Re: Default of jit-lock-stealth-time

[David Kastrup <dak@gnu.org>]

Eli Zaretskii <eliz@gnu.org> writes:

> On a 3-GHz machine, with jit-lock-stealth-time set to nil, I measure a
> consistent 5-10% increase in CPU time when paging up thru sufficiently
> long Texinfo documents wrt to an already fontified buffer (18%-25%
> percent the first time I page up, vs 10%-16% on subsequent attempts).
> By contrast, with the default setting of jit-lock-stealth-time I see
> only 1-3% of CPU being used while stealth fontification runs in the
> background, which is barely distinguishable from a totally idle
> machine.

Well, I have a 1.2GHz laptop (but the results were similar for my
previous 600MHz box).

Apart from "pathological" buffers, paging through a file will deliver
font locking fast enough to follow the user action, without causing
the laptop to use the fan.

In contrast, left alone to jit-lock-stealth-time=16, Emacs will
eventually turn to eating 100% of CPU time (not 1-3%), causing the fan
to go on and power drainage to occur.

That does not mean that the problematic files will page through
without noticeable delay when I go through them by hand: they tend to
react sluggishly to editing.  But that is a minor inconvenience
compared to the computer going unresponsible at full CPU power
frequently.

I would consider stealth fontification completely useless as long as
the computer can keep up with the user, which appears to be the case
for your usage.  In that case, investing the power when it is actually
needed seems by far the sanest choice.

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum