[RFC patch 24/41] Linux Kernel Markers - Use Immediate Values

Mathieu Desnoyers
2009-03-05T23:28:29Z

[-- Attachment #1: linux-kernel-markers-immediate-values.patch --]
[-- Type: text/plain, Size: 5580 bytes --]

Make markers use immediate values.

Changelog :
- Use imv_* instead of immediate_*.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
---
Documentation/markers.txt | 17 +++++++++++++----
include/linux/marker.h | 16 ++++++++++++----
kernel/marker.c | 12 ++++++++----
ltt/ltt-marker-control.c | 4 ++--
4 files changed, 35 insertions(+), 14 deletions(-)

Index: linux-2.6-lttng/include/linux/marker.h
===================================================================
--- linux-2.6-lttng.orig/include/linux/marker.h 2009-02-06 15:03:19.000000000 -0500
+++ linux-2.6-lttng/include/linux/marker.h 2009-02-06 15:17:46.000000000 -0500
@@ -14,6 +14,7 @@

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

struct module;
struct marker;
@@ -43,7 +44,7 @@ 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 */
/* Probe wrapper */
void (*call)(const struct marker *mdata, void *call_private, ...);
@@ -86,9 +87,16 @@ struct marker {
do { \
DEFINE_MARKER(name, format); \
__mark_check_format(format, ## args); \
- if (unlikely(__mark_##name.state)) { \
- (*__mark_##name.call) \
- (&__mark_##name, call_private, ## args);\
+ if (!generic) { \
+ if (unlikely(imv_read(__mark_##name.state))) \
+ (*__mark_##name.call) \
+ (&__mark_##name, call_private, \
+ ## args); \
+ } else { \
+ if (unlikely(_imv_read(__mark_##name.state))) \
+ (*__mark_##name.call) \
+ (&__mark_##name, call_private, \
+ ## args); \
} \
} while (0)

Index: linux-2.6-lttng/kernel/marker.c
===================================================================
--- linux-2.6-lttng.orig/kernel/marker.c 2009-02-06 15:03:19.000000000 -0500
+++ linux-2.6-lttng/kernel/marker.c 2009-02-06 15:17:46.000000000 -0500
@@ -24,6 +24,7 @@
#include <linux/marker.h>
#include <linux/err.h>
#include <linux/slab.h>
+#include <linux/immediate.h>

extern struct marker __start___markers[];
extern struct marker __stop___markers[];
@@ -532,7 +533,7 @@ static int set_marker(struct marker_entr
smp_wmb();
elem->ptype = entry->ptype;

- if (elem->tp_name && (active ^ elem->state)) {
+ if (elem->tp_name && (active ^ _imv_read(elem->state))) {
WARN_ON(!elem->tp_cb);
/*
* It is ok to directly call the probe registration because type
@@ -562,7 +563,7 @@ static int set_marker(struct marker_entr
(unsigned long)elem->tp_cb));
}
}
- elem->state = active;
+ elem->state__imv = active;

return ret;
}
@@ -578,7 +579,7 @@ static void disable_marker(struct marker
int ret;

/* leave "call" as is. It is known statically. */
- if (elem->tp_name && elem->state) {
+ if (elem->tp_name && _imv_read(elem->state)) {
WARN_ON(!elem->tp_cb);
/*
* It is ok to directly call the probe registration because type
@@ -593,7 +594,7 @@ static void disable_marker(struct marker
*/
module_put(__module_text_address((unsigned long)elem->tp_cb));
}
- elem->state = 0;
+ elem->state__imv = 0;
elem->single.func = __mark_empty_function;
/* Update the function before setting the ptype */
smp_wmb();
@@ -657,6 +658,9 @@ static void marker_update_probes(void)
/* Markers in modules. */
module_update_markers();
tracepoint_probe_update_all();
+ /* Update immediate values */
+ core_imv_update();
+ module_imv_update();
}

/**
Index: linux-2.6-lttng/Documentation/markers.txt
===================================================================
--- linux-2.6-lttng.orig/Documentation/markers.txt 2009-02-06 14:45:26.000000000 -0500
+++ linux-2.6-lttng/Documentation/markers.txt 2009-02-06 15:17:46.000000000 -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,
@@ -90,6 +92,13 @@ notrace void probe_tracepoint_name(unsig
/* write data to trace buffers ... */
}

+* 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