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authorIngo Molnar <mingo@elte.hu>2009-02-26 18:47:11 +0100
committerIngo Molnar <mingo@elte.hu>2009-02-26 18:44:06 +0100
commit14131f2f98ac350ee9e73faed916d2238a8b6a0d (patch)
treebf490d104276142e914f1245bbc9f44cb0d2bc9b /kernel/trace/trace_clock.c
parent6409c4da289d6905f7ae2bd0630438368439bda2 (diff)
downloadop-kernel-dev-14131f2f98ac350ee9e73faed916d2238a8b6a0d.zip
op-kernel-dev-14131f2f98ac350ee9e73faed916d2238a8b6a0d.tar.gz
tracing: implement trace_clock_*() APIs
Impact: implement new tracing timestamp APIs Add three trace clock variants, with differing scalability/precision tradeoffs: - local: CPU-local trace clock - medium: scalable global clock with some jitter - global: globally monotonic, serialized clock Make the ring-buffer use the local trace clock internally. Acked-by: Peter Zijlstra <peterz@infradead.org> Acked-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/trace/trace_clock.c')
-rw-r--r--kernel/trace/trace_clock.c101
1 files changed, 101 insertions, 0 deletions
diff --git a/kernel/trace/trace_clock.c b/kernel/trace/trace_clock.c
new file mode 100644
index 0000000..2d4953f
--- /dev/null
+++ b/kernel/trace/trace_clock.c
@@ -0,0 +1,101 @@
+/*
+ * tracing clocks
+ *
+ * Copyright (C) 2009 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
+ *
+ * Implements 3 trace clock variants, with differing scalability/precision
+ * tradeoffs:
+ *
+ * - local: CPU-local trace clock
+ * - medium: scalable global clock with some jitter
+ * - global: globally monotonic, serialized clock
+ *
+ * Tracer plugins will chose a default from these clocks.
+ */
+#include <linux/spinlock.h>
+#include <linux/hardirq.h>
+#include <linux/module.h>
+#include <linux/percpu.h>
+#include <linux/sched.h>
+#include <linux/ktime.h>
+
+/*
+ * trace_clock_local(): the simplest and least coherent tracing clock.
+ *
+ * Useful for tracing that does not cross to other CPUs nor
+ * does it go through idle events.
+ */
+u64 notrace trace_clock_local(void)
+{
+ /*
+ * sched_clock() is an architecture implemented, fast, scalable,
+ * lockless clock. It is not guaranteed to be coherent across
+ * CPUs, nor across CPU idle events.
+ */
+ return sched_clock();
+}
+
+/*
+ * trace_clock(): 'inbetween' trace clock. Not completely serialized,
+ * but not completely incorrect when crossing CPUs either.
+ *
+ * This is based on cpu_clock(), which will allow at most ~1 jiffy of
+ * jitter between CPUs. So it's a pretty scalable clock, but there
+ * can be offsets in the trace data.
+ */
+u64 notrace trace_clock(void)
+{
+ return cpu_clock(raw_smp_processor_id());
+}
+
+
+/*
+ * trace_clock_global(): special globally coherent trace clock
+ *
+ * It has higher overhead than the other trace clocks but is still
+ * an order of magnitude faster than GTOD derived hardware clocks.
+ *
+ * Used by plugins that need globally coherent timestamps.
+ */
+
+static u64 prev_trace_clock_time;
+
+static raw_spinlock_t trace_clock_lock ____cacheline_aligned_in_smp =
+ (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED;
+
+u64 notrace trace_clock_global(void)
+{
+ unsigned long flags;
+ int this_cpu;
+ u64 now;
+
+ raw_local_irq_save(flags);
+
+ this_cpu = raw_smp_processor_id();
+ now = cpu_clock(this_cpu);
+ /*
+ * If in an NMI context then dont risk lockups and return the
+ * cpu_clock() time:
+ */
+ if (unlikely(in_nmi()))
+ goto out;
+
+ __raw_spin_lock(&trace_clock_lock);
+
+ /*
+ * TODO: if this happens often then maybe we should reset
+ * my_scd->clock to prev_trace_clock_time+1, to make sure
+ * we start ticking with the local clock from now on?
+ */
+ if ((s64)(now - prev_trace_clock_time) < 0)
+ now = prev_trace_clock_time + 1;
+
+ prev_trace_clock_time = now;
+
+ __raw_spin_unlock(&trace_clock_lock);
+
+ out:
+ raw_local_irq_restore(flags);
+
+ return now;
+}
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