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rcu: Remove TINY_RCU bloat from pointless boot parameters 

The rcu_expedited, rcu_normal, and rcu_normal_after_boot kernel boot
parameters are pointless in the case of TINY_RCU because in that case
synchronous grace periods, both expedited and normal, are no-ops.
However, these three symbols contribute several hundred bytes of bloat.
This commit therefore uses CPP directives to avoid compiling this code
in TINY_RCU kernels.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
This commit is contained in:
Paul E. McKenney 2015-12-07 13:09:52 -08:00
parent 3e42ec1aa7
commit 79cfea0273
4 changed files with 24 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

13
Documentation/kernel-parameters.txt
View File

@ -3308,20 +3308,23 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
of synchronize_rcu(). This reduces latency,
but can increase CPU utilization, degrade
real-time latency, and degrade energy efficiency.
No effect on CONFIG_TINY_RCU kernels.
rcupdate.rcu_normal= [KNL]
Use only normal grace-period primitives,
for example, synchronize_rcu() instead of
synchronize_rcu_expedited(). This improves
real-time latency, CPU utilization, and energy
efficiency, but can expose users to increased
grace-period latency. This parameter overrides
rcupdate.rcu_expedited.
real-time latency, CPU utilization, and
energy efficiency, but can expose users to
increased grace-period latency. This parameter
overrides rcupdate.rcu_expedited. No effect on
CONFIG_TINY_RCU kernels.
rcupdate.rcu_normal_after_boot= [KNL]
Once boot has completed (that is, after
rcu_end_inkernel_boot() has been invoked), use
only normal grace-period primitives.
only normal grace-period primitives. No effect
on CONFIG_TINY_RCU kernels.
rcupdate.rcu_task_stall_timeout= [KNL]
Set timeout in jiffies for RCU task stall warning

9
include/linux/rcupdate.h
View File

@ -48,8 +48,10 @@
#include <asm/barrier.h>
#ifndef CONFIG_TINY_RCU
extern int rcu_expedited; /* for sysctl */
extern int rcu_normal; /* also for sysctl */
#endif /* #ifndef CONFIG_TINY_RCU */
#ifdef CONFIG_TINY_RCU
/* Tiny RCU doesn't expedite, as its purpose in life is instead to be tiny. */
@ -327,7 +329,6 @@ static inline int rcu_preempt_depth(void)
/* Internal to kernel */
void rcu_init(void);
void rcu_end_inkernel_boot(void);
void rcu_sched_qs(void);
void rcu_bh_qs(void);
void rcu_check_callbacks(int user);
@ -335,6 +336,12 @@ struct notifier_block;
int rcu_cpu_notify(struct notifier_block *self,
unsigned long action, void *hcpu);
#ifndef CONFIG_TINY_RCU
void rcu_end_inkernel_boot(void);
#else /* #ifndef CONFIG_TINY_RCU */
static inline void rcu_end_inkernel_boot(void) { }
#endif /* #ifndef CONFIG_TINY_RCU */
#ifdef CONFIG_RCU_STALL_COMMON
void rcu_sysrq_start(void);
void rcu_sysrq_end(void);

4
kernel/ksysfs.c
View File

@ -144,6 +144,7 @@ static ssize_t fscaps_show(struct kobject *kobj,
}
KERNEL_ATTR_RO(fscaps);
#ifndef CONFIG_TINY_RCU
int rcu_expedited;
static ssize_t rcu_expedited_show(struct kobject *kobj,
struct kobj_attribute *attr, char *buf)
@ -177,6 +178,7 @@ static ssize_t rcu_normal_store(struct kobject *kobj,
return count;
}
KERNEL_ATTR_RW(rcu_normal);
#endif /* #ifndef CONFIG_TINY_RCU */
/*
* Make /sys/kernel/notes give the raw contents of our kernel .notes section.
@ -219,8 +221,10 @@ static struct attribute * kernel_attrs[] = {
&kexec_crash_size_attr.attr,
&vmcoreinfo_attr.attr,
#endif
#ifndef CONFIG_TINY_RCU
&rcu_expedited_attr.attr,
&rcu_normal_attr.attr,
#endif
NULL
};

7
kernel/rcu/update.c
View File

@ -60,11 +60,12 @@ MODULE_ALIAS("rcupdate");
#endif
#define MODULE_PARAM_PREFIX "rcupdate."
#ifndef CONFIG_TINY_RCU
module_param(rcu_expedited, int, 0);
module_param(rcu_normal, int, 0);
static int rcu_normal_after_boot;
module_param(rcu_normal_after_boot, int, 0);
#endif /* #ifndef CONFIG_TINY_RCU */
#if defined(CONFIG_DEBUG_LOCK_ALLOC) && defined(CONFIG_PREEMPT_COUNT)
/**
@ -172,8 +173,6 @@ void rcu_unexpedite_gp(void)
}
EXPORT_SYMBOL_GPL(rcu_unexpedite_gp);
#endif /* #ifndef CONFIG_TINY_RCU */
/*
* Inform RCU of the end of the in-kernel boot sequence.
*/
@ -185,6 +184,8 @@ void rcu_end_inkernel_boot(void)
WRITE_ONCE(rcu_normal, 1);
}
#endif /* #ifndef CONFIG_TINY_RCU */
#ifdef CONFIG_PREEMPT_RCU
/*