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authorIngo Molnar <mingo@kernel.org>2013-09-03 07:41:11 +0200
committerIngo Molnar <mingo@kernel.org>2013-09-03 07:41:11 +0200
commit7d992feb7694a21ee81f22894b455dadd5d1c110 (patch)
treed0f0961186b1c31c536a26a7f986ad7ca677453b /include/linux/ftrace_event.h
parent6e4664525b1db28f8c4e1130957f70a94c19213e (diff)
parent25f27ce4a6a4995c8bdd69b4b2180465ed5ad2b8 (diff)
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Merge branch 'rcu/next' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu into core/rcu
Pull RCU updates from Paul E. McKenney: " * Update RCU documentation. These were posted to LKML at https://lkml.org/lkml/2013/8/19/611. * Miscellaneous fixes. These were posted to LKML at https://lkml.org/lkml/2013/8/19/619. * Full-system idle detection. This is for use by Frederic Weisbecker's adaptive-ticks mechanism. Its purpose is to allow the timekeeping CPU to shut off its tick when all other CPUs are idle. These were posted to LKML at https://lkml.org/lkml/2013/8/19/648. * Improve rcutorture test coverage. These were posted to LKML at https://lkml.org/lkml/2013/8/19/675. " Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'include/linux/ftrace_event.h')
-rw-r--r--include/linux/ftrace_event.h34
1 files changed, 34 insertions, 0 deletions
diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
index 120d57a1c3a5..5eaa746735ff 100644
--- a/include/linux/ftrace_event.h
+++ b/include/linux/ftrace_event.h
@@ -359,6 +359,40 @@ do { \
__trace_printk(ip, fmt, ##args); \
} while (0)
+/**
+ * tracepoint_string - register constant persistent string to trace system
+ * @str - a constant persistent string that will be referenced in tracepoints
+ *
+ * If constant strings are being used in tracepoints, it is faster and
+ * more efficient to just save the pointer to the string and reference
+ * that with a printf "%s" instead of saving the string in the ring buffer
+ * and wasting space and time.
+ *
+ * The problem with the above approach is that userspace tools that read
+ * the binary output of the trace buffers do not have access to the string.
+ * Instead they just show the address of the string which is not very
+ * useful to users.
+ *
+ * With tracepoint_string(), the string will be registered to the tracing
+ * system and exported to userspace via the debugfs/tracing/printk_formats
+ * file that maps the string address to the string text. This way userspace
+ * tools that read the binary buffers have a way to map the pointers to
+ * the ASCII strings they represent.
+ *
+ * The @str used must be a constant string and persistent as it would not
+ * make sense to show a string that no longer exists. But it is still fine
+ * to be used with modules, because when modules are unloaded, if they
+ * had tracepoints, the ring buffers are cleared too. As long as the string
+ * does not change during the life of the module, it is fine to use
+ * tracepoint_string() within a module.
+ */
+#define tracepoint_string(str) \
+ ({ \
+ static const char *___tp_str __tracepoint_string = str; \
+ ___tp_str; \
+ })
+#define __tracepoint_string __attribute__((section("__tracepoint_str")))
+
#ifdef CONFIG_PERF_EVENTS
struct perf_event;