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Commit 909ea964 authored by Christoph Lameter's avatar Christoph Lameter Committed by Tejun Heo
Browse files

core: Replace __get_cpu_var with __this_cpu_read if not used for an address. 



__get_cpu_var() can be replaced with this_cpu_read and will then use a
single read instruction with implied address calculation to access the
correct per cpu instance.

However, the address of a per cpu variable passed to __this_cpu_read()
cannot be determined (since it's an implied address conversion through
segment prefixes).  Therefore apply this only to uses of __get_cpu_var
where the address of the variable is not used.

Cc: Pekka Enberg <penberg@cs.helsinki.fi>
Cc: Hugh Dickins <hughd@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Acked-by: default avatarH. Peter Anvin <hpa@zytor.com>
Signed-off-by: default avatarChristoph Lameter <cl@linux.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent 780f36d8

include/asm-generic/irq_regs.h

+4 −4
Original line number Diff line number Diff line
@@ -22,15 +22,15 @@ DECLARE_PER_CPU(struct pt_regs *, __irq_regs); 


static inline struct pt_regs *get_irq_regs(void)

{

	return __get_cpu_var(__irq_regs);

	return __this_cpu_read(__irq_regs);

}



static inline struct pt_regs *set_irq_regs(struct pt_regs *new_regs)

{

	struct pt_regs *old_regs, **pp_regs = &__get_cpu_var(__irq_regs);

	struct pt_regs *old_regs;



	old_regs = *pp_regs;

	*pp_regs = new_regs;

	old_regs = __this_cpu_read(__irq_regs);

	__this_cpu_write(__irq_regs, new_regs);

	return old_regs;

}

include/linux/elevator.h

+3 −9
Original line number Diff line number Diff line
@@ -195,15 +195,9 @@ enum { 
/*

 * io context count accounting

 */

#define elv_ioc_count_mod(name, __val)				\

	do {							\

		preempt_disable();				\

		__get_cpu_var(name) += (__val);			\

		preempt_enable();				\

	} while (0)



#define elv_ioc_count_inc(name)	elv_ioc_count_mod(name, 1)

#define elv_ioc_count_dec(name)	elv_ioc_count_mod(name, -1)

#define elv_ioc_count_mod(name, __val) this_cpu_add(name, __val)

#define elv_ioc_count_inc(name)	this_cpu_inc(name)

#define elv_ioc_count_dec(name)	this_cpu_dec(name)



#define elv_ioc_count_read(name)				\

({								\

include/linux/kernel_stat.h

+1 −1
Original line number Diff line number Diff line
@@ -47,7 +47,7 @@ extern unsigned long long nr_context_switches(void); 


#ifndef CONFIG_GENERIC_HARDIRQS

#define kstat_irqs_this_cpu(irq) \

	(kstat_this_cpu.irqs[irq])

	(this_cpu_read(kstat.irqs[irq])



struct irq_desc;

kernel/exit.c

+1 −1
Original line number Diff line number Diff line
@@ -69,7 +69,7 @@ static void __unhash_process(struct task_struct *p, bool group_dead) 


		list_del_rcu(&p->tasks);

		list_del_init(&p->sibling);

		__get_cpu_var(process_counts)--;

		__this_cpu_dec(process_counts);

	}

	list_del_rcu(&p->thread_group);

}

kernel/fork.c

+1 −1
Original line number Diff line number Diff line
@@ -1282,7 +1282,7 @@ static struct task_struct *copy_process(unsigned long clone_flags, 
			attach_pid(p, PIDTYPE_SID, task_session(current));

			list_add_tail(&p->sibling, &p->real_parent->children);

			list_add_tail_rcu(&p->tasks, &init_task.tasks);

			__get_cpu_var(process_counts)++;

			__this_cpu_inc(process_counts);

		}

		attach_pid(p, PIDTYPE_PID, pid);

		nr_threads++;