Question about `timer base'

["Lee David" <live4thee@xxxxxxxxx>]

Hi, all

When I reading the Cascading Timer Wheel code, I found there is a
`base' field and so does in hrtimers.

struct timer_list {
      struct list_head        entry;
      unsigned long           expires;
      void                    (*function)(unsigned long);
      unsigned long           data;
      struct timer_base_s     *base;        /* timer base (1) */
};

struct hrtimer {
       struct rb_node         node;
       ktime_t                expires;
       enum hrtimer_state     state;
       int                    (*function)(void *);
       void                   *data;
       struct hrtimer_base    *base;        /* timer base (2) */
};

Can somebody pls tell me what does 'timer base' exact mean?
And what purpose does the two `base' field above used for?

Thanks in advance,
D.L.

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