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Date: Thu, 8 Oct 2009 13:57:53 -0400 (EDT)
From: Christoph Lameter <cl@...ux-foundation.org>
To: Rusty Russell <rusty@...tcorp.com.au>
cc: Ingo Molnar <mingo@...e.hu>, akpm@...ux-foundation.org,
linux-kernel@...r.kernel.org, David Howells <dhowells@...hat.com>,
Tejun Heo <tj@...nel.org>, Eric Dumazet <dada1@...mosbay.com>,
Pekka Enberg <penberg@...helsinki.fi>
Subject: [Patchs vs. percpu-next] Use this_cpu_xx to dynamically allocate
counters
On Tue, 6 Oct 2009, Rusty Russell wrote:
> Does this mean we can kill local.h soon?
Can we remove local.h from modules?
Subject: Module handling: Use this_cpu_xx to dynamically allocate counters
Use cpu ops to deal with the per cpu data instead of a local_t. Reduces memory
requirements, cache footprint and decreases cycle counts.
The this_cpu_xx operations are also used for !SMP mode. Otherwise we could
not drop the use of __module_ref_addr() which would make per cpu data handling
complicated. this_cpu_xx operations have their own fallback for !SMP.
Signed-off-by: Christoph Lameter <cl@...ux-foundation.org>
---
include/linux/module.h | 36 ++++++++++++------------------------
kernel/module.c | 30 ++++++++++++++++--------------
kernel/trace/ring_buffer.c | 1 +
3 files changed, 29 insertions(+), 38 deletions(-)
Index: linux-2.6/include/linux/module.h
===================================================================
--- linux-2.6.orig/include/linux/module.h 2009-10-08 11:36:05.000000000 -0500
+++ linux-2.6/include/linux/module.h 2009-10-08 11:40:57.000000000 -0500
@@ -16,8 +16,7 @@
#include <linux/kobject.h>
#include <linux/moduleparam.h>
#include <linux/tracepoint.h>
-
-#include <asm/local.h>
+#include <linux/percpu.h>
#include <asm/module.h>
#include <trace/events/module.h>
@@ -361,11 +360,9 @@ struct module
/* Destruction function. */
void (*exit)(void);
-#ifdef CONFIG_SMP
- char *refptr;
-#else
- local_t ref;
-#endif
+ struct module_ref {
+ int count;
+ } *refptr;
#endif
#ifdef CONFIG_CONSTRUCTORS
@@ -452,25 +449,16 @@ void __symbol_put(const char *symbol);
#define symbol_put(x) __symbol_put(MODULE_SYMBOL_PREFIX #x)
void symbol_put_addr(void *addr);
-static inline local_t *__module_ref_addr(struct module *mod, int cpu)
-{
-#ifdef CONFIG_SMP
- return (local_t *) (mod->refptr + per_cpu_offset(cpu));
-#else
- return &mod->ref;
-#endif
-}
-
/* Sometimes we know we already have a refcount, and it's easier not
to handle the error case (which only happens with rmmod --wait). */
static inline void __module_get(struct module *module)
{
if (module) {
- unsigned int cpu = get_cpu();
- local_inc(__module_ref_addr(module, cpu));
+ preempt_disable();
+ __this_cpu_inc(module->refptr->count);
trace_module_get(module, _THIS_IP_,
- local_read(__module_ref_addr(module, cpu)));
- put_cpu();
+ __this_cpu_read(module->refptr->count));
+ preempt_enable();
}
}
@@ -479,15 +467,15 @@ static inline int try_module_get(struct
int ret = 1;
if (module) {
- unsigned int cpu = get_cpu();
if (likely(module_is_live(module))) {
- local_inc(__module_ref_addr(module, cpu));
+ preempt_disable();
+ __this_cpu_inc(module->refptr->count);
trace_module_get(module, _THIS_IP_,
- local_read(__module_ref_addr(module, cpu)));
+ __this_cpu_read(module->refptr->count));
+ preempt_enable();
}
else
ret = 0;
- put_cpu();
}
return ret;
}
Index: linux-2.6/kernel/module.c
===================================================================
--- linux-2.6.orig/kernel/module.c 2009-10-08 11:36:05.000000000 -0500
+++ linux-2.6/kernel/module.c 2009-10-08 11:42:05.000000000 -0500
@@ -474,9 +474,10 @@ static void module_unload_init(struct mo
INIT_LIST_HEAD(&mod->modules_which_use_me);
for_each_possible_cpu(cpu)
- local_set(__module_ref_addr(mod, cpu), 0);
+ per_cpu_ptr(mod->refptr, cpu)->count = 0;
+
/* Hold reference count during initialization. */
- local_set(__module_ref_addr(mod, raw_smp_processor_id()), 1);
+ __this_cpu_write(mod->refptr->count, 1);
/* Backwards compatibility macros put refcount during init. */
mod->waiter = current;
}
@@ -555,6 +556,7 @@ static void module_unload_free(struct mo
kfree(use);
sysfs_remove_link(i->holders_dir, mod->name);
/* There can be at most one match. */
+ free_percpu(i->refptr);
break;
}
}
@@ -619,7 +621,7 @@ unsigned int module_refcount(struct modu
int cpu;
for_each_possible_cpu(cpu)
- total += local_read(__module_ref_addr(mod, cpu));
+ total += per_cpu_ptr(mod->refptr, cpu)->count;
return total;
}
EXPORT_SYMBOL(module_refcount);
@@ -796,14 +798,15 @@ static struct module_attribute refcnt =
void module_put(struct module *module)
{
if (module) {
- unsigned int cpu = get_cpu();
- local_dec(__module_ref_addr(module, cpu));
+ preempt_disable();
+ __this_cpu_dec(module->refptr->count);
+
trace_module_put(module, _RET_IP_,
- local_read(__module_ref_addr(module, cpu)));
+ __this_cpu_read(module->refptr->count));
/* Maybe they're waiting for us to drop reference? */
if (unlikely(!module_is_live(module)))
wake_up_process(module->waiter);
- put_cpu();
+ preempt_enable();
}
}
EXPORT_SYMBOL(module_put);
@@ -1377,9 +1380,9 @@ static void free_module(struct module *m
kfree(mod->args);
if (mod->percpu)
percpu_modfree(mod->percpu);
-#if defined(CONFIG_MODULE_UNLOAD) && defined(CONFIG_SMP)
+#if defined(CONFIG_MODULE_UNLOAD)
if (mod->refptr)
- percpu_modfree(mod->refptr);
+ free_percpu(mod->refptr);
#endif
/* Free lock-classes: */
lockdep_free_key_range(mod->module_core, mod->core_size);
@@ -2145,9 +2148,8 @@ static noinline struct module *load_modu
mod = (void *)sechdrs[modindex].sh_addr;
kmemleak_load_module(mod, hdr, sechdrs, secstrings);
-#if defined(CONFIG_MODULE_UNLOAD) && defined(CONFIG_SMP)
- mod->refptr = percpu_modalloc(sizeof(local_t), __alignof__(local_t),
- mod->name);
+#if defined(CONFIG_MODULE_UNLOAD)
+ mod->refptr = alloc_percpu(struct module_ref);
if (!mod->refptr) {
err = -ENOMEM;
goto free_init;
@@ -2373,8 +2375,8 @@ static noinline struct module *load_modu
kobject_put(&mod->mkobj.kobj);
free_unload:
module_unload_free(mod);
-#if defined(CONFIG_MODULE_UNLOAD) && defined(CONFIG_SMP)
- percpu_modfree(mod->refptr);
+#if defined(CONFIG_MODULE_UNLOAD)
+ free_percpu(mod->refptr);
free_init:
#endif
module_free(mod, mod->module_init);
Index: linux-2.6/kernel/trace/ring_buffer.c
===================================================================
--- linux-2.6.orig/kernel/trace/ring_buffer.c 2009-10-08 12:46:29.000000000 -0500
+++ linux-2.6/kernel/trace/ring_buffer.c 2009-10-08 12:46:46.000000000 -0500
@@ -12,6 +12,7 @@
#include <linux/hardirq.h>
#include <linux/kmemcheck.h>
#include <linux/module.h>
+#include <asm/local.h>
#include <linux/percpu.h>
#include <linux/mutex.h>
#include <linux/init.h>
--
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