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Commit 79cfea02 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

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: default avatarkbuild test robot <fengguang.wu@intel.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: default avatarJosh Triplett <josh@joshtriplett.org>
parent 3e42ec1a

Documentation/kernel-parameters.txt

+8 −5
Original line number Diff line number Diff line
@@ -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

include/linux/rcupdate.h

+8 −1
Original line number Diff line number Diff line
@@ -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);

kernel/ksysfs.c

+4 −0
Original line number Diff line number Diff line
@@ -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

};

kernel/rcu/update.c

+4 −3
Original line number Diff line number Diff line
@@ -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



/*