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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>
99 lines
2.9 KiB
C
99 lines
2.9 KiB
C
/*
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* OpenRISC Linux
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*
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* Linux architectural port borrowing liberally from similar works of
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* others. All original copyrights apply as per the original source
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* declaration.
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*
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* OpenRISC implementation:
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* Copyright (C) 2003 Matjaz Breskvar <phoenix@bsemi.com>
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* Copyright (C) 2010-2011 Jonas Bonn <jonas@southpole.se>
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* et al.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*/
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#ifndef __ASM_OPENRISC_PROCESSOR_H
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#define __ASM_OPENRISC_PROCESSOR_H
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#include <asm/spr_defs.h>
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#include <asm/page.h>
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#include <asm/ptrace.h>
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#define STACK_TOP TASK_SIZE
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#define STACK_TOP_MAX STACK_TOP
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/* Kernel and user SR register setting */
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#define KERNEL_SR (SPR_SR_DME | SPR_SR_IME | SPR_SR_ICE \
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| SPR_SR_DCE | SPR_SR_SM)
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#define USER_SR (SPR_SR_DME | SPR_SR_IME | SPR_SR_ICE \
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| SPR_SR_DCE | SPR_SR_IEE | SPR_SR_TEE)
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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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/*
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* User space process size. 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 (0x80000000UL)
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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.
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*/
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#define TASK_UNMAPPED_BASE (TASK_SIZE / 8 * 3)
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#ifndef __ASSEMBLY__
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struct task_struct;
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struct thread_struct {
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};
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/*
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* At user->kernel entry, the pt_regs struct is stacked on the top of the
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* kernel-stack. This macro allows us to find those regs for a task.
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* Notice that subsequent pt_regs stackings, like recursive interrupts
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* occurring while we're in the kernel, won't affect this - only the first
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* user->kernel transition registers are reached by this (i.e. not regs
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* for running signal handler)
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*/
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#define user_regs(thread_info) (((struct pt_regs *)((unsigned long)(thread_info) + THREAD_SIZE - STACK_FRAME_OVERHEAD)) - 1)
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/*
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* Dito but for the currently running task
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*/
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#define task_pt_regs(task) user_regs(task_thread_info(task))
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#define INIT_SP (sizeof(init_stack) + (unsigned long) &init_stack)
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#define INIT_THREAD { }
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#define KSTK_EIP(tsk) (task_pt_regs(tsk)->pc)
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#define KSTK_ESP(tsk) (task_pt_regs(tsk)->sp)
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void start_thread(struct pt_regs *regs, unsigned long nip, unsigned long sp);
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void release_thread(struct task_struct *);
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unsigned long get_wchan(struct task_struct *p);
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/*
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* Return saved PC of a blocked thread. For now, this is the "user" PC
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*/
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extern unsigned long thread_saved_pc(struct task_struct *t);
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#define init_stack (init_thread_union.stack)
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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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#endif /* __ASSEMBLY__ */
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#endif /* __ASM_OPENRISC_PROCESSOR_H */
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