[PATCH v9 14/22] perf: Add perf_pmu_resched_update()

[Colton Lewis]

To modify PMU guest counter reservations dynamically, the per-CPU
available counter mask must be updated while host perf events are
temporarily scheduled out.

Introduce perf_pmu_resched_update() to update PMU state while holding
cpuctx->ctx.lock in between scheduling perf events out and scheduling
them back in. It accepts a callback invoked between ctx_sched_out() and
perf_event_sched_in(), accomplishing atomic counter mask updates with
minimal perf API expansion.

Refactor ctx_resched() into __ctx_resched() to invoke the callback at
the appropriate point.

Signed-off-by: Colton Lewis <coltonlewis@xxxxxxxxxx>
---
 include/linux/perf_event.h |  3 +++
 kernel/events/core.c       | 31 ++++++++++++++++++++++++++++---
 2 files changed, 31 insertions(+), 3 deletions(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 5842552294c19..32e3c0d365963 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1242,6 +1242,9 @@ extern int perf_event_task_disable(void);
 extern int perf_event_task_enable(void);
 
 extern void perf_pmu_resched(struct pmu *pmu);
+extern void perf_pmu_resched_update(struct pmu *pmu,
+				    void (*update)(struct pmu *, void *),
+				    void *data);
 
 extern int perf_event_refresh(struct perf_event *event, int refresh);
 extern void perf_event_update_userpage(struct perf_event *event);
diff --git a/kernel/events/core.c b/kernel/events/core.c
index db7b76d6b68aa..06d1128d194fa 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -2991,9 +2991,10 @@ static void perf_event_sched_in(struct perf_cpu_context *cpuctx,
  * event_type is a bit mask of the types of events involved. For CPU events,
  * event_type is only either EVENT_PINNED or EVENT_FLEXIBLE.
  */
-static void ctx_resched(struct perf_cpu_context *cpuctx,
-			struct perf_event_context *task_ctx,
-			struct pmu *pmu, enum event_type_t event_type)
+static void __ctx_resched(struct perf_cpu_context *cpuctx,
+			  struct perf_event_context *task_ctx,
+			  struct pmu *pmu, enum event_type_t event_type,
+			  void (*update)(struct pmu *, void *), void *data)
 {
 	bool cpu_event = !!(event_type & EVENT_CPU);
 	struct perf_event_pmu_context *epc;
@@ -3029,6 +3030,9 @@ static void ctx_resched(struct perf_cpu_context *cpuctx,
 	else if (event_type & EVENT_PINNED)
 		ctx_sched_out(&cpuctx->ctx, pmu, EVENT_FLEXIBLE);
 
+	if (update)
+		update(pmu, data);
+
 	perf_event_sched_in(cpuctx, task_ctx, pmu, 0);
 
 	for_each_epc(epc, &cpuctx->ctx, pmu, 0)
@@ -3040,6 +3044,27 @@ static void ctx_resched(struct perf_cpu_context *cpuctx,
 	}
 }
 
+static void ctx_resched(struct perf_cpu_context *cpuctx,
+			struct perf_event_context *task_ctx,
+			struct pmu *pmu, enum event_type_t event_type)
+{
+	__ctx_resched(cpuctx, task_ctx, pmu, event_type, NULL, NULL);
+}
+
+void perf_pmu_resched_update(struct pmu *pmu, void (*update)(struct pmu *, void *), void *data)
+{
+	struct perf_cpu_context *cpuctx = this_cpu_ptr(&perf_cpu_context);
+	struct perf_event_context *task_ctx = cpuctx->task_ctx;
+	unsigned long flags;
+
+	local_irq_save(flags);
+	perf_ctx_lock(cpuctx, task_ctx);
+	__ctx_resched(cpuctx, task_ctx, pmu, EVENT_ALL|EVENT_CPU, update, data);
+	perf_ctx_unlock(cpuctx, task_ctx);
+	local_irq_restore(flags);
+}
+EXPORT_SYMBOL_GPL(perf_pmu_resched_update);
+
 void perf_pmu_resched(struct pmu *pmu)
 {
 	struct perf_cpu_context *cpuctx = this_cpu_ptr(&perf_cpu_context);
-- 
2.56.0.rc1.310.g51773c2048-goog