[tip:perfcounters/core] perf_counter: x86: Emulate longer sample periods

tip-bot for Peter Zijlstra
2009-06-02T20:18:12Z

Commit-ID: e4abb5d4f7ddabc1fc7c392cf0a10d8e5868c9ca
Gitweb: http://git.kernel.org/tip/e4abb5d4f7ddabc1fc7c392cf0a10d8e5868c9ca
Author: Peter Zijlstra <a.p.zijlstra@chello.nl>
AuthorDate: Tue, 2 Jun 2009 16:08:20 +0200
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Tue, 2 Jun 2009 21:45:31 +0200

perf_counter: x86: Emulate longer sample periods

Do as Power already does, emulate sample periods up to 2^63-1 by
composing them of smaller values limited by hardware capabilities.
Only once we wrap the software period do we generate an overflow
event.

Just 10 lines of new code.

Reported-by: Stephane Eranian <eranian@googlemail.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: John Kacur <jkacur@redhat.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

---
arch/x86/kernel/cpu/perf_counter.c | 31 ++++++++++++++++++++++---------
1 files changed, 22 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_counter.c b/arch/x86/kernel/cpu/perf_counter.c
index 9e144fb..904571b 100644
--- a/arch/x86/kernel/cpu/perf_counter.c
+++ b/arch/x86/kernel/cpu/perf_counter.c
@@ -287,8 +287,7 @@ static int __hw_perf_counter_init(struct perf_counter *counter)
if (!hwc->sample_period)
hwc->sample_period = x86_pmu.max_period;

- atomic64_set(&hwc->period_left,
- min(x86_pmu.max_period, hwc->sample_period));
+ atomic64_set(&hwc->period_left, hwc->sample_period);

/*
* Raw event type provide the config in the event structure
@@ -451,13 +450,13 @@ static DEFINE_PER_CPU(u64, prev_left[X86_PMC_IDX_MAX]);
* Set the next IRQ period, based on the hwc->period_left value.
* To be called with the counter disabled in hw:
*/
-static void
+static int
x86_perf_counter_set_period(struct perf_counter *counter,
struct hw_perf_counter *hwc, int idx)
{
s64 left = atomic64_read(&hwc->period_left);
- s64 period = min(x86_pmu.max_period, hwc->sample_period);
- int err;
+ s64 period = hwc->sample_period;
+ int err, ret = 0;

/*
* If we are way outside a reasoable range then just skip forward:
@@ -465,11 +464,13 @@ x86_perf_counter_set_period(struct perf_counter *counter,
if (unlikely(left <= -period)) {
left = period;
atomic64_set(&hwc->period_left, left);
+ ret = 1;
}

if (unlikely(left <= 0)) {
left += period;
atomic64_set(&hwc->period_left, left);
+ ret = 1;
}
/*
* Quirk: certain CPUs dont like it if just 1 event is left:
@@ -477,6 +478,9 @@ x86_perf_counter_set_period(struct perf_counter *counter,
if (unlikely(left < 2))
left = 2;

+ if (left > x86_pmu.max_period)
+ left = x86_pmu.max_period;
+
per_cpu(prev_left[idx], smp_processor_id()) = left;

/*
@@ -487,6 +491,8 @@ x86_perf_counter_set_period(struct perf_counter *counter,

err = checking_wrmsrl(hwc->counter_base + idx,
(u64)(-left) & x86_pmu.counter_mask);
+
+ return ret;
}

static inline void
@@ -706,16 +712,19 @@ static void x86_pmu_disable(struct perf_counter *counter)
* Save and restart an expired counter. Called by NMI contexts,
* so it has to be careful about preempting normal counter ops:
*/
-static void intel_pmu_save_and_restart(struct perf_counter *counter)
+static int intel_pmu_save_and_restart(struct perf_counter *counter)
{
struct hw_perf_counter *hwc = &counter->hw;
int idx = hwc->idx;
+ int ret;

x86_perf_counter_update(counter, hwc, idx);
- x86_perf_counter_set_period(counter, hwc, idx);
+ ret = x86_perf_counter_set_period(counter, hwc, idx);

if (counter->state == PERF_COUNTER_STATE_ACTIVE)
intel_pmu_enable_counter(hwc, idx);
+
+ return ret;
}

static void intel_pmu_reset(void)
@@ -782,7 +791,9 @@ again:
if (!test_bit(bit, cpuc->active_mask))
continue;

- intel_pmu_save_and_restart(counter);
+ if (!intel_pmu_save_and_restart(counter))
+ continue;
+
if (perf_counter_overflow(counter, nmi, regs, 0))
intel_pmu_disable_counter(&counter->hw, bit);
}
@@ -824,9 +835,11 @@ static int amd_pmu_handle_irq(struct pt_regs *regs, int nmi)
continue;

/* counter overflow */
- x86_perf_counter_set_period(counter, hwc, idx);
handled = 1;
inc_irq_stat(apic_perf_irqs);
+ if (!x86_perf_counter_set_period(counter, hwc, idx))
+ continue;
+
if (perf_counter_overflow(counter, nmi, regs, 0))
amd_pmu_disable_counter(hwc, idx);
}