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>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 14 insertions, 16 deletions

diff --git a/kernel/marker.c b/kernel/marker.c
index b5a9fe1d50d5..1abfb923b761 100644
--- a/kernel/marker.c
+++ b/kernel/marker.c
@@ -55,8 +55,8 @@ 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. */
@@ -91,15 +91,13 @@ 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;
@@ -120,8 +118,9 @@ void marker_probe_cb(const struct marker *mdata, void *call_private,
                 /* 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;
@@ -136,9 +135,9 @@ void marker_probe_cb(const struct marker *mdata, void *call_private,
                 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);
                 }
         }
@@ -150,13 +149,11 @@ 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;
@@ -172,7 +169,8 @@ void marker_probe_cb_noarg(const struct marker *mdata,
                 /* 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;
@@ -186,8 +184,8 @@ void marker_probe_cb_noarg(const struct marker *mdata,
                 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();
 }