The Emacs master is much slower than the emacs-27 branch.

[Alan Mackenzie]

Hello, Emacs.

I've got pretty much up to date copies of both the master and the
emacs-27 branches.

When I run my customary benchmark (see below) on master's src/xdisp.c in
master, it's taking around 34s.  On emacs-27, it's taking 22s.

That's a massive slowdown.  Does anybody know why this is happening?
Should I raise a bug report?

The benchmark I run is this:

(defmacro time-it (&rest forms)
  "Time the running of a sequence of forms using `float-time'.
Call like this: \"M-: (time-it (foo ...) (bar ...) ...)\"."
  `(let ((start (float-time)))
    ,@forms
    (- (float-time) start)))

(defun time-scroll (&optional arg)
  (interactive "P")
  (message "%s"
           (time-it
            (condition-case nil
                (while t
                  (if arg (scroll-down) (scroll-up))
                  (sit-for 0))
              (error nil)))))

On a freshly loaded buffer, do M-: (time-scroll).

-- 
Alan Mackenzie (Nuremberg, Germany).