linux – current_kernel_time()的可靠性如何？

大多数时候我得到时间差为0(零)纳秒(不管读/写数据的大小：16-2048字节),从逻辑上我认为是不正确的,只有极少数我得到一些值,希望那些是正确.

current_kernel_time()的可靠性如何？

为什么我大多数时间都会获得0ns？

我打算在内核级别进行分析以获得更多细节.在此之前,有人可以对这种行为有所了解……之前有人观察过这样的事情……

此外,欢迎任何帮助/纠正我的基准测试方法的建议！

谢谢.

编辑：
这是Linux内核版本2.6.32.9的读取代码.我在#ifdef-endif下添加了current_kernel_time(),如下所示：

static void sdio_uart_receive_chars(struct sdio_uart_port *port,unsigned int *status)
{
#ifdef SDIO_UART_DEBUG
struct timespec time_spec1,time_spec2;
time_spec1 = current_kernel_time();
#endif

    struct tty_struct *tty = port->tty;
    unsigned int ch,flag;
    int max_count = 256;

    do {
        ch = sdio_in(port,UART_RX);
        flag = TTY_NORMAL;
        port->icount.rx++;

        if (unlikely(*status & (UART_LSR_BI | UART_LSR_PE |
                        UART_LSR_FE | UART_LSR_OE))) {
            /*
             * For statistics only
             */
            if (*status & UART_LSR_BI) {
                *status &= ~(UART_LSR_FE | UART_LSR_PE);
                port->icount.brk++;
            } else if (*status & UART_LSR_PE)
                port->icount.parity++;
            else if (*status & UART_LSR_FE)
                port->icount.frame++;
            if (*status & UART_LSR_OE)
                port->icount.overrun++;

            /*
             * Mask off conditions which should be ignored.
             */
            *status &= port->read_status_mask;
            if (*status & UART_LSR_BI) {
                flag = TTY_BREAK;
            } else if (*status & UART_LSR_PE)
                flag = TTY_PARITY;
            else if (*status & UART_LSR_FE)
                flag = TTY_FRAME;
        }

        if ((*status & port->ignore_status_mask & ~UART_LSR_OE) == 0)
            tty_insert_flip_char(tty,ch,flag);

        /*
         * Overrun is special.  Since it's reported immediately,* it doesn't affect the current character.
         */
        if (*status & ~port->ignore_status_mask & UART_LSR_OE)
            tty_insert_flip_char(tty,TTY_OVERRUN);

        *status = sdio_in(port,UART_LSR);
    } while ((*status & UART_LSR_DR) && (max_count-- > 0));
    tty_flip_buffer_push(tty);

#ifdef SDIO_UART_DEBUG
time_spec2 = current_kernel_time();
printk(KERN_INFO "n MY_DBG : read took: %ld nanoseconds",(time_spec2.tv_sec  - time_spec1.tv_sec) * 1000000000 + (time_spec2.tv_nsec - time_spec1.tv_nsec));
#endif

}