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

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>

3 files changed, 73 insertions, 35 deletions

diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c
index 7ce9f3f669e6..c791ff961079 100644
--- a/arch/x86/events/intel/ds.c
+++ b/arch/x86/events/intel/ds.c
@@ -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->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)
 {
-        return (cpuc->pebs_enabled & ((1ULL << MAX_PEBS_EVENTS) - 1));
+        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;
         }
+}
+
+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--;
 
-        if (first_pebs || ds->pebs_interrupt_threshold > threshold)
-                ds->pebs_interrupt_threshold = threshold;
+        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)
diff --git a/arch/x86/events/perf_event.h b/arch/x86/events/perf_event.h
index 8c4a47706296..94b8f2702c51 100644
--- a/arch/x86/events/perf_event.h
+++ b/arch/x86/events/perf_event.h
@@ -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
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 11f6bbe168ab..57aff715039f 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -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,