magit.el

(defun magit-perf-log (msg)
  "Log a msg to the magit perf log"
  (flet ((message (&rest args) (ignore)))
    (with-temp-buffer
      (insert msg)
      (append-to-file (point-min)
                      (point-max)
                      "/tmp/magit-perf-log.txt"))))

(defun magit-cmd-output (cmd args)
  (let ((time-before (float-time)))
    (magit-perf-log (format "Running %s %s\n" cmd args))
    (with-output-to-string
      (with-current-buffer standard-output
        (apply #'process-file
               cmd
               nil (list t nil) nil
               args)))
    (magit-perf-log (format "%s %s  --> Elapsed: %f seconds\n"
                            cmd
                            args
                            (- (float-time)
                               time-before)))))