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perf/x86/intel: Rework the large PEBS setup code

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In order to allow optimizing perf_pmu_sched_task() we must ensure
perf_sched_cb_{inc,dec}() are no longer called from NMI context; this
means that pmu::{start,stop}() can no longer use them.

Prepare for this by reworking the whole large PEBS setup code.

The current code relied on the cpuc->pebs_enabled state, however since
that reflects the current active state as per pmu::{start,stop}() we
can no longer rely on this.

Introduce two counters: cpuc->n_pebs and cpuc->n_large_pebs which
count the total number of PEBS events and the number of PEBS events
that have FREERUNNING set, resp.. With this we can tell if the current
setup requires a single record interrupt threshold or can use a larger
buffer.

This also improves the code in that it re-enables the large threshold
once the PEBS event that required single record gets removed.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra 2016-07-06 18:02:43 +02:00 committed by Ingo Molnar
parent 3f005e7de3
commit 09e61b4f78
3 changed files with 73 additions and 35 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

102
arch/x86/events/intel/ds.c
View file

@ -806,9 +806,55 @@ struct event_constraint *intel_pebs_constraints(struct perf_event *event)
return &emptyconstraint;
}
static inline bool pebs_is_enabled(struct cpu_hw_events *cpuc)
/*
* We need the sched_task callback even for per-cpu events when we use
* the large interrupt threshold, such that we can provide PID and TID
* to PEBS samples.
*/
static inline bool pebs_needs_sched_cb(struct cpu_hw_events *cpuc)
{
return (cpuc->pebs_enabled & ((1ULL << MAX_PEBS_EVENTS) - 1));
return cpuc->n_pebs && (cpuc->n_pebs == cpuc->n_large_pebs);
}
static inline void pebs_update_threshold(struct cpu_hw_events *cpuc)
{
struct debug_store *ds = cpuc->ds;
u64 threshold;
if (cpuc->n_pebs == cpuc->n_large_pebs) {
threshold = ds->pebs_absolute_maximum -
x86_pmu.max_pebs_events * x86_pmu.pebs_record_size;
} else {
threshold = ds->pebs_buffer_base + x86_pmu.pebs_record_size;
}
ds->pebs_interrupt_threshold = threshold;
}
static void
pebs_update_state(bool needed_cb, struct cpu_hw_events *cpuc, struct pmu *pmu)
{
if (needed_cb != pebs_needs_sched_cb(cpuc)) {
if (!needed_cb)
perf_sched_cb_inc(pmu);
else
perf_sched_cb_dec(pmu);
pebs_update_threshold(cpuc);
}
}
static void intel_pmu_pebs_add(struct perf_event *event)
{
struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
struct hw_perf_event *hwc = &event->hw;
bool needed_cb = pebs_needs_sched_cb(cpuc);
cpuc->n_pebs++;
if (hwc->flags & PERF_X86_EVENT_FREERUNNING)
cpuc->n_large_pebs++;
pebs_update_state(needed_cb, cpuc, event->ctx->pmu);
}
void intel_pmu_pebs_enable(struct perf_event *event)
@ -816,12 +862,11 @@ void intel_pmu_pebs_enable(struct perf_event *event)
struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
struct hw_perf_event *hwc = &event->hw;
struct debug_store *ds = cpuc->ds;
bool first_pebs;
u64 threshold;
intel_pmu_pebs_add(event);
hwc->config &= ~ARCH_PERFMON_EVENTSEL_INT;
first_pebs = !pebs_is_enabled(cpuc);
cpuc->pebs_enabled |= 1ULL << hwc->idx;
if (event->hw.flags & PERF_X86_EVENT_PEBS_LDLAT)
@ -830,46 +875,34 @@ void intel_pmu_pebs_enable(struct perf_event *event)
cpuc->pebs_enabled |= 1ULL << 63;
/*
* When the event is constrained enough we can use a larger
* threshold and run the event with less frequent PMI.
* Use auto-reload if possible to save a MSR write in the PMI.
* This must be done in pmu::start(), because PERF_EVENT_IOC_PERIOD.
*/
if (hwc->flags & PERF_X86_EVENT_FREERUNNING) {
threshold = ds->pebs_absolute_maximum -
x86_pmu.max_pebs_events * x86_pmu.pebs_record_size;
if (first_pebs)
perf_sched_cb_inc(event->ctx->pmu);
} else {
threshold = ds->pebs_buffer_base + x86_pmu.pebs_record_size;
/*
* If not all events can use larger buffer,
* roll back to threshold = 1
*/
if (!first_pebs &&
(ds->pebs_interrupt_threshold > threshold))
perf_sched_cb_dec(event->ctx->pmu);
}
/* Use auto-reload if possible to save a MSR write in the PMI */
if (hwc->flags & PERF_X86_EVENT_AUTO_RELOAD) {
ds->pebs_event_reset[hwc->idx] =
(u64)(-hwc->sample_period) & x86_pmu.cntval_mask;
}
}
if (first_pebs || ds->pebs_interrupt_threshold > threshold)
ds->pebs_interrupt_threshold = threshold;
static void intel_pmu_pebs_del(struct perf_event *event)
{
struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
struct hw_perf_event *hwc = &event->hw;
bool needed_cb = pebs_needs_sched_cb(cpuc);
cpuc->n_pebs--;
if (hwc->flags & PERF_X86_EVENT_FREERUNNING)
cpuc->n_large_pebs--;
pebs_update_state(needed_cb, cpuc, event->ctx->pmu);
}
void intel_pmu_pebs_disable(struct perf_event *event)
{
struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
struct hw_perf_event *hwc = &event->hw;
struct debug_store *ds = cpuc->ds;
bool large_pebs = ds->pebs_interrupt_threshold >
ds->pebs_buffer_base + x86_pmu.pebs_record_size;
if (large_pebs)
if (cpuc->n_pebs == cpuc->n_large_pebs)
intel_pmu_drain_pebs_buffer();
cpuc->pebs_enabled &= ~(1ULL << hwc->idx);
@ -879,13 +912,12 @@ void intel_pmu_pebs_disable(struct perf_event *event)
else if (event->hw.flags & PERF_X86_EVENT_PEBS_ST)
cpuc->pebs_enabled &= ~(1ULL << 63);
if (large_pebs && !pebs_is_enabled(cpuc))
perf_sched_cb_dec(event->ctx->pmu);
if (cpuc->enabled)
wrmsrl(MSR_IA32_PEBS_ENABLE, cpuc->pebs_enabled);
hwc->config |= ARCH_PERFMON_EVENTSEL_INT;
intel_pmu_pebs_del(event);
}
void intel_pmu_pebs_enable_all(void)

2
arch/x86/events/perf_event.h
View file

@ -194,6 +194,8 @@ struct cpu_hw_events {
*/
struct debug_store *ds;
u64 pebs_enabled;
int n_pebs;
int n_large_pebs;
/*
* Intel LBR bits

4
kernel/events/core.c
View file

@ -2818,6 +2818,10 @@ void perf_sched_cb_inc(struct pmu *pmu)
/*
* This function provides the context switch callback to the lower code
* layer. It is invoked ONLY when the context switch callback is enabled.
*
* This callback is relevant even to per-cpu events; for example multi event
* PEBS requires this to provide PID/TID information. This requires we flush
* all queued PEBS records before we context switch to a new task.
*/
static void perf_pmu_sched_task(struct task_struct *prev,
struct task_struct *next,