perf/core: Add a 'flags' parameter to the PMU transactional interfaces

Currently, the PMU interface allows reading only one counter at a time.
But some PMUs like the 24x7 counters in Power, support reading several
counters at once. To leveage this functionality, extend the transaction
interface to support a "transaction type".

The first type, PERF_PMU_TXN_ADD, refers to the existing transactions,
i.e. used to _schedule_ all the events on the PMU as a group. A second
transaction type, PERF_PMU_TXN_READ, will be used in a follow-on patch,
by the 24x7 counters to read several counters at once.

Extend the transaction interfaces to the PMU to accept a 'txn_flags'
parameter and use this parameter to ignore any transactions that are
not of type PERF_PMU_TXN_ADD.

Thanks to Peter Zijlstra for his input.

Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
[peterz: s390 compile fix]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Link: http://lkml.kernel.org/r/1441336073-22750-3-git-send-email-sukadev@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 28 insertions, 3 deletions

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 76e64be9bfb5..c80cee82959f 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -1914,7 +1914,7 @@ group_sched_in(struct perf_event *group_event,
         if (group_event->state == PERF_EVENT_STATE_OFF)
                 return 0;
 
-        pmu->start_txn(pmu);
+        pmu->start_txn(pmu, PERF_PMU_TXN_ADD);
 
         if (event_sched_in(group_event, cpuctx, ctx)) {
                 pmu->cancel_txn(pmu);
@@ -7267,24 +7267,49 @@ static void perf_pmu_nop_void(struct pmu *pmu)
 {
 }
 
+static void perf_pmu_nop_txn(struct pmu *pmu, unsigned int flags)
+{
+}
+
 static int perf_pmu_nop_int(struct pmu *pmu)
 {
         return 0;
 }
 
-static void perf_pmu_start_txn(struct pmu *pmu)
+DEFINE_PER_CPU(unsigned int, nop_txn_flags);
+
+static void perf_pmu_start_txn(struct pmu *pmu, unsigned int flags)
 {
+        __this_cpu_write(nop_txn_flags, flags);
+
+        if (flags & ~PERF_PMU_TXN_ADD)
+                return;
+
         perf_pmu_disable(pmu);
 }
 
 static int perf_pmu_commit_txn(struct pmu *pmu)
 {
+        unsigned int flags = __this_cpu_read(nop_txn_flags);
+
+        __this_cpu_write(nop_txn_flags, 0);
+
+        if (flags & ~PERF_PMU_TXN_ADD)
+                return 0;
+
         perf_pmu_enable(pmu);
         return 0;
 }
 
 static void perf_pmu_cancel_txn(struct pmu *pmu)
 {
+        unsigned int flags =  __this_cpu_read(nop_txn_flags);
+
+        __this_cpu_write(nop_txn_flags, 0);
+
+        if (flags & ~PERF_PMU_TXN_ADD)
+                return;
+
         perf_pmu_enable(pmu);
 }
 
@@ -7523,7 +7548,7 @@ got_cpu_context:
                         pmu->commit_txn = perf_pmu_commit_txn;
                         pmu->cancel_txn = perf_pmu_cancel_txn;
                 } else {
-                        pmu->start_txn  = perf_pmu_nop_void;
+                        pmu->start_txn  = perf_pmu_nop_txn;
                         pmu->commit_txn = perf_pmu_nop_int;
                         pmu->cancel_txn = perf_pmu_nop_void;
                 }