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 <a.p.zijlstra@chello.nl>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <1274803086.5882.1752.camel@twins>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 22 insertions, 5 deletions

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 36efad90cd43..f1b6ba0770e0 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -549,7 +549,10 @@ struct hw_perf_event {
 
 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
@@ -563,14 +566,28 @@ struct pmu {
         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);
 };
 
 /**