Maybe the field functions are slow.
I replaced the field functions with point-min and point-max
(narrow-to-region (point-min) (point-max))
and the overhead disappeared.

Kang Niu <isgniuk@gmail.com> 于2021年12月19日周日 23:19写道：

> Seems now the let clause undertake the overhead:
>      Samples    %   Function
>
>
>         7230  77% - symbol-overlay-post-command
>         7227  77%  - if
>         7183  77%   - string=
>         7180  77%    - symbol-overlay-get-symbol
>         7180  77%     - or
>         7176  77%      - thing-at-point
>         7163  77%       - save-restriction
>         7138  76%        - let
>          221   2%         - cond
>          206   2%          + let
>            2   0%            let*
>            7   0%         + if
>           40   0%   + symbol-overlay-remove-temp
>         1234  13% - command-execute
>         1215  13%  - call-interactively
>         1205  12%   - funcall-interactively
>          783   8%    + next-line
>          415   4%    + previous-line
>            7   0%    + execute-extended-command
>            3   0%   + byte-code
>          358   3% + ...
>          255   2% + redisplay_internal (C function)
>          156   1% + timer-event-handler
>           25   0% + undo-auto--add-boundary
>           18   0% + jit-lock--antiblink-post-command
>           17   0% + internal-timer-start-idle
>            8   0% + clear-minibuffer-message
>
> Lars Ingebrigtsen <larsi@gnus.org> 于2021年12月19日周日 22:44写道：
>
>> Kang Niu <isgniuk@gmail.com> writes:
>>
>> > There are no fields in the buffer. (field-beginning) (field-end) return
>> the same value
>> > as (point-min) (point-max).
>>
>> Odd.  Does the following fix the performance problem?  I'm wondering
>> whether it's the field functions that are slow or whether the
>> narrow-to-region is the thing that somehow triggers the slowness.
>>
>> diff --git a/lisp/thingatpt.el b/lisp/thingatpt.el
>> index 2d1bf2013e..e746d94080 100644
>> --- a/lisp/thingatpt.el
>> +++ b/lisp/thingatpt.el
>> @@ -178,7 +178,11 @@ thing-at-point
>>  See the file `thingatpt.el' for documentation on how to define
>>  a symbol as a valid THING."
>>    (save-restriction
>> -    (narrow-to-region (field-beginning) (field-end))
>> +    (let ((beg (field-beginning))
>> +          (end (field-end)))
>> +      (when (or (not (= beg (point-min)))
>> +                (not (= end (point-max))))
>> +        (narrow-to-region (field-beginning) (field-end))))
>>      (let ((text
>>             (cond
>>              ((cl-loop for (pthing . function) in
>> thing-at-point-provider-alist
>>
>>
>> --
>> (domestic pets only, the antidote for overdose, milk.)
>>    bloggy blog: http://lars.ingebrigtsen.no
>>
>