perf: Cleanup {start,commit,cancel}_txn details

Clarify some of the transactional group scheduling API details
and change it so that a successfull ->commit_txn also closes
the transaction.

Signed-off-by: Peter Zijlstra <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Arnaldo Carvalho de Melo <[e-mail]>
Cc: Frederic Weisbecker <[e-mail]>
Cc: Paul Mackerras <[e-mail]>
Cc: Mike Galbraith <[e-mail]>
Cc: Steven Rostedt <[e-mail]>
LKML-Reference: <1274803086.5882.1752.camel@twins>
Signed-off-by: Ingo Molnar <[e-mail]>

arch/powerpc/kernel/perf_event.c

···
 	 * skip the schedulability test here, it will be peformed
 	 * at commit time(->commit_txn) as a whole
 	 */
-	if (cpuhw->group_flag & PERF_EVENT_TXN_STARTED)
+	if (cpuhw->group_flag & PERF_EVENT_TXN)
 		goto nocheck;
 
 	if (check_excludes(cpuhw->event, cpuhw->flags, n0, 1))
···
 {
 	struct cpu_hw_events *cpuhw = &__get_cpu_var(cpu_hw_events);
 
-	cpuhw->group_flag |= PERF_EVENT_TXN_STARTED;
+	cpuhw->group_flag |= PERF_EVENT_TXN;
 	cpuhw->n_txn_start = cpuhw->n_events;
 }
 
···
 {
 	struct cpu_hw_events *cpuhw = &__get_cpu_var(cpu_hw_events);
 
-	cpuhw->group_flag &= ~PERF_EVENT_TXN_STARTED;
+	cpuhw->group_flag &= ~PERF_EVENT_TXN;
 }
 
 /*
···
 	for (i = cpuhw->n_txn_start; i < n; ++i)
 		cpuhw->event[i]->hw.config = cpuhw->events[i];
 
+	cpuhw->group_flag &= ~PERF_EVENT_TXN;
 	return 0;
 }
 

arch/sparc/kernel/perf_event.c

···
 	 * skip the schedulability test here, it will be peformed
 	 * at commit time(->commit_txn) as a whole
 	 */
-	if (cpuc->group_flag & PERF_EVENT_TXN_STARTED)
+	if (cpuc->group_flag & PERF_EVENT_TXN)
 		goto nocheck;
 
 	if (check_excludes(cpuc->event, n0, 1))
···
 {
 	struct cpu_hw_events *cpuhw = &__get_cpu_var(cpu_hw_events);
 
-	cpuhw->group_flag |= PERF_EVENT_TXN_STARTED;
+	cpuhw->group_flag |= PERF_EVENT_TXN;
 }
 
 /*
···
 {
 	struct cpu_hw_events *cpuhw = &__get_cpu_var(cpu_hw_events);
 
-	cpuhw->group_flag &= ~PERF_EVENT_TXN_STARTED;
+	cpuhw->group_flag &= ~PERF_EVENT_TXN;
 }
 
 /*
···
 	if (sparc_check_constraints(cpuc->event, cpuc->events, n))
 		return -EAGAIN;
 
+	cpuc->group_flag &= ~PERF_EVENT_TXN;
 	return 0;
 }
 

arch/x86/kernel/cpu/perf_event.c

···
 	 * skip the schedulability test here, it will be peformed
 	 * at commit time(->commit_txn) as a whole
 	 */
-	if (cpuc->group_flag & PERF_EVENT_TXN_STARTED)
+	if (cpuc->group_flag & PERF_EVENT_TXN)
 		goto out;
 
 	ret = x86_pmu.schedule_events(cpuc, n, assign);
···
 	 * The events never got scheduled and ->cancel_txn will truncate
 	 * the event_list.
 	 */
-	if (cpuc->group_flag & PERF_EVENT_TXN_STARTED)
+	if (cpuc->group_flag & PERF_EVENT_TXN)
 		return;
 
 	x86_pmu_stop(event);
···
 {
 	struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);
 
-	cpuc->group_flag |= PERF_EVENT_TXN_STARTED;
+	cpuc->group_flag |= PERF_EVENT_TXN;
 	cpuc->n_txn = 0;
 }
 
···
 {
 	struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);
 
-	cpuc->group_flag &= ~PERF_EVENT_TXN_STARTED;
+	cpuc->group_flag &= ~PERF_EVENT_TXN;
 	/*
 	 * Truncate the collected events.
 	 */
···
 	 */
 	memcpy(cpuc->assign, assign, n*sizeof(int));
 
-	/*
-	 * Clear out the txn count so that ->cancel_txn() which gets
-	 * run after ->commit_txn() doesn't undo things.
-	 */
-	cpuc->n_txn = 0;
+	cpuc->group_flag &= ~PERF_EVENT_TXN;
 
 	return 0;
 }

include/linux/perf_event.h

···
 
 struct perf_event;
 
-#define PERF_EVENT_TXN_STARTED 1
+/*
+ * Common implementation detail of pmu::{start,commit,cancel}_txn
+ */
+#define PERF_EVENT_TXN 0x1
 
 /**
  * struct pmu - generic performance monitoring unit
···
 	void (*unthrottle)		(struct perf_event *event);
 
 	/*
-	 * group events scheduling is treated as a transaction,
-	 * add group events as a whole and perform one schedulability test.
-	 * If test fails, roll back the whole group
+	 * Group events scheduling is treated as a transaction, add group
+	 * events as a whole and perform one schedulability test. If the test
+	 * fails, roll back the whole group
 	 */
 
+	/*
+	 * Start the transaction, after this ->enable() doesn't need
+	 * to do schedulability tests.
+	 */
 	void (*start_txn)	(const struct pmu *pmu);
-	void (*cancel_txn)	(const struct pmu *pmu);
+	/*
+	 * If ->start_txn() disabled the ->enable() schedulability test
+	 * then ->commit_txn() is required to perform one. On success
+	 * the transaction is closed. On error the transaction is kept
+	 * open until ->cancel_txn() is called.
+	 */
 	int  (*commit_txn)	(const struct pmu *pmu);
+	/*
+	 * Will cancel the transaction, assumes ->disable() is called for
+	 * each successfull ->enable() during the transaction.
+	 */
+	void (*cancel_txn)	(const struct pmu *pmu);
 };
 
 /**

kernel/perf_event.c

···
 	struct perf_event *event, *partial_group = NULL;
 	const struct pmu *pmu = group_event->pmu;
 	bool txn = false;
-	int ret;
 
 	if (group_event->state == PERF_EVENT_STATE_OFF)
 		return 0;
···
 		}
 	}
 
-	if (!txn)
+	if (!txn || !pmu->commit_txn(pmu))
 		return 0;
-
-	ret = pmu->commit_txn(pmu);
-	if (!ret) {
-		pmu->cancel_txn(pmu);
-		return 0;
-	}
 
 group_error:
 	/*