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Message-ID: <nycvar.YSQ.7.76.1710021347550.5407@knanqh.ubzr>
Date: Mon, 2 Oct 2017 13:59:13 -0400 (EDT)
From: Nicolas Pitre <nicolas.pitre@...aro.org>
To: Thomas Gleixner <tglx@...utronix.de>
cc: linux-kernel@...r.kernel.org
Subject: [PATCH/RFC] cpuhp code and data usage on UP systems
On !SMP systems, we end up with the following array definition:
static struct cpuhp_step cpuhp_ap_states[] = {
[CPUHP_ONLINE] = {
.name = "online",
.startup.single = NULL,
.teardown.single = NULL,
},
};
where CPUHP_ONLINE = 187. That means up to 99.5% of this array is unused
but still allocated in the kernel's .data section i.e. 3760 bytes.
The same issue exists with cpuhp_bp_states being 1720 bytes.
The goal of this patch is mainly about illustrating the issue and
reducing .data usage. I have no clear idea when this stuff is really
needed besides standard CPU hotplug. Not knowing exactly what I'm doing
here, I made it conditional on CONFIG_SMP for now. There might be a case
for moving that code to a separate file (cpuhp.c maybe?) and omitting it
from the kernel when unneeded.
Comments?
include/linux/cpu.h | 4 ++++
include/linux/cpuhotplug.h | 27 +++++++++++++++++++--------
kernel/cpu.c | 26 ++++++++++++++++----------
kernel/power/Kconfig | 3 +++
4 files changed, 42 insertions(+), 18 deletions(-)
diff --git a/kernel/cpu.c b/kernel/cpu.c
index acf5308fad..46756fb980 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -35,6 +35,8 @@
#include "smpboot.h"
+#ifdef CONFIG_CPUHP
+
/**
* cpuhp_cpu_state - Per cpu hotplug state storage
* @state: The current cpu state
@@ -1036,8 +1038,6 @@ core_initcall(cpu_hotplug_pm_sync_init);
#endif /* CONFIG_PM_SLEEP_SMP */
-int __boot_cpu_id;
-
#endif /* CONFIG_SMP */
/* Boot processor state steps */
@@ -1709,6 +1709,16 @@ device_initcall(cpuhp_sysfs_init);
#endif
/*
+ * Must be called _AFTER_ setting up the per_cpu areas
+ */
+void __init boot_cpu_state_init(void)
+{
+ per_cpu_ptr(&cpuhp_state, smp_processor_id())->state = CPUHP_ONLINE;
+}
+
+#endif /* CONFIG_CPUHP */
+
+/*
* cpu_bit_bitmap[] is a special, "compressed" data structure that
* represents all NR_CPUS bits binary values of 1<<nr.
*
@@ -1768,6 +1778,10 @@ void init_cpu_online(const struct cpumask *src)
cpumask_copy(&__cpu_online_mask, src);
}
+#ifdef CONFIG_SMP
+int __boot_cpu_id;
+#endif
+
/*
* Activate the first processor.
*/
@@ -1785,11 +1799,3 @@ void __init boot_cpu_init(void)
__boot_cpu_id = cpu;
#endif
}
-
-/*
- * Must be called _AFTER_ setting up the per_cpu areas
- */
-void __init boot_cpu_state_init(void)
-{
- per_cpu_ptr(&cpuhp_state, smp_processor_id())->state = CPUHP_ONLINE;
-}
diff --git a/include/linux/cpu.h b/include/linux/cpu.h
index ca73bc1563..4130ede0f9 100644
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -29,7 +29,11 @@ struct cpu {
};
extern void boot_cpu_init(void);
+#ifdef CONFIG_CPUHP
extern void boot_cpu_state_init(void);
+#else
+static inline void boot_cpu_state_init(void) { }
+#endif
extern void cpu_init(void);
extern void trap_init(void);
diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
index f24bfb2b9a..c51e2980a7 100644
--- a/include/linux/cpuhotplug.h
+++ b/include/linux/cpuhotplug.h
@@ -150,15 +150,23 @@ enum cpuhp_state {
CPUHP_ONLINE,
};
+#ifdef CONFIG_CPUHP
+#define ___P(proto, def_retcode) extern proto;
+#else
+#define ___P(proto, def_retcode) static inline proto { return def_retcode }
+#endif
+
+___P(
int __cpuhp_setup_state(enum cpuhp_state state, const char *name, bool invoke,
int (*startup)(unsigned int cpu),
- int (*teardown)(unsigned int cpu), bool multi_instance);
-
+ int (*teardown)(unsigned int cpu), bool multi_instance), 0; )
+___P(
int __cpuhp_setup_state_cpuslocked(enum cpuhp_state state, const char *name,
bool invoke,
int (*startup)(unsigned int cpu),
int (*teardown)(unsigned int cpu),
- bool multi_instance);
+ bool multi_instance), 0; )
+
/**
* cpuhp_setup_state - Setup hotplug state callbacks with calling the callbacks
* @state: The state for which the calls are installed
@@ -239,10 +247,12 @@ static inline int cpuhp_setup_state_multi(enum cpuhp_state state,
(void *) teardown, true);
}
+___P(
int __cpuhp_state_add_instance(enum cpuhp_state state, struct hlist_node *node,
- bool invoke);
+ bool invoke), 0; )
+___P(
int __cpuhp_state_add_instance_cpuslocked(enum cpuhp_state state,
- struct hlist_node *node, bool invoke);
+ struct hlist_node *node, bool invoke), 0; )
/**
* cpuhp_state_add_instance - Add an instance for a state and invoke startup
@@ -282,8 +292,8 @@ cpuhp_state_add_instance_nocalls_cpuslocked(enum cpuhp_state state,
return __cpuhp_state_add_instance_cpuslocked(state, node, false);
}
-void __cpuhp_remove_state(enum cpuhp_state state, bool invoke);
-void __cpuhp_remove_state_cpuslocked(enum cpuhp_state state, bool invoke);
+___P( void __cpuhp_remove_state(enum cpuhp_state state, bool invoke), ; )
+___P( void __cpuhp_remove_state_cpuslocked(enum cpuhp_state state, bool invoke), ; )
/**
* cpuhp_remove_state - Remove hotplug state callbacks and invoke the teardown
@@ -325,8 +335,9 @@ static inline void cpuhp_remove_multi_state(enum cpuhp_state state)
__cpuhp_remove_state(state, false);
}
+___P(
int __cpuhp_state_remove_instance(enum cpuhp_state state,
- struct hlist_node *node, bool invoke);
+ struct hlist_node *node, bool invoke), 0; )
/**
* cpuhp_state_remove_instance - Remove hotplug instance from state and invoke
diff --git a/kernel/power/Kconfig b/kernel/power/Kconfig
index e8517b63eb..28acf47105 100644
--- a/kernel/power/Kconfig
+++ b/kernel/power/Kconfig
@@ -311,3 +311,6 @@ config PM_GENERIC_DOMAINS_OF
config CPU_PM
bool
+
+config CPUHP
+ def_bool SMP
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