[tex-live] strange discrepancy in running time of etex between TL2015 and TL2017
jfbu at free.fr
Sat Jul 29 10:07:16 CEST 2017
Le 29 juil. 2017 à 02:07, Reinhard Kotucha <reinhard.kotucha at web.de> a écrit :
> On 2017-07-28 at 09:15:32 +0200, jfbu wrote:
>> minutes: for very lengthy things (5mns+) my laptop *slows down* in
>> comparison to the desktop or the Linux machine
> Hi Jean-Francois,
> the CPU fan is obviously not able to keep the CPU temperature below a
> certain limit. In order to prevent the CPU from being destroyed by
> heat, the clock frequency is reduced. This is intended and expected
> Power consumption increases linearly with clock frequency. If your
> CPU gets too hot, your system has only two choices: either reduce the
> clock frequency or shutdown the system completely.
somehow, I sort of did not quite think it out this way because
I observed the phenomenon with computations lasting of the order
of one minute, but my fan gets started for longer computations
of at least seven or eight minutes. But I think you must
be right. (anyway there must be _some_ explanation ;-) I was
thinking perhaps some virtual memory thing, but I have an SSD
only on my laptop)
> You can check yourself: Before starting your program, open another
> terminal window and run
> while true; do clear; grep 'cpu MHz' /proc/cpuinfo; sleep 1; done
> therein. This works at least on Linux. On OS X you probably have to
> run "sysctl -a" and check whether the current CPU frequencies are
> reported. I don't have OS X.
yes sysctl -a seems report quite a bunch of cpu information
I see things like
machdep.cpu.brand_string: Intel(R) Core(TM) i7-3667U CPU @ 2.00GHz
I have not tried yet to use dynamically
> I suppose that the CPU frequencies are quite low at the beginnig, when
> no other processes are running. When you start your program, at least
> one CPU will run at full speed. After a while, when your system gets
> slower, you'll see that CPU frequencies are decreased. You'll also
> notice that the air coming from the CPU fan is extremely hot.
I will try to investigate if CPU frequency is adapted
> The problem is that laptops are almost as powerful as desktop PCs but
> there is not enough space for a decent cooling system. This is quite
> unfortunate because lifetime of electronic components heavily depend
> on temperature.
> BTW, I encountered a peculiarity with my Linux machine a few years
> ago. I could do everything with this machine -- except compiling gcc.
> Whenever I invoked "./configure && make -j3", the power supply turned
> off after a few minutes. In this case the power supply was too weak
> and replacing it by a bigger one solved the problem.
Lucky you not with Mac: you can replace things.
Here my batteries are 5 years old and changing them is way overdue
but I must bring the thing to an Apple Store, for this I need
to make an appointment, then they want to charge me something
like 200 euros (don't recall the details; but definitely it
is something like at least 50 euros for the physical replacement
not the price of batteries; and if I wait too long possibly
the battery model will not exist anymore).
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