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Subject[RFC patch 18/27] Markers - remove extra format argument

Denys Vlasenko <vda.linux@googlemail.com> :

> Not in this patch, but I noticed:
>
> #define __trace_mark(name, call_private, format, args...) \
> do { \
> static const char __mstrtab_##name[] \
> __attribute__((section("__markers_strings"))) \
> = #name "\0" format; \
> static struct marker __mark_##name \
> __attribute__((section("__markers"), aligned(8))) = \
> { __mstrtab_##name, &__mstrtab_##name[sizeof(#name)], \
> 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); \
> } \
> } while (0)
>
> In this call:
>
> (*__mark_##name.call) \
> (&__mark_##name, call_private, \
> format, ## args); \
>
> you make gcc allocate duplicate format string. You can use
> &__mstrtab_##name[sizeof(#name)] instead since it holds the same string,
> or drop ", format," above and "const char *fmt" from here:
>
> void (*call)(const struct marker *mdata, /* Probe wrapper */
> void *call_private, const char *fmt, ...);
>
> since mdata->format is the same and all callees which need it can take it there.

Very good point. I actually thought about dropping it, since it would
remove an unnecessary argument from the stack. And actually, since I now
have the marker_probe_cb sitting between the marker site and the
callbacks, there is no API change required. Thanks :)

Mathieu

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
CC: Denys Vlasenko <vda.linux@googlemail.com>
---
include/linux/marker.h | 11 +++++------
kernel/marker.c | 30 ++++++++++++++----------------
2 files changed, 19 insertions(+), 22 deletions(-)
Index: linux-2.6-lttng/include/linux/marker.h
===================================================================
--- linux-2.6-lttng.orig/include/linux/marker.h 2008-03-27 20:51:34.000000000 -0400
+++ linux-2.6-lttng/include/linux/marker.h 2008-03-27 20:54:55.000000000 -0400
@@ -44,8 +44,8 @@ struct marker {
*/
char state; /* Marker state. */
char ptype; /* probe type : 0 : single, 1 : multi */
- void (*call)(const struct marker *mdata, /* Probe wrapper */
- void *call_private, const char *fmt, ...);
+ /* Probe wrapper */
+ void (*call)(const struct marker *mdata, void *call_private, ...);
struct marker_probe_closure single;
struct marker_probe_closure *multi;
} __attribute__((aligned(8)));
@@ -72,8 +72,7 @@ struct marker {
__mark_check_format(format, ## args); \
if (unlikely(__mark_##name.state)) { \
(*__mark_##name.call) \
- (&__mark_##name, call_private, \
- format, ## args); \
+ (&__mark_##name, call_private, ## args);\
} \
} while (0)

@@ -117,9 +116,9 @@ static inline void __printf(1, 2) ___mar
extern marker_probe_func __mark_empty_function;

extern void marker_probe_cb(const struct marker *mdata,
- void *call_private, const char *fmt, ...);
+ void *call_private, ...);
extern void marker_probe_cb_noarg(const struct marker *mdata,
- void *call_private, const char *fmt, ...);
+ void *call_private, ...);

/*
* Connect a probe to a marker.
Index: linux-2.6-lttng/kernel/marker.c
===================================================================
--- linux-2.6-lttng.orig/kernel/marker.c 2008-03-27 20:52:09.000000000 -0400
+++ linux-2.6-lttng/kernel/marker.c 2008-03-27 20:56:13.000000000 -0400
@@ -54,8 +54,8 @@ static DEFINE_MUTEX(markers_mutex);
struct marker_entry {
struct hlist_node hlist;
char *format;
- void (*call)(const struct marker *mdata, /* Probe wrapper */
- void *call_private, const char *fmt, ...);
+ /* Probe wrapper */
+ void (*call)(const struct marker *mdata, void *call_private, ...);
struct marker_probe_closure single;
struct marker_probe_closure *multi;
int refcount; /* Number of times armed. 0 if disarmed. */
@@ -90,15 +90,13 @@ EXPORT_SYMBOL_GPL(__mark_empty_function)
* marker_probe_cb Callback that prepares the variable argument list for probes.
* @mdata: pointer of type struct marker
* @call_private: caller site private data
- * @fmt: format string
* @...: Variable argument list.
*
* Since we do not use "typical" pointer based RCU in the 1 argument case, we
* need to put a full smp_rmb() in this branch. This is why we do not use
* rcu_dereference() for the pointer read.
*/
-void marker_probe_cb(const struct marker *mdata, void *call_private,
- const char *fmt, ...)
+void marker_probe_cb(const struct marker *mdata, void *call_private, ...)
{
va_list args;
char ptype;
@@ -119,8 +117,9 @@ void marker_probe_cb(const struct marker
/* Must read the ptr before private data. They are not data
* dependant, so we put an explicit smp_rmb() here. */
smp_rmb();
- va_start(args, fmt);
- func(mdata->single.probe_private, call_private, fmt, &args);
+ va_start(args, call_private);
+ func(mdata->single.probe_private, call_private, mdata->format,
+ &args);
va_end(args);
} else {
struct marker_probe_closure *multi;
@@ -135,9 +134,9 @@ void marker_probe_cb(const struct marker
smp_read_barrier_depends();
multi = mdata->multi;
for (i = 0; multi[i].func; i++) {
- va_start(args, fmt);
- multi[i].func(multi[i].probe_private, call_private, fmt,
- &args);
+ va_start(args, call_private);
+ multi[i].func(multi[i].probe_private, call_private,
+ mdata->format, &args);
va_end(args);
}
}
@@ -149,13 +148,11 @@ EXPORT_SYMBOL_GPL(marker_probe_cb);
* marker_probe_cb Callback that does not prepare the variable argument list.
* @mdata: pointer of type struct marker
* @call_private: caller site private data
- * @fmt: format string
* @...: Variable argument list.
*
* Should be connected to markers "MARK_NOARGS".
*/
-void marker_probe_cb_noarg(const struct marker *mdata,
- void *call_private, const char *fmt, ...)
+void marker_probe_cb_noarg(const struct marker *mdata, void *call_private, ...)
{
va_list args; /* not initialized */
char ptype;
@@ -171,7 +168,8 @@ void marker_probe_cb_noarg(const struct
/* Must read the ptr before private data. They are not data
* dependant, so we put an explicit smp_rmb() here. */
smp_rmb();
- func(mdata->single.probe_private, call_private, fmt, &args);
+ func(mdata->single.probe_private, call_private, mdata->format,
+ &args);
} else {
struct marker_probe_closure *multi;
int i;
@@ -185,8 +183,8 @@ void marker_probe_cb_noarg(const struct
smp_read_barrier_depends();
multi = mdata->multi;
for (i = 0; multi[i].func; i++)
- multi[i].func(multi[i].probe_private, call_private, fmt,
- &args);
+ multi[i].func(multi[i].probe_private, call_private,
+ mdata->format, &args);
}
preempt_enable();
}
--
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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