perf: Default PMU ops

Provide default implementations for the pmu txn methods, this
allows us to remove some conditional code.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: paulus <paulus@samba.org>
Cc: stephane eranian <eranian@googlemail.com>
Cc: Robert Richter <robert.richter@amd.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Lin Ming <ming.m.lin@intel.com>
Cc: Yanmin <yanmin_zhang@linux.intel.com>
Cc: Deng-Cheng Zhu <dengcheng.zhu@gmail.com>
Cc: David Miller <davem@davemloft.net>
Cc: Michael Cree <mcree@orcon.net.nz>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 57 insertions, 17 deletions

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 6abf103fb7f8..bf85733597ec 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -565,8 +565,8 @@ struct pmu {
 
         int                             *pmu_disable_count;
 
-        void (*pmu_enable)              (struct pmu *pmu);
-        void (*pmu_disable)             (struct pmu *pmu);
+        void (*pmu_enable)              (struct pmu *pmu); /* optional */
+        void (*pmu_disable)             (struct pmu *pmu); /* optional */
 
         /*
          * Should return -ENOENT when the @event doesn't match this PMU.
@@ -590,19 +590,19 @@ struct pmu {
          * Start the transaction, after this ->enable() doesn't need to
          * do schedulability tests.
          */
-        void (*start_txn)       (struct pmu *pmu);
+        void (*start_txn)       (struct pmu *pmu); /* optional */
         /*
          * 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)      (struct pmu *pmu);
+        int  (*commit_txn)      (struct pmu *pmu); /* optional */
         /*
          * Will cancel the transaction, assumes ->disable() is called
          * for each successfull ->enable() during the transaction.
          */
-        void (*cancel_txn)      (struct pmu *pmu);
+        void (*cancel_txn)      (struct pmu *pmu); /* optional */
 };
 
 /**
diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 5ed0c06765bb..8ef4ba3bcb1f 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -674,21 +674,14 @@ group_sched_in(struct perf_event *group_event,
 {
         struct perf_event *event, *partial_group = NULL;
         struct pmu *pmu = group_event->pmu;
-        bool txn = false;
 
         if (group_event->state == PERF_EVENT_STATE_OFF)
                 return 0;
 
-        /* Check if group transaction availabe */
-        if (pmu->start_txn)
-                txn = true;
-
-        if (txn)
-                pmu->start_txn(pmu);
+        pmu->start_txn(pmu);
 
         if (event_sched_in(group_event, cpuctx, ctx)) {
-                if (txn)
-                        pmu->cancel_txn(pmu);
+                pmu->cancel_txn(pmu);
                 return -EAGAIN;
         }
 
@@ -702,7 +695,7 @@ group_sched_in(struct perf_event *group_event,
                 }
         }
 
-        if (!txn || !pmu->commit_txn(pmu))
+        if (!pmu->commit_txn(pmu))
                 return 0;
 
 group_error:
@@ -717,8 +710,7 @@ group_error:
         }
         event_sched_out(group_event, cpuctx, ctx);
 
-        if (txn)
-                pmu->cancel_txn(pmu);
+        pmu->cancel_txn(pmu);
 
         return -EAGAIN;
 }
@@ -4965,6 +4957,31 @@ static LIST_HEAD(pmus);
 static DEFINE_MUTEX(pmus_lock);
 static struct srcu_struct pmus_srcu;
 
+static void perf_pmu_nop_void(struct pmu *pmu)
+{
+}
+
+static int perf_pmu_nop_int(struct pmu *pmu)
+{
+        return 0;
+}
+
+static void perf_pmu_start_txn(struct pmu *pmu)
+{
+        perf_pmu_disable(pmu);
+}
+
+static int perf_pmu_commit_txn(struct pmu *pmu)
+{
+        perf_pmu_enable(pmu);
+        return 0;
+}
+
+static void perf_pmu_cancel_txn(struct pmu *pmu)
+{
+        perf_pmu_enable(pmu);
+}
+
 int perf_pmu_register(struct pmu *pmu)
 {
         int ret;
@@ -4974,6 +4991,29 @@ int perf_pmu_register(struct pmu *pmu)
         pmu->pmu_disable_count = alloc_percpu(int);
         if (!pmu->pmu_disable_count)
                 goto unlock;
+
+        if (!pmu->start_txn) {
+                if (pmu->pmu_enable) {
+                        /*
+                         * If we have pmu_enable/pmu_disable calls, install
+                         * transaction stubs that use that to try and batch
+                         * hardware accesses.
+                         */
+                        pmu->start_txn  = perf_pmu_start_txn;
+                        pmu->commit_txn = perf_pmu_commit_txn;
+                        pmu->cancel_txn = perf_pmu_cancel_txn;
+                } else {
+                        pmu->start_txn  = perf_pmu_nop_void;
+                        pmu->commit_txn = perf_pmu_nop_int;
+                        pmu->cancel_txn = perf_pmu_nop_void;
+                }
+        }
+
+        if (!pmu->pmu_enable) {
+                pmu->pmu_enable  = perf_pmu_nop_void;
+                pmu->pmu_disable = perf_pmu_nop_void;
+        }
+
         list_add_rcu(&pmu->entry, &pmus);
         ret = 0;
 unlock: