2019-12-18 DPDK开启HPET高精度时钟

/**
 * Get the number of cycles since boot from the default timer.
 *
 * @return
 *   The number of cycles
 */
static inline uint64_t
rte_get_timer_cycles(void)
{
#ifdef RTE_LIBEAL_USE_HPET
    switch(eal_timer_source) {
    case EAL_TIMER_TSC:
#endif
        return rte_get_tsc_cycles();
#ifdef RTE_LIBEAL_USE_HPET
    case EAL_TIMER_HPET:
        return rte_get_hpet_cycles();
    default: rte_panic("Invalid timer source specified\n");
    }
#endif
}

• rte_get_timer_cycles()
• rte_get_hpet_cycles()

dpdk推荐使用rte_get_timer_cycles()和rte_get_timer_hz()API来替代HPET的特有API；如果一个应用使用了rte_get_hpet_cycles()和rte_get_hpet_hz()的API接口……

image.png

DPDK开启HPET高精度时钟

• 原文地址： http://doc.dpdk.org/guides/linux_gsg/enable_func.html#enabling-additional-functionality

默认情况下，HPET在DPDK编译的时候默认是disabled。如果需要开启，那么在编译的配置文件中CONFIG_RTE_LIBEAL_USE_HPET的配置项需要写成Y。这样在编译的时候会将HPET编译进DPDK。

如果一个应用使用了rte_get_hpet_cycles()和rte_get_hpet_hz()的API接口，可以选择使用HPET来为rte_time库提供默认的时间源。在dpdk被初始化的阶段新的rte_eal_hpet_init()接口会被调用。rte_eal_hpet_init()API会确认HPET是用的，如果HPET无法使用则该接口会抛出一个错误异常返回给dpdk。举个例子，如果HPET_MMAP没有在内核中被加载，不能作为计时来使用，dpdk会决定采取接下来的行为。

针对dpdk来说需要时间的API，但是作为时间源来说HPET并不是唯一提供的时间源。dpdk推荐使用rte_get_timer_cycles()和rte_get_timer_hz()`API来替代HPET的特有API。通用类型的API可以针对TSC和HPET时间源来工作。这取决于dpdk是否请求调用rte_eal_hpet_init()，如果有的话是什么时间源运行在操作系统上。

/* SPDX-License-Identifier: BSD-3-Clause
 * Copyright(c) 2010-2014 Intel Corporation.
 * Copyright(c) 2013 6WIND S.A.
 */

#ifndef _RTE_CYCLES_H_
#define _RTE_CYCLES_H_

/**
 * @file
 *
 * Simple Time Reference Functions (Cycles and HPET).
 */

#include 
#include 
#include 
#include 

#define MS_PER_S 1000
#define US_PER_S 1000000
#define NS_PER_S 1000000000

enum timer_source {
    EAL_TIMER_TSC = 0,
    EAL_TIMER_HPET
};
extern enum timer_source eal_timer_source;

/**
 * Get the measured frequency of the RDTSC counter
 *
 * @return
 *   The TSC frequency for this lcore
 */
uint64_t
rte_get_tsc_hz(void);

/**
 * Return the number of TSC cycles since boot
 *
  * @return
 *   the number of cycles
 */
static inline uint64_t
rte_get_tsc_cycles(void);

#ifdef RTE_LIBEAL_USE_HPET
/**
 * Return the number of HPET cycles since boot
 *
 * This counter is global for all execution units. The number of
 * cycles in one second can be retrieved using rte_get_hpet_hz().
 *
 * @return
 *   the number of cycles
 */
uint64_t
rte_get_hpet_cycles(void);

/**
 * Get the number of HPET cycles in one second.
 *
 * @return
 *   The number of cycles in one second.
 */
uint64_t
rte_get_hpet_hz(void);

/**
 * Initialise the HPET for use. This must be called before the rte_get_hpet_hz
 * and rte_get_hpet_cycles APIs are called. If this function does not succeed,
 * then the HPET functions are unavailable and should not be called.
 *
 * @param make_default
 *  If set, the hpet timer becomes the default timer whose values are
 *  returned by the rte_get_timer_hz/cycles API calls
 *
 * @return
 *  0 on success,
 *  -1 on error, and the make_default parameter is ignored.
 */
int rte_eal_hpet_init(int make_default);

#endif

/**
 * Get the number of cycles since boot from the default timer.
 *
 * @return
 *   The number of cycles
 */
static inline uint64_t
rte_get_timer_cycles(void)
{
#ifdef RTE_LIBEAL_USE_HPET
    switch(eal_timer_source) {
    case EAL_TIMER_TSC:
#endif
        return rte_get_tsc_cycles();
#ifdef RTE_LIBEAL_USE_HPET
    case EAL_TIMER_HPET:
        return rte_get_hpet_cycles();
    default: rte_panic("Invalid timer source specified\n");
    }
#endif
}

/**
 * Get the number of cycles in one second for the default timer.
 *
 * @return
 *   The number of cycles in one second.
 */
static inline uint64_t
rte_get_timer_hz(void)
{
#ifdef RTE_LIBEAL_USE_HPET
    switch(eal_timer_source) {
    case EAL_TIMER_TSC:
#endif
        return rte_get_tsc_hz();
#ifdef RTE_LIBEAL_USE_HPET
    case EAL_TIMER_HPET:
        return rte_get_hpet_hz();
    default: rte_panic("Invalid timer source specified\n");
    }
#endif
}
/**
 * Wait at least us microseconds.
 * This function can be replaced with user-defined function.
 * @see rte_delay_us_callback_register
 *
 * @param us
 *   The number of microseconds to wait.
 */
extern void
(*rte_delay_us)(unsigned int us);

/**
 * Wait at least ms milliseconds.
 *
 * @param ms
 *   The number of milliseconds to wait.
 */
static inline void
rte_delay_ms(unsigned ms)
{
    rte_delay_us(ms * 1000);
}

/**
 * Blocking delay function.
 *
 * @param us
 *   Number of microseconds to wait.
 */
void rte_delay_us_block(unsigned int us);

/**
 * Delay function that uses system sleep.
 * Does not block the CPU core.
 *
 * @param us
 *   Number of microseconds to wait.
 */
__rte_experimental
void
rte_delay_us_sleep(unsigned int us);

/**
 * Replace rte_delay_us with user defined function.
 *
 * @param userfunc
 *   User function which replaces rte_delay_us. rte_delay_us_block restores
 *   builtin block delay function.
 */
void rte_delay_us_callback_register(void(*userfunc)(unsigned int));

#endif /* _RTE_CYCLES_H_ */