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Commit 1a338ac3 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

sched, x86: Optimize the preempt_schedule() call 



Remove the bloat of the C calling convention out of the
preempt_enable() sites by creating an ASM wrapper which allows us to
do an asm("call ___preempt_schedule") instead.

calling.h bits by Andi Kleen

Suggested-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: default avatarPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-tk7xdi1cvvxewixzke8t8le1@git.kernel.org


[ Fixed build error. ]
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent c2daa3be

arch/x86/include/asm/calling.h

+50 −0
Original line number Diff line number Diff line
@@ -48,6 +48,8 @@ For 32-bit we have the following conventions - kernel is built with 


#include <asm/dwarf2.h>



#ifdef CONFIG_X86_64



/*

 * 64-bit system call stack frame layout defines and helpers,

 * for assembly code:
@@ -192,3 +194,51 @@ For 32-bit we have the following conventions - kernel is built with 
	.macro icebp

	.byte 0xf1

	.endm



#else /* CONFIG_X86_64 */



/*

 * For 32bit only simplified versions of SAVE_ALL/RESTORE_ALL. These

 * are different from the entry_32.S versions in not changing the segment

 * registers. So only suitable for in kernel use, not when transitioning

 * from or to user space. The resulting stack frame is not a standard

 * pt_regs frame. The main use case is calling C code from assembler

 * when all the registers need to be preserved.

 */



	.macro SAVE_ALL

	pushl_cfi %eax

	CFI_REL_OFFSET eax, 0

	pushl_cfi %ebp

	CFI_REL_OFFSET ebp, 0

	pushl_cfi %edi

	CFI_REL_OFFSET edi, 0

	pushl_cfi %esi

	CFI_REL_OFFSET esi, 0

	pushl_cfi %edx

	CFI_REL_OFFSET edx, 0

	pushl_cfi %ecx

	CFI_REL_OFFSET ecx, 0

	pushl_cfi %ebx

	CFI_REL_OFFSET ebx, 0

	.endm



	.macro RESTORE_ALL

	popl_cfi %ebx

	CFI_RESTORE ebx

	popl_cfi %ecx

	CFI_RESTORE ecx

	popl_cfi %edx

	CFI_RESTORE edx

	popl_cfi %esi

	CFI_RESTORE esi

	popl_cfi %edi

	CFI_RESTORE edi

	popl_cfi %ebp

	CFI_RESTORE ebp

	popl_cfi %eax

	CFI_RESTORE eax

	.endm



#endif /* CONFIG_X86_64 */

arch/x86/include/asm/preempt.h

+10 −0
Original line number Diff line number Diff line
@@ -95,4 +95,14 @@ static __always_inline bool should_resched(void) 
	return unlikely(!__this_cpu_read_4(__preempt_count));

}



#ifdef CONFIG_PREEMPT

  extern asmlinkage void ___preempt_schedule(void);

# define __preempt_schedule() asm ("call ___preempt_schedule")

  extern asmlinkage void preempt_schedule(void);

# ifdef CONFIG_CONTEXT_TRACKING

    extern asmlinkage void ___preempt_schedule_context(void);

#   define __preempt_schedule_context() asm ("call ___preempt_schedule_context")

# endif

#endif



#endif /* __ASM_PREEMPT_H */

arch/x86/kernel/Makefile

+2 −0
Original line number Diff line number Diff line
@@ -36,6 +36,8 @@ obj-y += tsc.o io_delay.o rtc.o 
obj-y			+= pci-iommu_table.o

obj-y			+= resource.o



obj-$(CONFIG_PREEMPT)	+= preempt.o



obj-y				+= process.o

obj-y				+= i387.o xsave.o

obj-y				+= ptrace.o

arch/x86/kernel/i386_ksyms_32.c

+7 −0
Original line number Diff line number Diff line
@@ -37,3 +37,10 @@ EXPORT_SYMBOL(strstr); 


EXPORT_SYMBOL(csum_partial);

EXPORT_SYMBOL(empty_zero_page);



#ifdef CONFIG_PREEMPT

EXPORT_SYMBOL(___preempt_schedule);

#ifdef CONFIG_CONTEXT_TRACKING

EXPORT_SYMBOL(___preempt_schedule_context);

#endif

#endif

arch/x86/kernel/preempt.S

0 → 100644
+25 −0
Original line number Diff line number Diff line 


#include <linux/linkage.h>

#include <asm/dwarf2.h>

#include <asm/asm.h>

#include <asm/calling.h>



ENTRY(___preempt_schedule)

	CFI_STARTPROC

	SAVE_ALL

	call preempt_schedule

	RESTORE_ALL

	ret

	CFI_ENDPROC



#ifdef CONFIG_CONTEXT_TRACKING



ENTRY(___preempt_schedule_context)

	CFI_STARTPROC

	SAVE_ALL

	call preempt_schedule_context

	RESTORE_ALL

	ret

	CFI_ENDPROC



#endif