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Message-ID: <4cbe1191.8709d80a.1d10.ffff9970@mx.google.com>
Date: Tue, 19 Oct 2010 23:45:01 +0200
From: Stephane Eranian <eranian@...gle.com>
To: linux-kernel@...r.kernel.org
Cc: peterz@...radead.org, mingo@...e.hu, paulus@...ba.org,
davem@...emloft.net, fweisbec@...il.com,
perfmon2-devel@...ts.sf.net, eranian@...il.com, eranian@...gle.com,
robert.richter@....com
Subject: [PATCH] perf_events: fix the fix for transaction recovery in group_sched_in()
This patch fixes the group_sched_in() fix added by commit 8e5fc1a.
Although the patch solved the issue with time_running, time_enabled
for all events in a group, it had one flaw in case the group could
never be scheduled. It would cause time_enabled to get negative.
The issue was that tstamp_stopped was never updated, even though
tstamp_enabled was.
This new version is much simpler and ensures that in case of
error in group_sched_in() during event_sched_in(), the events up
to the failed event go through regular event_sched_out(). But the
failed event and the remaining events in the group have their timings
adjusted as if they had also gone through event_sched_in() and
event_sched_out(). This ensures timing uniformity across all
events in a group. This also takes care of the tstamp_stopped problem
in case the group could never be scheduled. The tstamp_stopped is
updated as if the event had actually run.
With this patch, the following now reports correct time_enabled,
in case the NMI watchdog is active:
$ task -e unhalted_core_cycles,instructions_retired,baclears,baclears noploop 1
noploop for 1 seconds
0 unhalted_core_cycles (100.00% scaling, ena=997,552,872, run=0)
0 instructions_retired (100.00% scaling, ena=997,552,872, run=0)
0 baclears (100.00% scaling, ena=997,552,872, run=0)
0 baclears (100.00% scaling, ena=997,552,872, run=0)
And the older test case also works:
$ task -einstructions_retired,baclears,baclears -e unhalted_core_cycles,baclears,baclears sleep 5
1680885 instructions_retired (69.39% scaling, ena=950756, run=291006)
10735 baclears (69.39% scaling, ena=950756, run=291006)
10735 baclears (69.39% scaling, ena=950756, run=291006)
0 unhalted_core_cycles (100.00% scaling, ena=817932, run=0)
0 baclears (100.00% scaling, ena=817932, run=0)
0 baclears (100.00% scaling, ena=817932, run=0)
Signed-off-by: Stephane Eranian <eranian@...gle.com>
---
diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index f309e80..8e5841d 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -418,7 +418,7 @@ event_filter_match(struct perf_event *event)
}
static int
-__event_sched_out(struct perf_event *event,
+event_sched_out(struct perf_event *event,
struct perf_cpu_context *cpuctx,
struct perf_event_context *ctx)
{
@@ -447,6 +447,8 @@ __event_sched_out(struct perf_event *event,
event->pmu->del(event, 0);
event->oncpu = -1;
+ event->tstamp_stopped = ctx->time;
+
if (!is_software_event(event))
cpuctx->active_oncpu--;
ctx->nr_active--;
@@ -456,18 +458,6 @@ __event_sched_out(struct perf_event *event,
}
static void
-event_sched_out(struct perf_event *event,
- struct perf_cpu_context *cpuctx,
- struct perf_event_context *ctx)
-{
- int ret;
-
- ret = __event_sched_out(event, cpuctx, ctx);
- if (ret)
- event->tstamp_stopped = ctx->time;
-}
-
-static void
group_sched_out(struct perf_event *group_event,
struct perf_cpu_context *cpuctx,
struct perf_event_context *ctx)
@@ -664,7 +654,7 @@ retry:
}
static int
-__event_sched_in(struct perf_event *event,
+event_sched_in(struct perf_event *event,
struct perf_cpu_context *cpuctx,
struct perf_event_context *ctx)
{
@@ -684,6 +674,8 @@ __event_sched_in(struct perf_event *event,
return -EAGAIN;
}
+ event->tstamp_running += ctx->time - event->tstamp_stopped;
+
if (!is_software_event(event))
cpuctx->active_oncpu++;
ctx->nr_active++;
@@ -694,35 +686,6 @@ __event_sched_in(struct perf_event *event,
return 0;
}
-static inline int
-event_sched_in(struct perf_event *event,
- struct perf_cpu_context *cpuctx,
- struct perf_event_context *ctx)
-{
- int ret = __event_sched_in(event, cpuctx, ctx);
- if (ret)
- return ret;
- event->tstamp_running += ctx->time - event->tstamp_stopped;
- return 0;
-}
-
-static void
-group_commit_event_sched_in(struct perf_event *group_event,
- struct perf_cpu_context *cpuctx,
- struct perf_event_context *ctx)
-{
- struct perf_event *event;
- u64 now = ctx->time;
-
- group_event->tstamp_running += now - group_event->tstamp_stopped;
- /*
- * Schedule in siblings as one group (if any):
- */
- list_for_each_entry(event, &group_event->sibling_list, group_entry) {
- event->tstamp_running += now - event->tstamp_stopped;
- }
-}
-
static int
group_sched_in(struct perf_event *group_event,
struct perf_cpu_context *cpuctx,
@@ -730,19 +693,15 @@ group_sched_in(struct perf_event *group_event,
{
struct perf_event *event, *partial_group = NULL;
struct pmu *pmu = group_event->pmu;
+ bool simulate = false;
+ u64 now = ctx->time;
if (group_event->state == PERF_EVENT_STATE_OFF)
return 0;
pmu->start_txn(pmu);
- /*
- * use __event_sched_in() to delay updating tstamp_running
- * until the transaction is committed. In case of failure
- * we will keep an unmodified tstamp_running which is a
- * requirement to get correct timing information
- */
- if (__event_sched_in(group_event, cpuctx, ctx)) {
+ if (event_sched_in(group_event, cpuctx, ctx)) {
pmu->cancel_txn(pmu);
return -EAGAIN;
}
@@ -751,31 +710,43 @@ group_sched_in(struct perf_event *group_event,
* Schedule in siblings as one group (if any):
*/
list_for_each_entry(event, &group_event->sibling_list, group_entry) {
- if (__event_sched_in(event, cpuctx, ctx)) {
+ if (event_sched_in(event, cpuctx, ctx)) {
partial_group = event;
goto group_error;
}
}
- if (!pmu->commit_txn(pmu)) {
- /* commit tstamp_running */
- group_commit_event_sched_in(group_event, cpuctx, ctx);
+ if (!pmu->commit_txn(pmu))
return 0;
- }
group_error:
/*
* Groups can be scheduled in as one unit only, so undo any
* partial group before returning:
*
- * use __event_sched_out() to avoid updating tstamp_stopped
- * because the event never actually ran
+ * The events up to the failed event are scheduled out normally,
+ * tstamp_stopped will be updated.
+ *
+ * The failed events and the remaining siblings need to have
+ * their timings updated as if they had gone thru event_sched_in()
+ * and event_sched_out(). This is required to get consistent timings
+ * across the group. This also takes care of the case where the group
+ * could never be scheduled by ensuring tstamp_stopped is set to mark
+ * the time the event was actually stopped, such that time delta
+ * calculation in update_event_times() is correct.
*/
list_for_each_entry(event, &group_event->sibling_list, group_entry) {
+
if (event == partial_group)
- break;
- __event_sched_out(event, cpuctx, ctx);
+ simulate = true;
+
+ if (simulate) {
+ event->tstamp_running += now - event->tstamp_stopped;
+ event->tstamp_stopped = now;
+ } else {
+ event_sched_out(event, cpuctx, ctx);
+ }
}
- __event_sched_out(group_event, cpuctx, ctx);
+ event_sched_out(group_event, cpuctx, ctx);
pmu->cancel_txn(pmu);
--
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