@ static inline void perf_counter_exit_task(struct task_struct *child) { }
static inline void perf_counter_do_pending(void) { }
static inline void perf_counter_print_debug(void) { }
static inline void perf_counter_unthrottle(void) { }
-static inline void hw_perf_restore(u64 ctrl) { }
-static inline u64 hw_perf_save_disable(void) { return 0; }
+static inline void perf_disable(void) { }
+static inline void perf_enable(void) { }
static inline int perf_counter_task_disable(void) { return -EINVAL; }
static inline int perf_counter_task_enable(void) { return -EINVAL; }

diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index 985be0b..e814ff0 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -60,8 +60,9 @@ extern __weak const struct pmu *hw_perf_counter_init(struct perf_counter *counte
return NULL;
}

-u64 __weak hw_perf_save_disable(void) { return 0; }
-void __weak hw_perf_restore(u64 ctrl) { barrier(); }
+void __weak hw_perf_disable(void) { barrier(); }
+void __weak hw_perf_enable(void) { barrier(); }
+
void __weak hw_perf_counter_setup(int cpu) { barrier(); }
int __weak hw_perf_group_sched_in(struct perf_counter *group_leader,
struct perf_cpu_context *cpuctx,
@@ -72,6 +73,32 @@ int __weak hw_perf_group_sched_in(struct perf_counter *group_leader,

void __weak perf_counter_print_debug(void) { }

+static DEFINE_PER_CPU(int, disable_count);
+
+void __perf_disable(void)
+{
+ __get_cpu_var(disable_count)++;
+}
+
+bool __perf_enable(void)
+{
+ return !--__get_cpu_var(disable_count);
+}
+
+void perf_disable(void)
+{
+ __perf_disable();
+ hw_perf_disable();
+}
+EXPORT_SYMBOL_GPL(perf_disable); /* ACPI idle */
+
+void perf_enable(void)
+{
+ if (__perf_enable())
+ hw_perf_enable();
+}
+EXPORT_SYMBOL_GPL(perf_enable); /* ACPI idle */
+
static void
list_add_counter(struct perf_counter *counter, struct perf_counter_context *ctx)
{
@@ -170,7 +197,6 @@ static void __perf_counter_remove_from_context(void *info)
struct perf_counter *counter = info;
struct perf_counter_context *ctx = counter->ctx;
unsigned long flags;
- u64 perf_flags;

/*
* If this is a task context, we need to check whether it is
@@ -191,9 +217,9 @@ static void __perf_counter_remove_from_context(void *info)
* Protect the list operation against NMI by disabling the
* counters on a global level. NOP for non NMI based counters.
*/
- perf_flags = hw_perf_save_disable();
+ perf_disable();
list_del_counter(counter, ctx);
- hw_perf_restore(perf_flags);
+ perf_enable();

if (!ctx->task) {
/*
@@ -538,7 +564,6 @@ static void __perf_install_in_context(void *info)
struct perf_counter *leader = counter->group_leader;
int cpu = smp_processor_id();
unsigned long flags;
- u64 perf_flags;
int err;

/*
@@ -556,7 +581,7 @@ static void __perf_install_in_context(void *info)
* Protect the list operation against NMI by disabling the
* counters on a global level. NOP for non NMI based counters.
*/
- perf_flags = hw_perf_save_disable();
+ perf_disable();

add_counter_to_ctx(counter, ctx);

@@ -596,7 +621,7 @@ static void __perf_install_in_context(void *info)
cpuctx->max_pertask--;

unlock:
- hw_perf_restore(perf_flags);
+ perf_enable();

spin_unlock_irqrestore(&ctx->lock, flags);
}
@@ -663,7 +688,6 @@ static void __perf_counter_enable(void *info)
struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
struct perf_counter_context *ctx = counter->ctx;
struct perf_counter *leader = counter->group_leader;
- unsigned long pmuflags;
unsigned long flags;
int err;

@@ -693,14 +717,14 @@ static void __perf_counter_enable(void *info)
if (!group_can_go_on(counter, cpuctx, 1)) {
err = -EEXIST;
} else {
- pmuflags = hw_perf_save_disable();
+ perf_disable();
if (counter == leader)
err = group_sched_in(counter, cpuctx, ctx,
smp_processor_id());
else
err = counter_sched_in(counter, cpuctx, ctx,
smp_processor_id());
- hw_perf_restore(pmuflags);
+ perf_enable();
}

if (err) {
@@ -795,7 +819,6 @@ void __perf_counter_sched_out(struct perf_counter_context *ctx,
struct perf_cpu_context *cpuctx)
{
struct perf_counter *counter;
- u64 flags;

spin_lock(&ctx->lock);
ctx->is_active = 0;
@@ -803,12 +826,12 @@ void __perf_counter_sched_out(struct perf_counter_context *ctx,
goto out;
update_context_time(ctx);

- flags = hw_perf_save_disable();
+ perf_disable();
if (ctx->nr_active) {
list_for_each_entry(counter, &ctx->counter_list, list_entry)
group_sched_out(counter, cpuctx, ctx);
}
- hw_perf_restore(flags);
+ perf_enable();
out:
spin_unlock(&ctx->lock);
}
@@ -860,7 +883,6 @@ __perf_counter_sched_in(struct perf_counter_context *ctx,
struct perf_cpu_context *cpuctx, int cpu)
{
struct perf_counter *counter;
- u64 flags;
int can_add_hw = 1;

spin_lock(&ctx->lock);
@@ -870,7 +892,7 @@ __perf_counter_sched_in(struct perf_counter_context *ctx,

ctx->timestamp = perf_clock();

- flags = hw_perf_save_disable();
+ perf_disable();

/*
* First go through the list and put on any pinned groups
@@ -917,7 +939,7 @@ __perf_counter_sched_in(struct perf_counter_context *ctx,
can_add_hw = 0;
}
}
- hw_perf_restore(flags);
+ perf_enable();
out:
spin_unlock(&ctx->lock);
}
@@ -955,7 +977,6 @@ int perf_counter_task_disable(void)
struct perf_counter_context *ctx = &curr->perf_counter_ctx;
struct perf_counter *counter;
unsigned long flags;
- u64 perf_flags;

if (likely(!ctx->nr_counters))
return 0;
@@ -969,7 +990,7 @@ int perf_counter_task_disable(void)
/*
* Disable all the counters:
*/
- perf_flags = hw_perf_save_disable();
+ perf_disable();

list_for_each_entry(counter, &ctx->counter_list, list_entry) {
if (counter->state != PERF_COUNTER_STATE_ERROR) {
@@ -978,7 +999,7 @@ int perf_counter_task_disable(void)
}
}

- hw_perf_restore(perf_flags);
+ perf_enable();

spin_unlock_irqrestore(&ctx->lock, flags);

@@ -991,7 +1012,6 @@ int perf_counter_task_enable(void)
struct perf_counter_context *ctx = &curr->perf_counter_ctx;
struct perf_counter *counter;
unsigned long flags;
- u64 perf_flags;
int cpu;

if (likely(!ctx->nr_counters))
@@ -1007,7 +1027,7 @@ int perf_counter_task_enable(void)
/*
* Disable all the counters:
*/
- perf_flags = hw_perf_save_disable();
+ perf_disable();

list_for_each_entry(counter, &ctx->counter_list, list_entry) {
if (counter->state > PERF_COUNTER_STATE_OFF)
@@ -1017,7 +1037,7 @@ int perf_counter_task_enable(void)
ctx->time - counter->total_time_enabled;
counter->hw_event.disabled = 0;
}
- hw_perf_restore(perf_flags);
+ perf_enable();

spin_unlock(&ctx->lock);

@@ -1034,7 +1054,6 @@ int perf_counter_task_enable(void)
static void rotate_ctx(struct perf_counter_context *ctx)
{
struct perf_counter *counter;
- u64 perf_flags;

if (!ctx->nr_counters)
return;
@@ -1043,12 +1062,12 @@ static void rotate_ctx(struct perf_counter_context *ctx)
/*
* Rotate the first entry last (works just fine for group counters too):
*/
- perf_flags = hw_perf_save_disable();
+ perf_disable();
list_for_each_entry(counter, &ctx->counter_list, list_entry) {
list_move_tail(&counter->list_entry, &ctx->counter_list);
break;
}
- hw_perf_restore(perf_flags);
+ perf_enable();

spin_unlock(&ctx->lock);
}
@@ -3194,7 +3213,6 @@ __perf_counter_exit_task(struct task_struct *child,
} else {
struct perf_cpu_context *cpuctx;
unsigned long flags;
- u64 perf_flags;

/*
* Disable and unlink this counter.
@@ -3203,7 +3221,7 @@ __perf_counter_exit_task(struct task_struct *child,
* could still be processing it:
*/
local_irq_save(flags);
- perf_flags = hw_perf_save_disable();
+ perf_disable();

cpuctx = &__get_cpu_var(perf_cpu_context);

@@ -3214,7 +3232,7 @@ __perf_counter_exit_task(struct task_struct *child,

child_ctx->nr_counters--;

- hw_perf_restore(perf_flags);
+ perf_enable();
local_irq_restore(flags);
}

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