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Message-ID: <20140220100830.GN6835@laptop.programming.kicks-ass.net>
Date: Thu, 20 Feb 2014 11:08:30 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Vince Weaver <vincent.weaver@...ne.edu>
Cc: Dave Jones <davej@...hat.com>,
Linux Kernel <linux-kernel@...r.kernel.org>,
Ingo Molnar <mingo@...hat.com>,
Paul Mackerras <paulus@...ba.org>,
Steven Rostedt <rostedt@...dmis.org>
Subject: Re: x86_pmu_start WARN_ON.
On Wed, Feb 19, 2014 at 05:34:49PM -0500, Vince Weaver wrote:
> So where would the NMI counter event get disabled? Would it never get
> disabled, just because it's always running and always gets the same fixed
> slot? Why isn't this a problem all the time, not just with corner cases?
Well it could get another counter assignment I suppose; there's no
guarantee it always ends up in the fixed counter although that's rather
likely.
> Is somehow n_added getting confused?
I'd expect worse than a warning if that happened, but who knows.
You could try with the below; make sure you've got CONFIG_FUNCTION_TRACER=y.
Then (assuming debugfs is mounted in /debug ; most modern distros have
it at /sys/kernel/debug but they're wrong!):
# echo 0 > /debug/tracing/tracing_on
# echo function > /debug/tracing/current_tracer
# echo nop > /debug/tracing/current_tracer
# echo 0 > /debug/tracing/trace
# echo 1 > /debug/tracing/tracing_on
And make it go *BOOM*, then:
# cat /debug/tracing/trace | bzip2 -9 > ~/trace.bz2
And send that (and look at it of course).
@rostedt: WTF is disable_trace_on_warning a boot option only?
---
arch/x86/kernel/cpu/perf_event.c | 65 +++++++++++++++++++++++++++++++++++++++-
1 file changed, 64 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index 895604f2e916..d3edf301deb8 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -509,6 +509,42 @@ void x86_pmu_disable_all(void)
}
}
+static void x86_pmu_state(struct pmu *pmu)
+{
+ struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);
+ int i;
+
+ trace_printk("Events: {\n");
+ for (i = 0; i < X86_PMC_IDX_MAX; i++) {
+ struct perf_event *event = cpuc->events[i];
+ int active = test_bit(i, cpuc->active_mask);
+ int running = test_bit(i, cpuc->running);
+
+ if (active || running) {
+ trace_printk(" %d: state: %c%c config: %lx (%p)\n",
+ i, active ? 'A' : '.',
+ running ? 'R' : '.',
+ event ? event->attr.config : -1L,
+ event);
+ }
+ }
+ trace_printk("}\n");
+
+
+ trace_printk("n_events: %d, n_added: %d, n_txn: %d\n",
+ cpuc->n_events, cpuc->n_added, cpuc->n_txn);
+ trace_printk("Assignment: {\n");
+ for (i = 0; i < cpuc->n_events; i++) {
+ struct perf_event *event = cpuc->event_list[i];
+
+ trace_printk(" %d->%d tag: %lx config: %lx (%p)\n",
+ i, cpuc->assign[i], cpuc->tags[i],
+ event ? event->attr.config : -1L,
+ event);
+ }
+ trace_printk("}\n");
+}
+
static void x86_pmu_disable(struct pmu *pmu)
{
struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);
@@ -524,6 +560,9 @@ static void x86_pmu_disable(struct pmu *pmu)
barrier();
x86_pmu.disable_all();
+
+ trace_printk("x86_pmu_disable\n");
+ x86_pmu_state(pmu);
}
void x86_pmu_enable_all(int added)
@@ -820,6 +859,7 @@ static int collect_events(struct cpu_hw_events *cpuc, struct perf_event *leader,
return -EINVAL;
cpuc->event_list[n] = leader;
n++;
+ trace_printk("Adding event: %lx (%p)\n", leader->attr.config, leader);
}
if (!dogrp)
return n;
@@ -834,6 +874,7 @@ static int collect_events(struct cpu_hw_events *cpuc, struct perf_event *leader,
cpuc->event_list[n] = event;
n++;
+ trace_printk("Adding event: %lx (%p)\n", event->attr.config, event);
}
return n;
}
@@ -885,6 +926,9 @@ static void x86_pmu_enable(struct pmu *pmu)
if (cpuc->enabled)
return;
+ trace_printk("x86_pmu_enable\n");
+ x86_pmu_state(pmu);
+
if (cpuc->n_added) {
int n_running = cpuc->n_events - cpuc->n_added;
/*
@@ -898,6 +942,11 @@ static void x86_pmu_enable(struct pmu *pmu)
event = cpuc->event_list[i];
hwc = &event->hw;
+ trace_printk("K%d: hwc->idx: %d, hwc->last_cpu: %d,"
+ " hwc->last_tag: %lx hwc->state: %x\n",
+ i, hwc->idx, hwc->last_cpu,
+ hwc->last_tag, hwc->state);
+
/*
* we can avoid reprogramming counter if:
* - assigned same counter as last time
@@ -915,6 +964,8 @@ static void x86_pmu_enable(struct pmu *pmu)
if (hwc->state & PERF_HES_STOPPED)
hwc->state |= PERF_HES_ARCH;
+ trace_printk("stopping: %d\n", i);
+
x86_pmu_stop(event, PERF_EF_UPDATE);
}
@@ -922,6 +973,11 @@ static void x86_pmu_enable(struct pmu *pmu)
event = cpuc->event_list[i];
hwc = &event->hw;
+ trace_printk("S%d: hwc->idx: %d, hwc->last_cpu: %d,"
+ " hwc->last_tag: %lx hwc->state: %x\n",
+ i, hwc->idx, hwc->last_cpu,
+ hwc->last_tag, hwc->state);
+
if (!match_prev_assignment(hwc, cpuc, i))
x86_assign_hw_event(event, cpuc, i);
else if (i < n_running)
@@ -930,12 +986,17 @@ static void x86_pmu_enable(struct pmu *pmu)
if (hwc->state & PERF_HES_ARCH)
continue;
+ trace_printk("starting: %d\n", i);
+
x86_pmu_start(event, PERF_EF_RELOAD);
}
cpuc->n_added = 0;
perf_events_lapic_init();
}
+ x86_pmu_state(pmu);
+ trace_printk("x86_pmu_enabled\n");
+
cpuc->enabled = 1;
barrier();
@@ -1073,8 +1134,10 @@ static void x86_pmu_start(struct perf_event *event, int flags)
struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);
int idx = event->hw.idx;
- if (WARN_ON_ONCE(!(event->hw.state & PERF_HES_STOPPED)))
+ if (WARN_ON_ONCE(!(event->hw.state & PERF_HES_STOPPED))) {
+ tracing_off();
return;
+ }
if (WARN_ON_ONCE(idx == -1))
return;
--
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