This version is actually slightly faster... And the sys time goes down
very close to zero.
Now, what were you actually looking to test??
My version might be utterly irrelevant.
function BashCount() {
i=$1
while (( i-- )) ; do
true
done
echo Just did $1 iterations using bash math
}
time BashCount 150000
On 2013-03-17 07:31, Pierre Gaston wrote:
On Sun, Mar 17, 2013 at 4:33 AM, Bruce Dawson
<brucedaw...@cygnus-software.com> wrote:
Thanks -- good to know that there is a fast and POSIX compliant method of
doing this. I should have included my optimized counting loop -- it's what
we switched to when we realized that $(expr) was a problem. Here it is now:
# This code performs quite well
function BashCount() {
i=$1
while [ $i -gt 0 ]; do
(( i-- ))
done
echo Just did $1 iterations using bash math
}
time BashCount 150000
It's a *lot* faster, of course. BTW, I've poked around in the 'time' source
code enough to know that it is just displaying the results of wait3(), so
the misleading CPU consumption information is ultimately a wait3()/kernel
issue. However showing this in the documentation would be great.
At least the man page of time on my ubuntu system is pretty much clear
about what it does.
The result is not striking me as impossible though, I can imagine a
lot of real time spent waiting for the scheduler to run expr and then
to run bash again.
I tried a little experiment that I think shows the importance of the
scheduler on the real time result:
I run at the same time this little loop with different "niceness"
i=0;time while ((i++<10000));do /bin/echo -n;done
sudo nice -n 19 bash -c 'i=0;time while ((i++<10000));do /bin/echo
-n;done' 2>&1| sed s/^/19:\ / &
sudo nice -n -20 bash -c 'i=0;time while ((i++<10000));do /bin/echo
-n;done' 2>&1| sed s/^/-20:\ /
I get:
-20: real 0m9.331s
-20: user 0m0.468s
-20: sys 0m1.504s
19: real 0m14.004s
19: user 0m0.532s
19: sys 0m1.660s
so the nicer loop takes twice as much real time indicating that much
real time is spent waiting for the process to run.
