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From: Simon Marshall <Simon.Marshall@esrin.esa.it>
To: XEmacs Beta <xemacs-beta@xemacs.org>
In-Reply-To: <yv9bu99hlkq.fsf@ynde.idt.unit.no> (message from Sudeep Kumar
	Palat on 24 Feb 1997 23:43:17 +0100)
Subject: Re: lazy lock cpu usage
Reply-To: Simon Marshall <Simon.Marshall@esrin.esa.it>

Sudeep> Start xemacs -q and load a large file, for e.g., gnus.el.  Turn on
Sudeep> font lock.  Hold down the cursor key and look at cpu usage (I used
Sudeep> top).  When the buffer has scrolled down 20%, the cpu usage by
Sudeep> XEmacs is about 14% (it keeps increasing, presumably because,
Sudeep> XEmacs is unable to process the key input at the keyboard repeat
Sudeep> rate).

So with Font Lock mode and without Lazy Lock mode has a dramatic slowdown?

Sudeep> Turn on lazy lock, and repeat.  Scrolling 20% down, the cpu usage
Sudeep> has shot up to about 50%.

I don't have an XEmacs 20, only XEmacs 19.15b95.

With lazy-lock-hide-invisible non-nil (the default for XEmacs)
lazy-lock.el version 1 always does more work since it cannot rely on
window-start and window-end.  So I would expect a slowdown, though the
scale of it is a bit surprising.  Not surprisingly, the slowdown is
reduced if the areas into which you scroll are already fontified.

Ta, Si.

