perf: Add group scheduling transactional APIs

Add group scheduling transactional APIs to struct pmu.
These APIs will be implemented in arch code, based on Peter's idea as
below.

> the idea behind hw_perf_group_sched_in() is to not perform
> schedulability tests on each event in the group, but to add the group
> as a whole and then perform one test.
>
> Of course, when that test fails, you'll have to roll-back the whole
> group again.
>
> So start_txn (or a better name) would simply toggle a flag in the pmu
> implementation that will make pmu::enable() not perform the
> schedulablilty test.
>
> Then commit_txn() will perform the schedulability test (so note the
> method has to have a !void return value.
>
> This will allow us to use the regular
> kernel/perf_event.c::group_sched_in() and all the rollback code.
> Currently each hw_perf_group_sched_in() implementation duplicates all
> the rolllback code (with various bugs).

->start_txn:
Start group events scheduling transaction, set a flag to make
pmu::enable() not perform the schedulability test, it will be performed
at commit time.

->commit_txn:
Commit group events scheduling transaction, perform the group
schedulability as a whole

->cancel_txn:
Stop group events scheduling transaction, clear the flag so
pmu::enable() will perform the schedulability test.

Reviewed-by: Stephane Eranian <eranian@google.com>
Reviewed-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Lin Ming <ming.m.lin@intel.com>
Cc: David Miller <davem@davemloft.net>
Cc: Paul Mackerras <paulus@samba.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1272002160.5707.60.camel@minggr.sh.intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 32 insertions, 16 deletions

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 23cd0057a681..4924c96d7e2d 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -547,6 +547,8 @@ struct hw_perf_event {
 
 struct perf_event;
 
+#define PERF_EVENT_TXN_STARTED 1
+
 /**
  * struct pmu - generic performance monitoring unit
  */
@@ -557,6 +559,16 @@ struct pmu {
         void (*stop)                    (struct perf_event *event);
         void (*read)                    (struct perf_event *event);
         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
+         */
+
+        void (*start_txn)       (const struct pmu *pmu);
+        void (*cancel_txn)      (const struct pmu *pmu);
+        int  (*commit_txn)      (const struct pmu *pmu);
 };
 
 /**
@@ -823,9 +835,6 @@ extern void perf_disable(void);
 extern void perf_enable(void);
 extern int perf_event_task_disable(void);
 extern int perf_event_task_enable(void);
-extern int hw_perf_group_sched_in(struct perf_event *group_leader,
-               struct perf_cpu_context *cpuctx,
-               struct perf_event_context *ctx);
 extern void perf_event_update_userpage(struct perf_event *event);
 extern int perf_event_release_kernel(struct perf_event *event);
 extern struct perf_event *
diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 34659d4085c7..bb06382f98e7 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -83,14 +83,6 @@ extern __weak const struct pmu *hw_perf_event_init(struct perf_event *event)
 void __weak hw_perf_disable(void)               { barrier(); }
 void __weak hw_perf_enable(void)                { barrier(); }
 
-int __weak
-hw_perf_group_sched_in(struct perf_event *group_leader,
-               struct perf_cpu_context *cpuctx,
-               struct perf_event_context *ctx)
-{
-        return 0;
-}
-
 void __weak perf_event_print_debug(void)        { }
 
 static DEFINE_PER_CPU(int, perf_disable_count);
@@ -644,15 +636,20 @@ group_sched_in(struct perf_event *group_event,
                struct perf_cpu_context *cpuctx,
                struct perf_event_context *ctx)
 {
-        struct perf_event *event, *partial_group;
+        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;
 
-        ret = hw_perf_group_sched_in(group_event, cpuctx, ctx);
-        if (ret)
-                return ret < 0 ? ret : 0;
+        /* Check if group transaction availabe */
+        if (pmu->start_txn)
+                txn = true;
+
+        if (txn)
+                pmu->start_txn(pmu);
 
         if (event_sched_in(group_event, cpuctx, ctx))
                 return -EAGAIN;
@@ -667,9 +664,19 @@ group_sched_in(struct perf_event *group_event,
                 }
         }
 
-        return 0;
+        if (txn) {
+                ret = pmu->commit_txn(pmu);
+                if (!ret) {
+                        pmu->cancel_txn(pmu);
+
+                        return 0;
+                }
+        }
 
 group_error:
+        if (txn)
+                pmu->cancel_txn(pmu);
+
         /*
          * Groups can be scheduled in as one unit only, so undo any
          * partial group before returning: