[tex-live] strange discrepancy in running time of etex between TL2015 and TL2017

jfbu jfbu at free.fr
Fri Jul 28 09:15:32 CEST 2017

Le 28 juil. 2017 at 03:26, Reinhard Kotucha <reinhard.kotucha at web.de> :

> On 2017-07-27 at 08:58:43 +0200, jfbu wrote:
>> Thanks a lot for trying out, the most likely cause is that the 
>> def\x{3.141592653589793238462....
>> line got hard-wrapped somehow so that it occupies multiple lines
>> (it should be on only one line)
>> and this means the \x has spaces in it and the \ifx test fails
>> because the \Z computed by \fdef\Z {\Machin {1000}} contains
>> the first 1000 digits of Pi with no spaces.
> The problem was that the value of \x contained three spurious
> characters (numbers are code points):
>  0039: DIGIT NINE
>  0032: DIGIT TWO
>  0037: DIGIT SEVEN
>  0038: DIGIT EIGHT
>  0037: DIGIT SEVEN
>  000A: <control> LINE FEED (LF)
>  0020: SPACE
>  0036: DIGIT SIX
>  0036: DIGIT SIX
>  0031: DIGIT ONE
>  0031: DIGIT ONE
>  0031: DIGIT ONE
> I do not know where these characters had been inserted.  But if you
> send code by mail which contains non-ASCII characters and/or where
> linebreaks matter, I strongly recommend to send the file as an email
> attachment.  It's also advisable to gzip the file because it's marked
> as "application/octet-stream" then by your mail client.

Thanks for confirming the corruption of \x

visiting with Firefox


I don't see the extra ! CTRL-J SPACE. But certainly I should have
sent the file as binary to avoid any such problem with a line of 
1000 or so characters.

On arXiv of old years, and even on CTAN, one could find
many many latex file or dtx files containing "> From" at start
of lines. The original had only "From" and the mailer inserted the "> ".

People collaborating on a paper send versions by mail, hence
it might even be that a very large proportion of math papers in the
nineties got corrugated in this way.

(I have forgotten now, perhaps it was in fact also related to ftp

> You can trust \pdfelapsedtime because it just uses system calls but I
> don't know which system call is used by pdftex.  It seems that it's
> based on gettimeofday(2).

I have lots of experimenting with \pdfelapsedtime on Mac OS and
also a bit on Linux, and it has always stricken me as quite fluctuating
even when used for durations of tens of seconds.

One such source is definitely deep in the CPU management, because
on my laptop I have a specific phenomenon which I do not observe
on a Mac desktop regarding computation times when running into
minutes: for very lengthy things (5mns+) my laptop *slows down*
in comparison to the desktop or the Linux machine

> Luatex provides os.clock() and os.gettimeofday().
> os.clock() counts CPU cycles of the current process with a resolution
> of 10 ms.  It disregards CPU cycles used by sub-processes or other
> processes running at the same time.
> os.gettimeofday(), as its name implies, just returns the current time
> and is less reliable when a cronjob is running or Emacs creates an
> auto-backup.  The resolution is system dependent (1µs on Linux and
> 500µs on Windows).  Don't be confused by the many decimal digits.
> Most of them are just rounding errors which are almost always
> introduced when binary numbers are converted to the decimal system.
> See also
>  https://www.tug.org/TUGboat/tb28-3/tb90beebe.pdf

Thanks for the link I will check it out.

> If you are using \pdfelapsedtime, os.clock(), or os.gettimeofday(), it
> doesn't matter whether any files are cached already, at least if your
> input file resets the counter at the beginning and you avoid \input.
> IMO it's best to use os.clock() on LuaTeX for benchmarks despite its
> low resolution.  The problem you reported is OS/X specific but in most
> cases a resolution of 10 ms is sufficient on a Raspberry Pi.
> If you are using time(1), which depends on gettimeofday(2), you have
> to run the script several times because other processes might run in
> the background.  It's also advisable to install a system monitor like
> xosview.

When I need to be a bit serious and not only get a general impression
I indeed try to run the test in a controlled environment:

- turn off the wifi, hence all internet

- kill all apps beyond Terminal

- run on house electric power, not on batteries

In my experience on Mac OSes, \pdfelapsedtime has some
significant fluctuations when I use it multiple times in the same
TeX job, 

Some years ago I was usually simply sending \the\pdfelapsedtime
to PDF output
and I noticed I should do a \noindent before \pdfresettimer
to get things a bit stabilized between multiple uses
of \pdfelapsedtime in same TeX run

nowadays I work more likely with log or terminal output,
and when I want to get serious I do not use Emacs AUCTeX,
because I noticed that it significantly slows down compilation
time, presumably from its on-the-fly parsing of log output,
when this log output is voluminous (which in LaTeX it always
is to some extent)

With "time", I get relatively stable and coherent results with 
the occasional extravagancy when the system did something
strange like sending to the NSA or to my ISP provider
all my private data, or perhaps my computer is talking with 
Apple servers or whatever Google Analytics.

But globally "time" has always given me more coherent results
than "\pdfelapsedtime".



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