[patch 26/26] Linux Kernel Markers - Use Immediate Values

From: Mathieu Desnoyers
Date: Thu Jan 24 2008 - 15:34:28 EST

Make markers use immediate values.

Changelog :
- Use imv_* instead of immediate_*.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx>
---
Documentation/markers.txt | 17 +++++++++++++----
include/linux/marker.h | 42 ++++++++++++++++++++++++++++++++----------
kernel/marker.c | 8 ++++++--
kernel/module.c | 1 +
4 files changed, 52 insertions(+), 16 deletions(-)

Index: linux-2.6-lttng.mm/include/linux/marker.h
===================================================================
--- linux-2.6-lttng.mm.orig/include/linux/marker.h 2008-01-24 14:40:50.000000000 -0500
+++ linux-2.6-lttng.mm/include/linux/marker.h 2008-01-24 14:44:30.000000000 -0500
@@ -12,6 +12,7 @@
* See the file COPYING for more details.
*/

+#include <linux/immediate.h>
#include <linux/types.h>

struct module;
@@ -42,7 +43,7 @@ struct marker {
const char *format; /* Marker format string, describing the
* variable argument list.
*/
- char state; /* Marker state. */
+ DEFINE_IMV(char, state);/* Immediate value state. */
char ptype; /* probe type : 0 : single, 1 : multi */
void (*call)(const struct marker *mdata, /* Probe wrapper */
void *call_private, const char *fmt, ...);
@@ -53,13 +54,14 @@ struct marker {
#ifdef CONFIG_MARKERS

/*
+ * Generic marker flavor always available.
* Note : the empty asm volatile with read constraint is used here instead of a
* "used" attribute to fix a gcc 4.1.x bug.
* Make sure the alignment of the structure in the __markers section will
* not add unwanted padding between the beginning of the section and the
* structure. Force alignment to the same alignment as the section start.
*/
-#define __trace_mark(name, call_private, format, args...) \
+#define __trace_mark(generic, name, call_private, format, args...) \
do { \
static const char __mstrtab_##name[] \
__attribute__((section("__markers_strings"))) \
@@ -70,17 +72,23 @@ struct marker {
0, 0, marker_probe_cb, \
{ __mark_empty_function, NULL}, NULL }; \
__mark_check_format(format, ## args); \
- if (unlikely(__mark_##name.state)) { \
- (*__mark_##name.call) \
- (&__mark_##name, call_private, \
- format, ## args); \
+ if (!generic) { \
+ if (unlikely(imv_read(__mark_##name.state))) \
+ (*__mark_##name.call) \
+ (&__mark_##name, call_private, \
+ format, ## args); \
+ } else { \
+ if (unlikely(_imv_read(__mark_##name.state))) \
+ (*__mark_##name.call) \
+ (&__mark_##name, call_private, \
+ format, ## args); \
} \
} while (0)

extern void marker_update_probe_range(struct marker *begin,
struct marker *end);
#else /* !CONFIG_MARKERS */
-#define __trace_mark(name, call_private, format, args...) \
+#define __trace_mark(generic, name, call_private, format, args...) \
__mark_check_format(format, ## args)
static inline void marker_update_probe_range(struct marker *begin,
struct marker *end)
@@ -88,15 +96,29 @@ static inline void marker_update_probe_r
#endif /* CONFIG_MARKERS */

/**
- * trace_mark - Marker
+ * trace_mark - Marker using code patching
* @name: marker name, not quoted.
* @format: format string
* @args...: variable argument list
*
- * Places a marker.
+ * Places a marker using optimized code patching technique (imv_read())
+ * to be enabled.
*/
#define trace_mark(name, format, args...) \
- __trace_mark(name, NULL, format, ## args)
+ __trace_mark(0, name, NULL, format, ## args)
+
+/**
+ * _trace_mark - Marker using variable read
+ * @name: marker name, not quoted.
+ * @format: format string
+ * @args...: variable argument list
+ *
+ * Places a marker using a standard memory read (_imv_read()) to be
+ * enabled. Should be used for markers in __init and __exit functions and in
+ * lockdep code.
+ */
+#define _trace_mark(name, format, args...) \
+ __trace_mark(1, name, NULL, format, ## args)

/**
* MARK_NOARGS - Format string for a marker with no argument.
Index: linux-2.6-lttng.mm/kernel/marker.c
===================================================================
--- linux-2.6-lttng.mm.orig/kernel/marker.c 2008-01-24 14:40:50.000000000 -0500
+++ linux-2.6-lttng.mm/kernel/marker.c 2008-01-24 14:44:30.000000000 -0500
@@ -23,6 +23,7 @@
#include <linux/rcupdate.h>
#include <linux/marker.h>
#include <linux/err.h>
+#include <linux/immediate.h>

extern struct marker __start___markers[];
extern struct marker __stop___markers[];
@@ -544,7 +545,7 @@ static int set_marker(struct marker_entr
*/
smp_wmb();
elem->ptype = (*entry)->ptype;
- elem->state = active;
+ elem->state__imv = active;

return 0;
}
@@ -558,7 +559,7 @@ static int set_marker(struct marker_entr
static void disable_marker(struct marker *elem)
{
/* leave "call" as is. It is known statically. */
- elem->state = 0;
+ elem->state__imv = 0;
elem->single.func = __mark_empty_function;
/* Update the function before setting the ptype */
smp_wmb();
@@ -625,6 +626,9 @@ static void marker_update_probes(void)
marker_update_probe_range(__start___markers, __stop___markers);
/* Markers in modules. */
module_update_markers();
+ /* Update immediate values */
+ core_imv_update();
+ module_imv_update();
}

/**
Index: linux-2.6-lttng.mm/Documentation/markers.txt
===================================================================
--- linux-2.6-lttng.mm.orig/Documentation/markers.txt 2008-01-24 14:09:00.000000000 -0500
+++ linux-2.6-lttng.mm/Documentation/markers.txt 2008-01-24 14:44:30.000000000 -0500
@@ -15,10 +15,12 @@ provide at runtime. A marker can be "on"
(no probe is attached). When a marker is "off" it has no effect, except for
adding a tiny time penalty (checking a condition for a branch) and space
penalty (adding a few bytes for the function call at the end of the
-instrumented function and adds a data structure in a separate section). When a
-marker is "on", the function you provide is called each time the marker is
-executed, in the execution context of the caller. When the function provided
-ends its execution, it returns to the caller (continuing from the marker site).
+instrumented function and adds a data structure in a separate section). The
+immediate values are used to minimize the impact on data cache, encoding the
+condition in the instruction stream. When a marker is "on", the function you
+provide is called each time the marker is executed, in the execution context of
+the caller. When the function provided ends its execution, it returns to the
+caller (continuing from the marker site).

You can put markers at important locations in the code. Markers are
lightweight hooks that can pass an arbitrary number of parameters,
@@ -69,6 +71,13 @@ a printk warning which identifies the in
"Format mismatch for probe probe_name (format), marker (format)"


+* Optimization for a given architecture
+
+To force use of a non-optimized version of the markers, _trace_mark() should be
+used. It takes the same parameters as the normal markers, but it does not use
+the immediate values based on code patching.
+
+
* Probe / marker example

See the example provided in samples/markers/src
Index: linux-2.6-lttng.mm/kernel/module.c
===================================================================
--- linux-2.6-lttng.mm.orig/kernel/module.c 2008-01-24 14:41:09.000000000 -0500
+++ linux-2.6-lttng.mm/kernel/module.c 2008-01-24 14:44:30.000000000 -0500
@@ -2002,6 +2002,7 @@ static struct module *load_module(void _
mod->markers + mod->num_markers);
#endif
#ifdef CONFIG_IMMEDIATE
+ /* Immediate values must be updated after markers */
imv_update_range(mod->immediate,
mod->immediate + mod->num_immediate);
#endif

--
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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