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Date: Wed, 22 Jul 2015 14:22:08 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Vince Weaver <vincent.weaver@...ne.edu>
Cc: linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>
Subject: Re: perf: multiplexing broken on amd fam16h?
On Tue, Jul 21, 2015 at 04:08:28PM -0400, Vince Weaver wrote:
> On Tue, 21 Jul 2015, Peter Zijlstra wrote:
>
> > On Tue, Jul 21, 2015 at 02:14:54PM -0400, Vince Weaver wrote:
> > > Hello
> > >
> > > I have a new AMD A8 system and perf multiplexing support is acting weird.
> > >
> > > If I run the perf_event_tests check_multiplexing test it fails like this:
> > >
> > > Event TotalCount RawCount Scale ScaledCount Error
> > > 0 500282143 150403975 -2.00 (c8050b5 fffffffff9c224ef) -300807950 160.13%
> > >
> > > So the problem is that the TOTAL_TIME_RUNNING value is negative, which as
> > > far as I know shouldn't be possible.
> >
> > Correct, that should not happen. I don't have a Fam16 machine, but I can
> > try and stare at the code a wee bit. Although there's another few perf
> > issues I am still looking into as well :/
>
> well I've traced it back to see that in
> update_event_times()
> run_end is less than event->tstamp_running, which is why the result
> is negative.
>
> [ 1279.857205] VMW: 1 run_end=1279846999345 tstamp_running=1279929016607
> [ 1279.857222] VMW: 0 run_end=1279855184453 tstamp_running=1279931111760
>
> It seems to happen both in the PERF_EVENT_STATE_INACTIVE and
> !PERF_EVENT_STATE_INACTIVE cases.
>
> tracking back why those values are wrong is proving to be a bit trickier.
Can you run with something like the below?
---
kernel/events/core.c | 79 ++++++++++++++++++++++++++++++++++++++--------------
1 file changed, 58 insertions(+), 21 deletions(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index d3dae3419b99..cd96bb9b1c72 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -1115,15 +1115,26 @@ static void perf_unpin_context(struct perf_event_context *ctx)
raw_spin_unlock_irqrestore(&ctx->lock, flags);
}
+static void start_context_time(struct perf_event_context *ctx)
+{
+ u64 now = perf_clock();
+
+ ctx->timestamp = now;
+ trace_printk("ctx: %p now: %Lu\n", ctx, now);
+}
+
/*
* Update the record of the current time in a context.
*/
static void update_context_time(struct perf_event_context *ctx)
{
u64 now = perf_clock();
+ u64 delta = now - ctx->timestamp;
- ctx->time += now - ctx->timestamp;
+ ctx->time += delta;
ctx->timestamp = now;
+ trace_printk("ctx: %p now: %Lu time: %Lu delta: %Lu\n",
+ ctx, now, ctx->time, delta);
}
static u64 perf_event_time(struct perf_event *event)
@@ -1167,6 +1178,10 @@ static void update_event_times(struct perf_event *event)
event->total_time_enabled = run_end - event->tstamp_enabled;
+ trace_printk("event: %p time: %Lu stopped: %Lu end: %Lu enabled: %Lu\n",
+ event, ctx->time, event->tstamp_stopped,
+ run_end, event->tstamp_enabled);
+
if (event->state == PERF_EVENT_STATE_INACTIVE)
run_end = event->tstamp_stopped;
else
@@ -1174,6 +1189,9 @@ static void update_event_times(struct perf_event *event)
event->total_time_running = run_end - event->tstamp_running;
+ trace_printk("event: %p time: %Lu stopped: %Lu end: %Lu running: %Lu\n",
+ event, ctx->time, event->tstamp_stopped,
+ run_end, event->tstamp_running);
}
/*
@@ -1526,21 +1544,25 @@ event_sched_out(struct perf_event *event,
WARN_ON_ONCE(event->ctx != ctx);
lockdep_assert_held(&ctx->lock);
- /*
- * An event which could not be activated because of
- * filter mismatch still needs to have its timings
- * maintained, otherwise bogus information is return
- * via read() for time_enabled, time_running:
- */
- if (event->state == PERF_EVENT_STATE_INACTIVE
- && !event_filter_match(event)) {
- delta = tstamp - event->tstamp_stopped;
- event->tstamp_running += delta;
- event->tstamp_stopped = tstamp;
- }
+ if (event->state != PERF_EVENT_STATE_ACTIVE) {
+ /*
+ * An event which could not be activated because of
+ * filter mismatch still needs to have its timings
+ * maintained, otherwise bogus information is return
+ * via read() for time_enabled, time_running:
+ */
+ if (event->state == PERF_EVENT_STATE_INACTIVE &&
+ !event_filter_match(event)) {
+ delta = tstamp - event->tstamp_stopped;
+ event->tstamp_running += delta;
+ event->tstamp_stopped = tstamp;
+
+ trace_printk("event: %p filter-update: time: %Lu running: %Lu delta: %Lu\n",
+ event, tstamp, event->tstamp_running, delta);
+ }
- if (event->state != PERF_EVENT_STATE_ACTIVE)
return;
+ }
perf_pmu_disable(event->pmu);
@@ -1550,6 +1572,9 @@ event_sched_out(struct perf_event *event,
event->state = PERF_EVENT_STATE_OFF;
}
event->tstamp_stopped = tstamp;
+
+ trace_printk("event: %p time: %Lu\n", event, tstamp);
+
event->pmu->del(event, 0);
event->oncpu = -1;
@@ -1870,6 +1895,9 @@ event_sched_in(struct perf_event *event,
event->tstamp_running += tstamp - event->tstamp_stopped;
+ trace_printk("event: %p time: %Lu stopped: %Lu running: %Lu\n",
+ event, tstamp, event->tstamp_stopped, event->tstamp_running);
+
perf_set_shadow_time(event, ctx, tstamp);
perf_log_itrace_start(event);
@@ -1907,7 +1935,7 @@ group_sched_in(struct perf_event *group_event,
{
struct perf_event *event, *partial_group = NULL;
struct pmu *pmu = ctx->pmu;
- u64 now = ctx->time;
+ u64 tstamp = perf_event_time(group_event);
bool simulate = false;
if (group_event->state == PERF_EVENT_STATE_OFF)
@@ -1954,8 +1982,11 @@ group_sched_in(struct perf_event *group_event,
simulate = true;
if (simulate) {
- event->tstamp_running += now - event->tstamp_stopped;
- event->tstamp_stopped = now;
+ event->tstamp_running += tstamp - event->tstamp_stopped;
+ event->tstamp_stopped = tstamp;
+ trace_printk("event: %p simulate: time: %Lu running: %Lu stopped: %Lu\n",
+ event, tstamp, event->tstamp_running,
+ event->tstamp_stopped);
} else {
event_sched_out(event, cpuctx, ctx);
}
@@ -2010,6 +2041,7 @@ static void add_event_to_ctx(struct perf_event *event,
event->tstamp_enabled = tstamp;
event->tstamp_running = tstamp;
event->tstamp_stopped = tstamp;
+ trace_printk("event: %p time: %Lu\n", event, tstamp);
}
static void task_ctx_sched_out(struct perf_event_context *ctx);
@@ -2153,9 +2185,11 @@ perf_install_in_context(struct perf_event_context *ctx,
/*
* Put a event into inactive state and update time fields.
+ *
* Enabling the leader of a group effectively enables all
* the group members that aren't explicitly disabled, so we
* have to update their ->tstamp_enabled also.
+ *
* Note: this works for group members as well as group leaders
* since the non-leader members' sibling_lists will be empty.
*/
@@ -2166,9 +2200,14 @@ static void __perf_event_mark_enabled(struct perf_event *event)
event->state = PERF_EVENT_STATE_INACTIVE;
event->tstamp_enabled = tstamp - event->total_time_enabled;
+ trace_printk("event: %p time: %Lu enabled: %Lu\n",
+ event, tstamp, event->tstamp_enabled);
list_for_each_entry(sub, &event->sibling_list, group_entry) {
- if (sub->state >= PERF_EVENT_STATE_INACTIVE)
+ if (sub->state >= PERF_EVENT_STATE_INACTIVE) {
sub->tstamp_enabled = tstamp - sub->total_time_enabled;
+ trace_printk("event: %p time: %Lu enabled: %Lu\n",
+ sub, tstamp, sub->tstamp_enabled);
+ }
}
}
@@ -2741,15 +2780,13 @@ ctx_sched_in(struct perf_event_context *ctx,
enum event_type_t event_type,
struct task_struct *task)
{
- u64 now;
int is_active = ctx->is_active;
ctx->is_active |= event_type;
if (likely(!ctx->nr_events))
return;
- now = perf_clock();
- ctx->timestamp = now;
+ start_context_time(ctx);
perf_cgroup_set_timestamp(task, ctx);
/*
* First go through the list and put on any pinned groups
--
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