Counter callback function does not always run immediately when alarm is trigged

[NineDayCC]

I use counter_set_channel_alarm to set counter alarm value and change GPIO output level in callback function.
But I found that the interval between the output level changes have a slightly different (around 0 - 15us) everytime, which is unacceptable for my program.
Is it because the kernel is doing something before callback function runs? How can I do to make the output interval run as I expected?

The counter is 1Mhz (1us). This is part of how I setup the output.

//esp32c3_devkitm
&timer0 {
    status = "ok";
    label = "PPM Timer";
    prescaler = <80>;
    group = <0>;
    index = <0>;
};

ppm_init()
{
    ...
    counter_start(counter_dev);

    alarm_cfg.flags = 1;
    alarm_cfg.ticks = counter_us_to_ticks(counter_dev, DELAY);
    alarm_cfg.callback = ppm_counter_interrupt_fn;
    alarm_cfg.user_data = &alarm_cfg;

    ret = counter_set_channel_alarm(counter_dev, ALARM_CHANNEL_ID,
                                    &alarm_cfg);
    ...
}

void ppm_counter_interrupt_fn(const struct device *counter_dev,
                                     uint8_t chan_id, uint32_t ticks,
                                     void *user_data)
{
    static const struct gpio_dt_spec ppm_dev = GPIO_DT_SPEC_GET(DT_PPM_PIN, gpios);
    static uint32_t ticks_offset = 0;    //the starting_value of a new loop

    gpio_pin_toggle_dt(&ppm_dev);    //change io output level

    if (curstep == 0)
    {
        ticks_offset = ticks;
    }

    struct counter_alarm_cfg *config = user_data;
    config->ticks = ticks_offset + interval_offset[curstep];    //add next interval_offset to the starting_value of this loop as the next alarm value

    curstep++;
    if (curstep > (sizeof(interval) / sizeof(interval[0]) ) )
    {
        curstep = 0;
    }

    counter_set_channel_alarm(counter_dev, ALARM_CHANNEL_ID, user_data);
    ...
}

The minimum interval I run between level changes is 300us. When I use logic analyzer to read the output, it's not alaways accurate 300us.

OS: zephyr 3.4.0
Toolchain: zephyr-sdk-0.16.0
Board: esp32c3_devkitm