linux_kernel/tools/virtio/ringtest/main.h

/*
 * Copyright (C) 2016 Red Hat, Inc.
 * Author: Michael S. Tsirkin <mst@redhat.com>
 * This work is licensed under the terms of the GNU GPL, version 2.
 *
 * Common macros and functions for ring benchmarking.
 */
#ifndef MAIN_H
#define MAIN_H

#include <stdbool.h>

extern int param;

extern bool do_exit;

#if defined(__x86_64__) || defined(__i386__)
#include "x86intrin.h"

static inline void wait_cycles(unsigned long long cycles)
{
	unsigned long long t;

	t = __rdtsc();
	while (__rdtsc() - t < cycles) {}
}

#define VMEXIT_CYCLES 500
#define VMENTRY_CYCLES 500

#elif defined(__s390x__)
static inline void wait_cycles(unsigned long long cycles)
{
	asm volatile("0: brctg %0,0b" : : "d" (cycles));
}

/* tweak me */
#define VMEXIT_CYCLES 200
#define VMENTRY_CYCLES 200

#else
static inline void wait_cycles(unsigned long long cycles)
{
	_Exit(5);
}
#define VMEXIT_CYCLES 0
#define VMENTRY_CYCLES 0
#endif

static inline void vmexit(void)
{
	if (!do_exit)
		return;
	
	wait_cycles(VMEXIT_CYCLES);
}
static inline void vmentry(void)
{
	if (!do_exit)
		return;
	
	wait_cycles(VMENTRY_CYCLES);
}

/* implemented by ring */
void alloc_ring(void);
/* guest side */
int add_inbuf(unsigned, void *, void *);
void *get_buf(unsigned *, void **);
void disable_call();
bool used_empty();
bool enable_call();
void kick_available();
/* host side */
void disable_kick();
bool avail_empty();
bool enable_kick();
bool use_buf(unsigned *, void **);
void call_used();

/* implemented by main */
extern bool do_sleep;
void kick(void);
void wait_for_kick(void);
void call(void);
void wait_for_call(void);

extern unsigned ring_size;

/* Compiler barrier - similar to what Linux uses */
#define barrier() asm volatile("" ::: "memory")

/* Is there a portable way to do this? */
#if defined(__x86_64__) || defined(__i386__)
#define cpu_relax() asm ("rep; nop" ::: "memory")
#elif defined(__s390x__)
#define cpu_relax() barrier()
#else
#define cpu_relax() assert(0)
#endif

extern bool do_relax;

static inline void busy_wait(void)
{
	if (do_relax)
		cpu_relax();
	else
		/* prevent compiler from removing busy loops */
		barrier();
} 

#if defined(__x86_64__) || defined(__i386__)
#define smp_mb()     asm volatile("lock; addl $0,-132(%%rsp)" ::: "memory", "cc")
#else
/*
 * Not using __ATOMIC_SEQ_CST since gcc docs say they are only synchronized
 * with other __ATOMIC_SEQ_CST calls.
 */
#define smp_mb() __sync_synchronize()
#endif

/*
 * This abuses the atomic builtins for thread fences, and
 * adds a compiler barrier.
 */
#define smp_release() do { \
    barrier(); \
    __atomic_thread_fence(__ATOMIC_RELEASE); \
} while (0)

#define smp_acquire() do { \
    __atomic_thread_fence(__ATOMIC_ACQUIRE); \
    barrier(); \
} while (0)

#if defined(__i386__) || defined(__x86_64__) || defined(__s390x__)
#define smp_wmb() barrier()
#else
#define smp_wmb() smp_release()
#endif

#ifdef __alpha__
#define smp_read_barrier_depends() smp_acquire()
#else
#define smp_read_barrier_depends() do {} while(0)
#endif

static __always_inline
void __read_once_size(const volatile void *p, void *res, int size)
{
        switch (size) {                                                 \
        case 1: *(unsigned char *)res = *(volatile unsigned char *)p; break;              \
        case 2: *(unsigned short *)res = *(volatile unsigned short *)p; break;            \
        case 4: *(unsigned int *)res = *(volatile unsigned int *)p; break;            \
        case 8: *(unsigned long long *)res = *(volatile unsigned long long *)p; break;            \
        default:                                                        \
                barrier();                                              \
                __builtin_memcpy((void *)res, (const void *)p, size);   \
                barrier();                                              \
        }                                                               \
}

static __always_inline void __write_once_size(volatile void *p, void *res, int size)
{
	switch (size) {
	case 1: *(volatile unsigned char *)p = *(unsigned char *)res; break;
	case 2: *(volatile unsigned short *)p = *(unsigned short *)res; break;
	case 4: *(volatile unsigned int *)p = *(unsigned int *)res; break;
	case 8: *(volatile unsigned long long *)p = *(unsigned long long *)res; break;
	default:
		barrier();
		__builtin_memcpy((void *)p, (const void *)res, size);
		barrier();
	}
}

#define READ_ONCE(x) \
({									\
	union { typeof(x) __val; char __c[1]; } __u;			\
	__read_once_size(&(x), __u.__c, sizeof(x));		\
	smp_read_barrier_depends(); /* Enforce dependency ordering from x */ \
	__u.__val;							\
})

#define WRITE_ONCE(x, val) \
({							\
	union { typeof(x) __val; char __c[1]; } __u =	\
		{ .__val = (typeof(x)) (val) }; \
	__write_once_size(&(x), __u.__c, sizeof(x));	\
	__u.__val;					\
})

#endif