Commit c360192b authored by Martin Schwidefsky's avatar Martin Schwidefsky
Browse files

s390/preempt: move preempt_count to the lowcore 



Convert s390 to use a field in the struct lowcore for the CPU
preemption count. It is a bit cheaper to access a lowcore field
compared to a thread_info variable and it removes the depencency
on a task related structure.

bloat-o-meter on the vmlinux image for the default configuration
(CONFIG_PREEMPT_NONE=y) reports a small reduction in text size:

add/remove: 0/0 grow/shrink: 18/578 up/down: 228/-5448 (-5220)

A larger improvement is achieved with the default configuration
but with CONFIG_PREEMPT=y and CONFIG_DEBUG_PREEMPT=n:

add/remove: 2/6 grow/shrink: 59/4477 up/down: 1618/-228762 (-227144)

Reviewed-by: default avatarHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
parent 1993dbc7

arch/s390/include/asm/lowcore.h

+2 −1
Original line number Diff line number Diff line
@@ -126,7 +126,8 @@ struct lowcore { 
	__u64	percpu_offset;			/* 0x0378 */

	__u64	vdso_per_cpu_data;		/* 0x0380 */

	__u64	machine_flags;			/* 0x0388 */

	__u8	pad_0x0390[0x0398-0x0390];	/* 0x0390 */

	__u32	preempt_count;			/* 0x0390 */

	__u8	pad_0x0394[0x0398-0x0394];	/* 0x0394 */

	__u64	gmap;				/* 0x0398 */

	__u32	spinlock_lockval;		/* 0x03a0 */

	__u32	fpu_flags;			/* 0x03a4 */

arch/s390/include/asm/preempt.h

0 → 100644
+137 −0
Original line number Diff line number Diff line 
#ifndef __ASM_PREEMPT_H

#define __ASM_PREEMPT_H



#include <asm/current.h>

#include <linux/thread_info.h>

#include <asm/atomic_ops.h>



#ifdef CONFIG_HAVE_MARCH_Z196_FEATURES



#define PREEMPT_ENABLED	(0 + PREEMPT_NEED_RESCHED)



static inline int preempt_count(void)

{

	return READ_ONCE(S390_lowcore.preempt_count) & ~PREEMPT_NEED_RESCHED;

}



static inline void preempt_count_set(int pc)

{

	int old, new;



	do {

		old = READ_ONCE(S390_lowcore.preempt_count);

		new = (old & PREEMPT_NEED_RESCHED) |

			(pc & ~PREEMPT_NEED_RESCHED);

	} while (__atomic_cmpxchg(&S390_lowcore.preempt_count,

				  old, new) != old);

}



#define init_task_preempt_count(p)	do { } while (0)



#define init_idle_preempt_count(p, cpu)	do { \

	S390_lowcore.preempt_count = PREEMPT_ENABLED; \

} while (0)



static inline void set_preempt_need_resched(void)

{

	__atomic_and(~PREEMPT_NEED_RESCHED, &S390_lowcore.preempt_count);

}



static inline void clear_preempt_need_resched(void)

{

	__atomic_or(PREEMPT_NEED_RESCHED, &S390_lowcore.preempt_count);

}



static inline bool test_preempt_need_resched(void)

{

	return !(READ_ONCE(S390_lowcore.preempt_count) & PREEMPT_NEED_RESCHED);

}



static inline void __preempt_count_add(int val)

{

	if (__builtin_constant_p(val) && (val >= -128) && (val <= 127))

		__atomic_add_const(val, &S390_lowcore.preempt_count);

	else

		__atomic_add(val, &S390_lowcore.preempt_count);

}



static inline void __preempt_count_sub(int val)

{

	__preempt_count_add(-val);

}



static inline bool __preempt_count_dec_and_test(void)

{

	return __atomic_add(-1, &S390_lowcore.preempt_count) == 1;

}



static inline bool should_resched(int preempt_offset)

{

	return unlikely(READ_ONCE(S390_lowcore.preempt_count) ==

			preempt_offset);

}



#else /* CONFIG_HAVE_MARCH_Z196_FEATURES */



#define PREEMPT_ENABLED	(0)



static inline int preempt_count(void)

{

	return READ_ONCE(S390_lowcore.preempt_count);

}



static inline void preempt_count_set(int pc)

{

	S390_lowcore.preempt_count = pc;

}



#define init_task_preempt_count(p)	do { } while (0)



#define init_idle_preempt_count(p, cpu)	do { \

	S390_lowcore.preempt_count = PREEMPT_ENABLED; \

} while (0)



static inline void set_preempt_need_resched(void)

{

}



static inline void clear_preempt_need_resched(void)

{

}



static inline bool test_preempt_need_resched(void)

{

	return false;

}



static inline void __preempt_count_add(int val)

{

	S390_lowcore.preempt_count += val;

}



static inline void __preempt_count_sub(int val)

{

	S390_lowcore.preempt_count -= val;

}



static inline bool __preempt_count_dec_and_test(void)

{

	return !--S390_lowcore.preempt_count && tif_need_resched();

}



static inline bool should_resched(int preempt_offset)

{

	return unlikely(preempt_count() == preempt_offset &&

			tif_need_resched());

}



#endif /* CONFIG_HAVE_MARCH_Z196_FEATURES */



#ifdef CONFIG_PREEMPT

extern asmlinkage void preempt_schedule(void);

#define __preempt_schedule() preempt_schedule()

extern asmlinkage void preempt_schedule_notrace(void);

#define __preempt_schedule_notrace() preempt_schedule_notrace()

#endif /* CONFIG_PREEMPT */



#endif /* __ASM_PREEMPT_H */

arch/s390/include/asm/thread_info.h

+0 −2
Original line number Diff line number Diff line
@@ -34,7 +34,6 @@ struct thread_info { 
	unsigned long		flags;		/* low level flags */

	unsigned long		sys_call_table;	/* System call table address */

	unsigned int		cpu;		/* current CPU */

	int			preempt_count;	/* 0 => preemptable, <0 => BUG */

	unsigned int		system_call;

	__u64			user_timer;

	__u64			system_timer;
@@ -49,7 +48,6 @@ struct thread_info { 
	.task		= &tsk,			\

	.flags		= 0,			\

	.cpu		= 0,			\

	.preempt_count	= INIT_PREEMPT_COUNT,	\

}



#define init_thread_info	(init_thread_union.thread_info)

arch/s390/kernel/asm-offsets.c

+1 −1
Original line number Diff line number Diff line
@@ -43,7 +43,6 @@ int main(void) 
	OFFSET(__TI_flags, thread_info, flags);

	OFFSET(__TI_sysc_table, thread_info, sys_call_table);

	OFFSET(__TI_cpu, thread_info, cpu);

	OFFSET(__TI_precount, thread_info, preempt_count);

	OFFSET(__TI_user_timer, thread_info, user_timer);

	OFFSET(__TI_system_timer, thread_info, system_timer);

	OFFSET(__TI_last_break, thread_info, last_break);
@@ -175,6 +174,7 @@ int main(void) 
	OFFSET(__LC_PERCPU_OFFSET, lowcore, percpu_offset);

	OFFSET(__LC_VDSO_PER_CPU, lowcore, vdso_per_cpu_data);

	OFFSET(__LC_MACHINE_FLAGS, lowcore, machine_flags);

	OFFSET(__LC_PREEMPT_COUNT, lowcore, preempt_count);

	OFFSET(__LC_GMAP, lowcore, gmap);

	OFFSET(__LC_PASTE, lowcore, paste);

	/* software defined ABI-relevant lowcore locations 0xe00 - 0xe20 */

arch/s390/kernel/early.c

+1 −0
Original line number Diff line number Diff line
@@ -293,6 +293,7 @@ static noinline __init void setup_lowcore_early(void) 
	psw.addr = (unsigned long) s390_base_pgm_handler;

	S390_lowcore.program_new_psw = psw;

	s390_base_pgm_handler_fn = early_pgm_check_handler;

	S390_lowcore.preempt_count = INIT_PREEMPT_COUNT;

}



static noinline __init void setup_facility_list(void)

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