79ab11cdb9
For spinning loops people do often use barrier() or cpu_relax(). For most architectures cpu_relax and barrier are the same, but on some architectures cpu_relax can add some latency. For example on power,sparc64 and arc, cpu_relax can shift the CPU towards other hardware threads in an SMT environment. On s390 cpu_relax does even more, it uses an hypercall to the hypervisor to give up the timeslice. In contrast to the SMT yielding this can result in larger latencies. In some places this latency is unwanted, so another variant "cpu_relax_lowlatency" was introduced. Before this is used in more and more places, lets revert the logic and provide a cpu_relax_yield that can be called in places where yielding is more important than latency. By default this is the same as cpu_relax on all architectures. Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Nicholas Piggin <npiggin@gmail.com> Cc: Noam Camus <noamc@ezchip.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Russell King <linux@armlinux.org.uk> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Will Deacon <will.deacon@arm.com> Cc: linuxppc-dev@lists.ozlabs.org Cc: virtualization@lists.linux-foundation.org Cc: xen-devel@lists.xenproject.org Link: http://lkml.kernel.org/r/1477386195-32736-2-git-send-email-borntraeger@de.ibm.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
139 lines
3.3 KiB
C
139 lines
3.3 KiB
C
/*
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* include/asm-h8300/processor.h
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*
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* Copyright (C) 2002 Yoshinori Sato
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*
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* Based on: linux/asm-m68nommu/processor.h
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*
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* Copyright (C) 1995 Hamish Macdonald
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*/
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#ifndef __ASM_H8300_PROCESSOR_H
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#define __ASM_H8300_PROCESSOR_H
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/*
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* Default implementation of macro that returns current
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* instruction pointer ("program counter").
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*/
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#define current_text_addr() ({ __label__ _l; _l: &&_l; })
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#include <linux/compiler.h>
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#include <asm/segment.h>
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#include <asm/ptrace.h>
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#include <asm/current.h>
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static inline unsigned long rdusp(void)
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{
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extern unsigned int _sw_usp;
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return _sw_usp;
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}
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static inline void wrusp(unsigned long usp)
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{
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extern unsigned int _sw_usp;
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_sw_usp = usp;
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}
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/*
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* User space process size: 3.75GB. This is hardcoded into a few places,
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* so don't change it unless you know what you are doing.
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*/
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#define TASK_SIZE (0xFFFFFFFFUL)
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#ifdef __KERNEL__
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#define STACK_TOP TASK_SIZE
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#define STACK_TOP_MAX STACK_TOP
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#endif
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/*
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* This decides where the kernel will search for a free chunk of vm
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* space during mmap's. We won't be using it
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*/
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#define TASK_UNMAPPED_BASE 0
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struct thread_struct {
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unsigned long ksp; /* kernel stack pointer */
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unsigned long usp; /* user stack pointer */
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unsigned long ccr; /* saved status register */
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unsigned long esp0; /* points to SR of stack frame */
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struct {
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unsigned short *addr;
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unsigned short inst;
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} breakinfo;
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};
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#define INIT_THREAD { \
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.ksp = sizeof(init_stack) + (unsigned long)init_stack, \
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.usp = 0, \
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.ccr = PS_S, \
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.esp0 = 0, \
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.breakinfo = { \
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.addr = (unsigned short *)-1, \
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.inst = 0 \
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} \
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}
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/*
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* Do necessary setup to start up a newly executed thread.
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*
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* pass the data segment into user programs if it exists,
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* it can't hurt anything as far as I can tell
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*/
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#if defined(CONFIG_CPU_H8300H)
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#define start_thread(_regs, _pc, _usp) \
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do { \
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(_regs)->pc = (_pc); \
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(_regs)->ccr = 0x00; /* clear all flags */ \
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(_regs)->er5 = current->mm->start_data; /* GOT base */ \
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(_regs)->sp = ((unsigned long)(_usp)) - sizeof(unsigned long) * 3; \
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} while (0)
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#endif
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#if defined(CONFIG_CPU_H8S)
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#define start_thread(_regs, _pc, _usp) \
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do { \
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(_regs)->pc = (_pc); \
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(_regs)->ccr = 0x00; /* clear kernel flag */ \
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(_regs)->exr = 0x78; /* enable all interrupts */ \
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(_regs)->er5 = current->mm->start_data; /* GOT base */ \
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/* 14 = space for retaddr(4), vector(4), er0(4) and exr(2) on stack */ \
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(_regs)->sp = ((unsigned long)(_usp)) - 14; \
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} while (0)
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#endif
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/* Forward declaration, a strange C thing */
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struct task_struct;
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/* Free all resources held by a thread. */
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static inline void release_thread(struct task_struct *dead_task)
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{
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}
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/*
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* Return saved PC of a blocked thread.
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*/
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unsigned long thread_saved_pc(struct task_struct *tsk);
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unsigned long get_wchan(struct task_struct *p);
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#define KSTK_EIP(tsk) \
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({ \
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unsigned long eip = 0; \
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if ((tsk)->thread.esp0 > PAGE_SIZE && \
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MAP_NR((tsk)->thread.esp0) < max_mapnr) \
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eip = ((struct pt_regs *) (tsk)->thread.esp0)->pc; \
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eip; })
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#define KSTK_ESP(tsk) ((tsk) == current ? rdusp() : (tsk)->thread.usp)
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#define cpu_relax() barrier()
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#define cpu_relax_yield() cpu_relax()
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#define cpu_relax_lowlatency() cpu_relax()
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#define HARD_RESET_NOW() ({ \
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local_irq_disable(); \
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asm("jmp @@0"); \
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})
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#endif
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