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perfcounters: restructure x86 counter math
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Impact: restructure code

Change counter math from absolute values to clear delta logic.

We try to extract elapsed deltas from the raw hw counter - and put
that into the generic counter.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
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Ingo Molnar committed Dec 14, 2008
1 parent 9b194e8 commit ee06094
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Showing 4 changed files with 137 additions and 178 deletions.
2 changes: 1 addition & 1 deletion arch/x86/Kconfig
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Original file line number Diff line number Diff line change
Expand Up @@ -643,7 +643,7 @@ config X86_UP_IOAPIC
config X86_LOCAL_APIC
def_bool y
depends on X86_64 || (X86_32 && (X86_UP_APIC || (SMP && !X86_VOYAGER) || X86_GENERICARCH))
select HAVE_PERF_COUNTERS
select HAVE_PERF_COUNTERS if (!M386 && !M486)

config X86_IO_APIC
def_bool y
Expand Down
230 changes: 124 additions & 106 deletions arch/x86/kernel/cpu/perf_counter.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -53,6 +53,48 @@ const int intel_perfmon_event_map[] =

const int max_intel_perfmon_events = ARRAY_SIZE(intel_perfmon_event_map);

/*
* Propagate counter elapsed time into the generic counter.
* Can only be executed on the CPU where the counter is active.
* Returns the delta events processed.
*/
static void
x86_perf_counter_update(struct perf_counter *counter,
struct hw_perf_counter *hwc, int idx)
{
u64 prev_raw_count, new_raw_count, delta;

WARN_ON_ONCE(counter->state != PERF_COUNTER_STATE_ACTIVE);
/*
* Careful: an NMI might modify the previous counter value.
*
* Our tactic to handle this is to first atomically read and
* exchange a new raw count - then add that new-prev delta
* count to the generic counter atomically:
*/
again:
prev_raw_count = atomic64_read(&hwc->prev_count);
rdmsrl(hwc->counter_base + idx, new_raw_count);

if (atomic64_cmpxchg(&hwc->prev_count, prev_raw_count,
new_raw_count) != prev_raw_count)
goto again;

/*
* Now we have the new raw value and have updated the prev
* timestamp already. We can now calculate the elapsed delta
* (counter-)time and add that to the generic counter.
*
* Careful, not all hw sign-extends above the physical width
* of the count, so we do that by clipping the delta to 32 bits:
*/
delta = (u64)(u32)((s32)new_raw_count - (s32)prev_raw_count);
WARN_ON_ONCE((int)delta < 0);

atomic64_add(delta, &counter->count);
atomic64_sub(delta, &hwc->period_left);
}

/*
* Setup the hardware configuration for a given hw_event_type
*/
Expand Down Expand Up @@ -90,10 +132,10 @@ static int __hw_perf_counter_init(struct perf_counter *counter)
* so we install an artificial 1<<31 period regardless of
* the generic counter period:
*/
if (!hwc->irq_period)
if ((s64)hwc->irq_period <= 0 || hwc->irq_period > 0x7FFFFFFF)
hwc->irq_period = 0x7FFFFFFF;

hwc->next_count = -(s32)hwc->irq_period;
atomic64_set(&hwc->period_left, hwc->irq_period);

/*
* Raw event type provide the config in the event structure
Expand All @@ -118,12 +160,6 @@ void hw_perf_enable_all(void)
wrmsr(MSR_CORE_PERF_GLOBAL_CTRL, perf_counter_mask, 0);
}

void hw_perf_restore(u64 ctrl)
{
wrmsr(MSR_CORE_PERF_GLOBAL_CTRL, ctrl, 0);
}
EXPORT_SYMBOL_GPL(hw_perf_restore);

u64 hw_perf_save_disable(void)
{
u64 ctrl;
Expand All @@ -134,27 +170,74 @@ u64 hw_perf_save_disable(void)
}
EXPORT_SYMBOL_GPL(hw_perf_save_disable);

void hw_perf_restore(u64 ctrl)
{
wrmsr(MSR_CORE_PERF_GLOBAL_CTRL, ctrl, 0);
}
EXPORT_SYMBOL_GPL(hw_perf_restore);

static inline void
__x86_perf_counter_disable(struct hw_perf_counter *hwc, unsigned int idx)
__x86_perf_counter_disable(struct perf_counter *counter,
struct hw_perf_counter *hwc, unsigned int idx)
{
wrmsr(hwc->config_base + idx, hwc->config, 0);
int err;

err = wrmsr_safe(hwc->config_base + idx, hwc->config, 0);
WARN_ON_ONCE(err);
}

static DEFINE_PER_CPU(u64, prev_next_count[MAX_HW_COUNTERS]);
static DEFINE_PER_CPU(u64, prev_left[MAX_HW_COUNTERS]);

static void __hw_perf_counter_set_period(struct hw_perf_counter *hwc, int idx)
/*
* Set the next IRQ period, based on the hwc->period_left value.
* To be called with the counter disabled in hw:
*/
static void
__hw_perf_counter_set_period(struct perf_counter *counter,
struct hw_perf_counter *hwc, int idx)
{
per_cpu(prev_next_count[idx], smp_processor_id()) = hwc->next_count;
s32 left = atomic64_read(&hwc->period_left);
s32 period = hwc->irq_period;

WARN_ON_ONCE(period <= 0);

/*
* If we are way outside a reasoable range then just skip forward:
*/
if (unlikely(left <= -period)) {
left = period;
atomic64_set(&hwc->period_left, left);
}

if (unlikely(left <= 0)) {
left += period;
atomic64_set(&hwc->period_left, left);
}

wrmsr(hwc->counter_base + idx, hwc->next_count, 0);
WARN_ON_ONCE(left <= 0);

per_cpu(prev_left[idx], smp_processor_id()) = left;

/*
* The hw counter starts counting from this counter offset,
* mark it to be able to extra future deltas:
*/
atomic64_set(&hwc->prev_count, (u64)(s64)-left);

wrmsr(hwc->counter_base + idx, -left, 0);
}

static void __x86_perf_counter_enable(struct hw_perf_counter *hwc, int idx)
static void
__x86_perf_counter_enable(struct perf_counter *counter,
struct hw_perf_counter *hwc, int idx)
{
wrmsr(hwc->config_base + idx,
hwc->config | ARCH_PERFMON_EVENTSEL0_ENABLE, 0);
}

/*
* Find a PMC slot for the freshly enabled / scheduled in counter:
*/
static void x86_perf_counter_enable(struct perf_counter *counter)
{
struct cpu_hw_counters *cpuc = &__get_cpu_var(cpu_hw_counters);
Expand All @@ -170,55 +253,17 @@ static void x86_perf_counter_enable(struct perf_counter *counter)

perf_counters_lapic_init(hwc->nmi);

__x86_perf_counter_disable(hwc, idx);
__x86_perf_counter_disable(counter, hwc, idx);

cpuc->counters[idx] = counter;

__hw_perf_counter_set_period(hwc, idx);
__x86_perf_counter_enable(hwc, idx);
}

static void __hw_perf_save_counter(struct perf_counter *counter,
struct hw_perf_counter *hwc, int idx)
{
s64 raw = -1;
s64 delta;

/*
* Get the raw hw counter value:
*/
rdmsrl(hwc->counter_base + idx, raw);

/*
* Rebase it to zero (it started counting at -irq_period),
* to see the delta since ->prev_count:
*/
delta = (s64)hwc->irq_period + (s64)(s32)raw;

atomic64_counter_set(counter, hwc->prev_count + delta);

/*
* Adjust the ->prev_count offset - if we went beyond
* irq_period of units, then we got an IRQ and the counter
* was set back to -irq_period:
*/
while (delta >= (s64)hwc->irq_period) {
hwc->prev_count += hwc->irq_period;
delta -= (s64)hwc->irq_period;
}

/*
* Calculate the next raw counter value we'll write into
* the counter at the next sched-in time:
*/
delta -= (s64)hwc->irq_period;

hwc->next_count = (s32)delta;
__hw_perf_counter_set_period(counter, hwc, idx);
__x86_perf_counter_enable(counter, hwc, idx);
}

void perf_counter_print_debug(void)
{
u64 ctrl, status, overflow, pmc_ctrl, pmc_count, next_count;
u64 ctrl, status, overflow, pmc_ctrl, pmc_count, prev_left;
int cpu, idx;

if (!nr_hw_counters)
Expand All @@ -241,14 +286,14 @@ void perf_counter_print_debug(void)
rdmsrl(MSR_ARCH_PERFMON_EVENTSEL0 + idx, pmc_ctrl);
rdmsrl(MSR_ARCH_PERFMON_PERFCTR0 + idx, pmc_count);

next_count = per_cpu(prev_next_count[idx], cpu);
prev_left = per_cpu(prev_left[idx], cpu);

printk(KERN_INFO "CPU#%d: PMC%d ctrl: %016llx\n",
cpu, idx, pmc_ctrl);
printk(KERN_INFO "CPU#%d: PMC%d count: %016llx\n",
cpu, idx, pmc_count);
printk(KERN_INFO "CPU#%d: PMC%d next: %016llx\n",
cpu, idx, next_count);
printk(KERN_INFO "CPU#%d: PMC%d left: %016llx\n",
cpu, idx, prev_left);
}
local_irq_enable();
}
Expand All @@ -259,29 +304,16 @@ static void x86_perf_counter_disable(struct perf_counter *counter)
struct hw_perf_counter *hwc = &counter->hw;
unsigned int idx = hwc->idx;

__x86_perf_counter_disable(hwc, idx);
__x86_perf_counter_disable(counter, hwc, idx);

clear_bit(idx, cpuc->used);
cpuc->counters[idx] = NULL;
__hw_perf_save_counter(counter, hwc, idx);
}

static void x86_perf_counter_read(struct perf_counter *counter)
{
struct hw_perf_counter *hwc = &counter->hw;
unsigned long addr = hwc->counter_base + hwc->idx;
s64 offs, val = -1LL;
s32 val32;

/* Careful: NMI might modify the counter offset */
do {
offs = hwc->prev_count;
rdmsrl(addr, val);
} while (offs != hwc->prev_count);

val32 = (s32) val;
val = (s64)hwc->irq_period + (s64)val32;
atomic64_counter_set(counter, hwc->prev_count + val);
/*
* Drain the remaining delta count out of a counter
* that we are disabling:
*/
x86_perf_counter_update(counter, hwc, idx);
}

static void perf_store_irq_data(struct perf_counter *counter, u64 data)
Expand All @@ -299,7 +331,8 @@ static void perf_store_irq_data(struct perf_counter *counter, u64 data)
}

/*
* NMI-safe enable method:
* Save and restart an expired counter. Called by NMI contexts,
* so it has to be careful about preempting normal counter ops:
*/
static void perf_save_and_restart(struct perf_counter *counter)
{
Expand All @@ -309,45 +342,25 @@ static void perf_save_and_restart(struct perf_counter *counter)

rdmsrl(MSR_ARCH_PERFMON_EVENTSEL0 + idx, pmc_ctrl);

__hw_perf_save_counter(counter, hwc, idx);
__hw_perf_counter_set_period(hwc, idx);
x86_perf_counter_update(counter, hwc, idx);
__hw_perf_counter_set_period(counter, hwc, idx);

if (pmc_ctrl & ARCH_PERFMON_EVENTSEL0_ENABLE)
__x86_perf_counter_enable(hwc, idx);
__x86_perf_counter_enable(counter, hwc, idx);
}

static void
perf_handle_group(struct perf_counter *sibling, u64 *status, u64 *overflown)
{
struct perf_counter *counter, *group_leader = sibling->group_leader;
int bit;

/*
* Store the counter's own timestamp first:
*/
perf_store_irq_data(sibling, sibling->hw_event.type);
perf_store_irq_data(sibling, atomic64_counter_read(sibling));

/*
* Then store sibling timestamps (if any):
* Store sibling timestamps (if any):
*/
list_for_each_entry(counter, &group_leader->sibling_list, list_entry) {
if (counter->state != PERF_COUNTER_STATE_ACTIVE) {
/*
* When counter was not in the overflow mask, we have to
* read it from hardware. We read it as well, when it
* has not been read yet and clear the bit in the
* status mask.
*/
bit = counter->hw.idx;
if (!test_bit(bit, (unsigned long *) overflown) ||
test_bit(bit, (unsigned long *) status)) {
clear_bit(bit, (unsigned long *) status);
perf_save_and_restart(counter);
}
}
x86_perf_counter_update(counter, &counter->hw, counter->hw.idx);
perf_store_irq_data(sibling, counter->hw_event.type);
perf_store_irq_data(sibling, atomic64_counter_read(counter));
perf_store_irq_data(sibling, atomic64_read(&counter->count));
}
}

Expand Down Expand Up @@ -540,6 +553,11 @@ void __init init_hw_perf_counters(void)
perf_counters_initialized = true;
}

static void x86_perf_counter_read(struct perf_counter *counter)
{
x86_perf_counter_update(counter, &counter->hw, counter->hw.idx);
}

static const struct hw_perf_counter_ops x86_perf_counter_ops = {
.hw_perf_counter_enable = x86_perf_counter_enable,
.hw_perf_counter_disable = x86_perf_counter_disable,
Expand Down
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