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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>
121 lines
3.2 KiB
C
121 lines
3.2 KiB
C
/* processor.h: FRV processor definitions
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*
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* Copyright (C) 2003 Red Hat, Inc. All Rights Reserved.
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* Written by David Howells (dhowells@redhat.com)
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version
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* 2 of the License, or (at your option) any later version.
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*/
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#ifndef _ASM_PROCESSOR_H
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#define _ASM_PROCESSOR_H
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#include <asm/mem-layout.h>
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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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#include <linux/compiler.h>
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#include <linux/linkage.h>
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#include <asm/sections.h>
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#include <asm/segment.h>
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#include <asm/fpu.h>
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#include <asm/registers.h>
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#include <asm/ptrace.h>
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#include <asm/current.h>
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#include <asm/cache.h>
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/* Forward declaration, a strange C thing */
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struct task_struct;
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/*
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* Bus types
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*/
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#define EISA_bus 0
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struct thread_struct {
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struct pt_regs *frame; /* [GR28] exception frame ptr for this thread */
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struct task_struct *curr; /* [GR29] current pointer for this thread */
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unsigned long sp; /* [GR1 ] kernel stack pointer */
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unsigned long fp; /* [GR2 ] kernel frame pointer */
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unsigned long lr; /* link register */
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unsigned long pc; /* program counter */
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unsigned long gr[12]; /* [GR16-GR27] */
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unsigned long sched_lr; /* LR from schedule() */
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union {
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struct pt_regs *frame0; /* top (user) stack frame */
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struct user_context *user; /* userspace context */
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};
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} __attribute__((aligned(8)));
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extern struct pt_regs *__kernel_frame0_ptr;
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extern struct task_struct *__kernel_current_task;
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#endif
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#ifndef __ASSEMBLY__
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#define INIT_THREAD_FRAME0 \
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((struct pt_regs *) \
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(sizeof(init_stack) + (unsigned long) init_stack - sizeof(struct user_context)))
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#define INIT_THREAD { \
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NULL, \
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(struct task_struct *) init_stack, \
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0, 0, 0, 0, \
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{ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 }, \
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0, \
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{ INIT_THREAD_FRAME0 }, \
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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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#define start_thread(_regs, _pc, _usp) \
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do { \
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_regs->pc = (_pc); \
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_regs->psr &= ~PSR_S; \
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_regs->sp = (_usp); \
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} while(0)
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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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extern asmlinkage void save_user_regs(struct user_context *target);
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extern asmlinkage void *restore_user_regs(const struct user_context *target, ...);
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#define copy_segments(tsk, mm) do { } while (0)
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#define release_segments(mm) do { } while (0)
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#define forget_segments() do { } while (0)
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/*
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* Return saved PC of a blocked thread.
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*/
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extern 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) ((tsk)->thread.frame0->pc)
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#define KSTK_ESP(tsk) ((tsk)->thread.frame0->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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/* data cache prefetch */
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#define ARCH_HAS_PREFETCH
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static inline void prefetch(const void *x)
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{
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asm volatile("dcpl %0,gr0,#0" : : "r"(x));
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}
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#endif /* __ASSEMBLY__ */
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#endif /* _ASM_PROCESSOR_H */
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