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Message-Id: <20080103165227.02fc0da4.dada1@cosmosbay.com>
Date: Thu, 3 Jan 2008 16:52:27 +0100
From: Eric Dumazet <dada1@...mosbay.com>
To: David Miller <davem@...emloft.net>
Cc: "acme@...hat.com" <acme@...hat.com>,
Herbert Xu <herbert@...dor.apana.org.au>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: [LIB] pcounter : unline too big functions
Before pushing pcounter to Linus tree, I would like to make some adjustments.
Goal is to reduce kernel text size, by unlining too big functions.
When a pcounter is bound to a statically defined per_cpu variable,
we define two small helpers functions. (No more folding function
using the fat for_each_possible_cpu(cpu) ... )
static DEFINE_PER_CPU(int, NAME##_pcounter_values);
static void NAME##_pcounter_add(struct pcounter *self, int val)
{
__get_cpu_var(NAME##_pcounter_values) += val;
}
static int NAME##_pcounter_getval(const struct pcounter *self, int cpu)
{
return per_cpu(NAME##_pcounter_values, cpu);
}
Fast path is therefore unchanged, while folding/alloc/free is now unlined.
This saves 228 bytes on i386
Signed-off-by: Eric Dumazet <dada1@...mosbay.com>
include/linux/pcounter.h | 80 ++++++++++++-------------------------
lib/pcounter.c | 42 +++++++++++++++++--
2 files changed, 63 insertions(+), 59 deletions(-)
diff --git a/include/linux/pcounter.h b/include/linux/pcounter.h
index 9c4760a..a82d9f2 100644
--- a/include/linux/pcounter.h
+++ b/include/linux/pcounter.h
@@ -1,41 +1,39 @@
#ifndef __LINUX_PCOUNTER_H
#define __LINUX_PCOUNTER_H
-
+/*
+ * Using a dynamic percpu 'int' variable has a cost :
+ * 1) Extra dereference
+ * Current per_cpu_ptr() implementation uses an array per 'percpu variable'.
+ * 2) memory cost of NR_CPUS*(32+sizeof(void *)) instead of num_possible_cpus()*4
+ *
+ * This pcounter implementation is an abstraction to be able to use
+ * either a static or a dynamic per cpu variable.
+ * One dynamic per cpu variable gets a fast & cheap implementation, we can
+ * change pcounter implementation too.
+ */
struct pcounter {
#ifdef CONFIG_SMP
void (*add)(struct pcounter *self, int inc);
- int (*getval)(const struct pcounter *self);
+ int (*getval)(const struct pcounter *self, int cpu);
int *per_cpu_values;
#else
int val;
#endif
};
-/*
- * Special macros to let pcounters use a fast version of {getvalue|add}
- * using a static percpu variable per pcounter instead of an allocated one,
- * saving one dereference.
- * This might be changed if/when dynamic percpu vars become fast.
- */
#ifdef CONFIG_SMP
-#include <linux/cpumask.h>
#include <linux/percpu.h>
-#define DEFINE_PCOUNTER(NAME) \
-static DEFINE_PER_CPU(int, NAME##_pcounter_values); \
-static void NAME##_pcounter_add(struct pcounter *self, int inc) \
-{ \
- __get_cpu_var(NAME##_pcounter_values) += inc; \
-} \
- \
-static int NAME##_pcounter_getval(const struct pcounter *self) \
-{ \
- int res = 0, cpu; \
- \
- for_each_possible_cpu(cpu) \
- res += per_cpu(NAME##_pcounter_values, cpu); \
- return res; \
-}
+#define DEFINE_PCOUNTER(NAME) \
+static DEFINE_PER_CPU(int, NAME##_pcounter_values); \
+static void NAME##_pcounter_add(struct pcounter *self, int val) \
+{ \
+ __get_cpu_var(NAME##_pcounter_values) += val; \
+} \
+static int NAME##_pcounter_getval(const struct pcounter *self, int cpu) \
+{ \
+ return per_cpu(NAME##_pcounter_values, cpu); \
+} \
#define PCOUNTER_MEMBER_INITIALIZER(NAME, MEMBER) \
MEMBER = { \
@@ -43,42 +41,16 @@ static int NAME##_pcounter_getval(const struct pcounter *self) \
.getval = NAME##_pcounter_getval, \
}
-extern void pcounter_def_add(struct pcounter *self, int inc);
-extern int pcounter_def_getval(const struct pcounter *self);
-
-static inline int pcounter_alloc(struct pcounter *self)
-{
- int rc = 0;
- if (self->add == NULL) {
- self->per_cpu_values = alloc_percpu(int);
- if (self->per_cpu_values != NULL) {
- self->add = pcounter_def_add;
- self->getval = pcounter_def_getval;
- } else
- rc = 1;
- }
- return rc;
-}
-
-static inline void pcounter_free(struct pcounter *self)
-{
- if (self->per_cpu_values != NULL) {
- free_percpu(self->per_cpu_values);
- self->per_cpu_values = NULL;
- self->getval = NULL;
- self->add = NULL;
- }
-}
static inline void pcounter_add(struct pcounter *self, int inc)
{
self->add(self, inc);
}
-static inline int pcounter_getval(const struct pcounter *self)
-{
- return self->getval(self);
-}
+extern int pcounter_getval(const struct pcounter *self);
+extern int pcounter_alloc(struct pcounter *self);
+extern void pcounter_free(struct pcounter *self);
+
#else /* CONFIG_SMP */
diff --git a/lib/pcounter.c b/lib/pcounter.c
index 93feea5..9b56807 100644
--- a/lib/pcounter.c
+++ b/lib/pcounter.c
@@ -7,20 +7,52 @@
#include <linux/module.h>
#include <linux/pcounter.h>
#include <linux/smp.h>
+#include <linux/cpumask.h>
-void pcounter_def_add(struct pcounter *self, int inc)
+static void pcounter_dyn_add(struct pcounter *self, int inc)
{
per_cpu_ptr(self->per_cpu_values, smp_processor_id())[0] += inc;
}
-EXPORT_SYMBOL_GPL(pcounter_def_add);
+static int pcounter_dyn_getval(const struct pcounter *self, int cpu)
+{
+ return per_cpu_ptr(self->per_cpu_values, cpu)[0];
+}
-int pcounter_def_getval(const struct pcounter *self)
+int pcounter_getval(const struct pcounter *self)
{
int res = 0, cpu;
+
for_each_possible_cpu(cpu)
- res += per_cpu_ptr(self->per_cpu_values, cpu)[0];
+ res += self->getval(self, cpu);
+
return res;
}
+EXPORT_SYMBOL_GPL(pcounter_getval);
+
+int pcounter_alloc(struct pcounter *self)
+{
+ int rc = 0;
+ if (self->add == NULL) {
+ self->per_cpu_values = alloc_percpu(int);
+ if (self->per_cpu_values != NULL) {
+ self->add = pcounter_dyn_add;
+ self->getval = pcounter_dyn_getval;
+ } else
+ rc = 1;
+ }
+ return rc;
+}
+EXPORT_SYMBOL_GPL(pcounter_alloc);
+
+void pcounter_free(struct pcounter *self)
+{
+ if (self->per_cpu_values != NULL) {
+ free_percpu(self->per_cpu_values);
+ self->per_cpu_values = NULL;
+ self->getval = NULL;
+ self->add = NULL;
+ }
+}
+EXPORT_SYMBOL_GPL(pcounter_free);
-EXPORT_SYMBOL_GPL(pcounter_def_getval);
--
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