diff --git a/packages/turndown-plugin-gfm/src/tables.js b/packages/turndown-plugin-gfm/src/tables.js
index 10909ec8a..01aeca510 100644
--- a/packages/turndown-plugin-gfm/src/tables.js
+++ b/packages/turndown-plugin-gfm/src/tables.js
@@ -5,6 +5,11 @@ var alignMap = { left: ':---', right: '---:', center: ':---:' };
 
 let isCodeBlock_ = null;
 
+// We need to cache the result of tableShouldBeSkipped() as it is expensive.
+// Caching it means we went from about 9000 ms for rendering down to 90 ms.
+// Fixes https://github.com/laurent22/joplin/issues/6736 
+const tableShouldBeSkippedCache_ = new Map();
+
 function getAlignment(node) {
   return node ? (node.getAttribute('align') || node.style.textAlign || '').toLowerCase() : '';
 }
@@ -188,11 +193,20 @@ const tableShouldBeHtml = (tableNode) => {
 // Various conditions under which a table should be skipped - i.e. each cell
 // will be rendered one after the other as if they were paragraphs.
 function tableShouldBeSkipped(tableNode) {
-  if (!tableNode) return true;
-  if (!tableNode.rows) return true;
-  if (tableNode.rows.length === 1 && tableNode.rows[0].childNodes.length <= 1) return true; // Table with only one cell
-  if (nodeContainsTable(tableNode)) return true;
-  return false;
+  const cached = tableShouldBeSkippedCache_.get(tableNode);
+  if (cached !== undefined) return cached;
+
+  const process = () => {
+    if (!tableNode) return true;
+    if (!tableNode.rows) return true;
+    if (tableNode.rows.length === 1 && tableNode.rows[0].childNodes.length <= 1) return true; // Table with only one cell
+    if (nodeContainsTable(tableNode)) return true;
+    return false;
+  }
+
+  const result = process();
+  tableShouldBeSkippedCache_.set(tableNode, result);
+  return result;
 }
 
 function nodeParentTable(node) {
diff --git a/packages/utils/time.ts b/packages/utils/time.ts
index 2f2053cca..3d7e14c8d 100644
--- a/packages/utils/time.ts
+++ b/packages/utils/time.ts
@@ -1,5 +1,22 @@
-/* eslint-disable import/prefer-default-export */
-
 export const msleep = (ms: number) => {
 	return new Promise(resolve => setTimeout(resolve, ms));
 };
+
+// Use the utility functions below to easily measure performance of a block or
+// line of code.
+interface PerfTimer {
+	name: string;
+	startTime: number;
+}
+
+const perfTimers_: PerfTimer[] = [];
+
+export function timerPush(name: string) {
+	perfTimers_.push({ name, startTime: Date.now() });
+}
+
+export function timerPop() {
+	const t = perfTimers_.pop() as PerfTimer;
+	// eslint-disable-next-line no-console
+	console.info(`Time: ${t.name}: ${Date.now() - t.startTime}`);
+}