Add a test to help track down performance changes.

2 files changed, 135 insertions, 1 deletions

diff --git a/Makefile b/Makefile
index 9771ba8..d9e4060 100644
--- a/Makefile
+++ b/Makefile
@@ -1,14 +1,20 @@
 EMACS ?= emacs
 ELFILES := perspective.el
 ELCFILES = $(ELFILES:.el=.elc)
+TESTFILES := $(wildcard test/test-*.el)
 
 all: test
 
 .PHONY: test
 test:
-	$(EMACS) -nw -Q -batch -L . -l ert $(addprefix -l ,$(wildcard test/*.el)) \
+	$(EMACS) -nw -Q -batch -L . -l ert $(addprefix -l ,$(TESTFILES)) \
 		--eval "(ert-run-tests-batch-and-exit)"
 
+.PHONY: perf
+perf:
+	$(EMACS) -nw -Q -batch -L . -l test/perf-perspective.el \
+		--eval "(persp-perf-run)"
+
 .PHONY: compile
 compile: $(ELCFILES)
 
diff --git a/test/perf-perspective.el b/test/perf-perspective.el
new file mode 100644
index 0000000..aa43352
--- /dev/null
+++ b/test/perf-perspective.el
@@ -0,0 +1,128 @@
+;;; perf-perspective.el --- Performance harness for Perspective  -*- lexical-binding: t; -*-
+
+;; Licensed under the same terms as Emacs and under the MIT license.
+
+;; URL: http://github.com/nex3/perspective-el
+;; Created: 2026-03-30
+
+;;; Commentary:
+
+;; This file provides an opt-in batch harness for comparing Perspective buffer
+;; killing behavior across revisions. It is intentionally not part of the
+;; default ERT suite.
+;;
+;; Run from the repository root with:
+;;
+;;   make perf
+;;
+;; Or directly:
+;;
+;;   emacs -Q --batch -L . -l test/perf-perspective.el --eval "(persp-perf-run)"
+;;
+;; Customize the run with:
+;;
+;;   (let ((persp-perf-num-perspectives 16)
+;;         (persp-perf-buffers-per-perspective 24)
+;;         (persp-perf-temp-buffers-per-perspective 8)
+;;         (persp-perf-iterations 15))
+;;     (persp-perf-run))
+
+;;; Code:
+
+(require 'benchmark)
+(require 'cl-lib)
+(require 'perspective)
+
+(defvar persp-perf-num-perspectives 12
+  "How many non-main perspectives to create for the performance harness.")
+
+(defvar persp-perf-buffers-per-perspective 20
+  "How many ordinary buffers to create in each perspective.")
+
+(defvar persp-perf-temp-buffers-per-perspective 6
+  "How many temporary buffers to create in each perspective.")
+
+(defvar persp-perf-iterations 10
+  "How many times to run each benchmark scenario.")
+
+(defun persp-perf--cleanup-buffers ()
+  "Kill all live buffers except the startup scratch buffer."
+  (let ((scratch (get-buffer "*scratch*")))
+    (dolist (buffer (buffer-list))
+      (when (and (buffer-live-p buffer)
+                 (not (eq buffer scratch)))
+        (kill-buffer buffer)))))
+
+(defmacro persp-perf--with-environment (&rest body)
+  "Run BODY in a fresh Perspective environment and clean up afterward."
+  (declare (indent 0))
+  `(let ((persp-suppress-no-prefix-key-warning t)
+         (persp-feature-flag-prevent-killing-last-buffer-in-perspective t))
+     (persp-perf--cleanup-buffers)
+     (persp-mode 1)
+     (unwind-protect
+         (progn ,@body)
+       (persp-mode -1)
+       (persp-perf--cleanup-buffers))))
+
+(defun persp-perf--populate-perspectives ()
+  "Populate multiple perspectives with ordinary and temporary buffers."
+  (cl-loop for idx from 1 to persp-perf-num-perspectives do
+           (let ((persp-name (format "P%d" idx)))
+             (persp-switch persp-name)
+             (cl-loop for buf-idx from 1 to persp-perf-buffers-per-perspective do
+                      (switch-to-buffer (format "*%s-buf-%02d*" persp-name buf-idx)))
+             (cl-loop for tmp-idx from 1 to persp-perf-temp-buffers-per-perspective do
+                      (switch-to-buffer (format " %s-temp-%02d" persp-name tmp-idx)))))
+  (persp-switch "main"))
+
+(defun persp-perf--scenario-unrelated-kill ()
+  "Kill a buffer from the current perspective while other perspectives are unrelated."
+  (persp-perf--with-environment
+   (persp-perf--populate-perspectives)
+   (let ((target (switch-to-buffer "*perf-target*")))
+     (switch-to-buffer "*perf-helper*")
+     (switch-to-buffer target)
+     (kill-buffer target))))
+
+(defun persp-perf--scenario-shared-keeper ()
+  "Kill a shared buffer that must remain alive in another perspective."
+  (persp-perf--with-environment
+   (let ((ido-ignore-buffers '("^\\*scratch\\*")))
+     (persp-perf--populate-perspectives)
+     (let ((target (switch-to-buffer "*perf-target*")))
+       (persp-switch "P1")
+       (switch-to-buffer target)
+       (persp-switch "main")
+       (switch-to-buffer "*perf-helper*")
+       (switch-to-buffer target)
+       (kill-buffer target)))))
+
+(defun persp-perf--benchmark (name function)
+  "Run benchmark NAME by calling FUNCTION `persp-perf-iterations' times."
+  (let ((result (benchmark-run persp-perf-iterations (funcall function))))
+    (message "%s" name)
+    (message "  iterations: %d" persp-perf-iterations)
+    (message "  elapsed:    %.6fs" (nth 0 result))
+    (message "  gc-count:   %d" (nth 1 result))
+    (message "  gc-elapsed: %.6fs" (nth 2 result))
+    (message "")))
+
+(defun persp-perf-run ()
+  "Run the Perspective performance harness in batch mode."
+  (interactive)
+  (message "Perspective performance harness")
+  (message "  perspectives: %d" persp-perf-num-perspectives)
+  (message "  regular buffers / perspective: %d" persp-perf-buffers-per-perspective)
+  (message "  temp buffers / perspective:    %d" persp-perf-temp-buffers-per-perspective)
+  (message "")
+  (persp-perf--benchmark
+   "Scenario 1: kill buffer with unrelated other perspectives"
+   #'persp-perf--scenario-unrelated-kill)
+  (persp-perf--benchmark
+   "Scenario 2: kill shared buffer that another perspective must keep"
+   #'persp-perf--scenario-shared-keeper))
+
+(provide 'perf-perspective)
+
+;;; perf-perspective.el ends here