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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>
96 lines
2.4 KiB
C
96 lines
2.4 KiB
C
/*
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* Copyright (C) 2013 Altera Corporation
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* Copyright (C) 2010 Tobias Klauser <tklauser@distanz.ch>
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* Copyright (C) 2004 Microtronix Datacom Ltd
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* Copyright (C) 2001 Ken Hill (khill@microtronix.com)
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* Vic Phillips (vic@microtronix.com)
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*
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* based on SPARC asm/processor_32.h which is:
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*
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* Copyright (C) 1994 David S. Miller
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*
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* This file is subject to the terms and conditions of the GNU General Public
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* License. See the file "COPYING" in the main directory of this archive
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* for more details.
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*/
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#ifndef _ASM_NIOS2_PROCESSOR_H
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#define _ASM_NIOS2_PROCESSOR_H
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#include <asm/ptrace.h>
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#include <asm/registers.h>
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#include <asm/page.h>
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#define NIOS2_FLAG_KTHREAD 0x00000001 /* task is a kernel thread */
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#define NIOS2_OP_NOP 0x1883a
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#define NIOS2_OP_BREAK 0x3da03a
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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 /* __KERNEL__ */
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/* Kuser helpers is mapped to this user space address */
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#define KUSER_BASE 0x1000
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#define KUSER_SIZE (PAGE_SIZE)
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#ifndef __ASSEMBLY__
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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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# define TASK_SIZE 0x7FFF0000UL
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# define TASK_UNMAPPED_BASE (PAGE_ALIGN(TASK_SIZE / 3))
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/* The Nios processor specific thread struct. */
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struct thread_struct {
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struct pt_regs *kregs;
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/* Context switch saved kernel state. */
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unsigned long ksp;
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unsigned long kpsr;
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};
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#define INIT_MMAP \
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{ &init_mm, (0), (0), __pgprot(0x0), VM_READ | VM_WRITE | VM_EXEC }
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# define INIT_THREAD { \
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.kregs = NULL, \
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.ksp = 0, \
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.kpsr = 0, \
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}
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extern void start_thread(struct pt_regs *regs, unsigned long pc,
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unsigned long sp);
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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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/* Return saved PC of a blocked thread. */
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#define thread_saved_pc(tsk) ((tsk)->thread.kregs->ea)
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extern unsigned long get_wchan(struct task_struct *p);
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#define task_pt_regs(p) \
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((struct pt_regs *)(THREAD_SIZE + task_stack_page(p)) - 1)
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/* Used by procfs */
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#define KSTK_EIP(tsk) ((tsk)->thread.kregs->ea)
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#define KSTK_ESP(tsk) ((tsk)->thread.kregs->sp)
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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_NIOS2_PROCESSOR_H */
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