Messages in this thread Patch in this message | | | Date | Fri, 5 Aug 2016 16:35:55 +0200 | From | Sebastian Andrzej Siewior <> | Subject | Re: [RFC][PATCH 4/3] tracing: Add NMI tracing in hwlat detector |
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* Steven Rostedt | 2016-08-04 13:16:45 [-0400]:
>diff --git a/include/linux/ftrace_irq.h b/include/linux/ftrace_irq.h >index dca7bf8cffe2..4ec2c9b205f2 100644 >--- a/include/linux/ftrace_irq.h >+++ b/include/linux/ftrace_irq.h >@@ -3,11 +3,34 @@ … >+static inline void ftrace_nmi_enter(void) >+{ >+#ifdef CONFIG_HWLAT_TRACER >+ if (trace_hwlat_callback_enabled) >+ trace_hwlat_callback(true);
so we take a tracepoint while we enter an nmi
>--- a/kernel/trace/trace_hwlat.c >+++ b/kernel/trace/trace_hwlat.c >@@ -64,6 +64,15 @@ static struct dentry *hwlat_sample_window; /* sample window us */ > /* Save the previous tracing_thresh value */ > static unsigned long save_tracing_thresh; > >+/* NMI timestamp counters */ >+static u64 nmi_ts_start; >+static u64 nmi_total_ts; >+static int nmi_count; >+static int nmi_cpu;
and this is always limited to one CPU at a time?
… >@@ -125,6 +138,19 @@ static void trace_hwlat_sample(struct hwlat_sample *sample) > #define init_time(a, b) (a = b) > #define time_u64(a) a > >+void trace_hwlat_callback(bool enter) >+{ >+ if (smp_processor_id() != nmi_cpu) >+ return; >+ >+ if (enter) >+ nmi_ts_start = time_get();
but more interestingly: trace_clock_local() -> sched_clock() and of kernel/time/sched_clock.c we do raw_read_seqcount(&cd.seq) which means we are busted if the NMI triggers during update_clock_read_data().
>+ else { >+ nmi_total_ts = time_get() - nmi_ts_start; >+ nmi_count++; >+ } >+}
Sebastian
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