Single-run while makes script fast

Single-run while makes script fast

[Sebastian Gniazdowski]

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Hello,
I attach animated gif showing the effect. The while loop in following
code makes whole script fast:

loop=1
while (( loop -- )); do
    filename="lsoflsof" # 89k elements
    body=( "${(@f)"$(<"$filename" )"}" )
done

Commenting out the loop and leaving only its body makes the whole script slow:

loop=1
#while (( loop -- )); do
    filename="lsoflsof" # 89k elements
    body=( "${(@f)"$(<"$filename" )"}" )
#done

This is reveals on Zsh 5.0.8 (OS X). On 5.2 it isn't visible or
doesn't actually occur – because of recent optimizations.

I wasn't able to reproduce this in some short script, but might yet
try to do this. I'm reporting because maybe there is something hidden
behind this.

Best regards,
Sebastian Gniazdowski

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Re: Single-run while makes script fast

[Sebastian Gniazdowski]

I tested this on my two other scripts and it's speeding things up also
there. Already commited the "optimizations":

https://github.com/psprint/zsh-navigation-tools/commit/71fe5a2227a4e8a116878194bf2bbb6db1bb8c25

Best regards,
Sebastian Gniazdowski


On 4 December 2015 at 17:20, Sebastian Gniazdowski
<sgniazdowski@gmail.com> wrote:
> Hello,
> I attach animated gif showing the effect. The while loop in following
> code makes whole script fast:
>
> loop=1
> while (( loop -- )); do
>     filename="lsoflsof" # 89k elements
>     body=( "${(@f)"$(<"$filename" )"}" )
> done
>
> Commenting out the loop and leaving only its body makes the whole script slow:
>
> loop=1
> #while (( loop -- )); do
>     filename="lsoflsof" # 89k elements
>     body=( "${(@f)"$(<"$filename" )"}" )
> #done
>
> This is reveals on Zsh 5.0.8 (OS X). On 5.2 it isn't visible or
> doesn't actually occur – because of recent optimizations.
>
> I wasn't able to reproduce this in some short script, but might yet
> try to do this. I'm reporting because maybe there is something hidden
> behind this.
>
> Best regards,
> Sebastian Gniazdowski

Re: Single-run while makes script fast

[Bart Schaefer]

On Dec 4,  5:20pm, Sebastian Gniazdowski wrote:
} 
} I attach animated gif showing the effect. The while loop in following
} code makes whole script fast:

By code examination rather than actual experiment --

The difference when the while-loop is introduced is that the entire
heap allocated by body=(...) is discarded with a single popheap() at
the "done", whereas without the loop the space is reclaimed by a call
to freeheap() which has to examine every heap arena.

You should be able to get the same effect with "repeat 1" so as not
to need the loop-counter variable.

This might indicate that the exec*() routines in Src/loop.c are not
doing as much as they could to keep memory footprint to its minimum.

Re: Single-run while makes script fast

[Peter Stephenson]

On Fri, 04 Dec 2015 09:43:31 -0800
Bart Schaefer <schaefer@brasslantern.com> wrote:
> This might indicate that the exec*() routines in Src/loop.c are not
> doing as much as they could to keep memory footprint to its minimum.

You might have thought there ought to be some heap arrangement around
execlist() and/or execpline().

pws

Re: Single-run while makes script fast

[Sebastian Gniazdowski]

On 4 December 2015 at 18:43, Bart Schaefer <schaefer@brasslantern.com> wrote:
> You should be able to get the same effect with "repeat 1" so as not
> to need the loop-counter variable.

Thanks for the tip, checked – repeat 1 has the same benefits

Best regards,
Sebastian Gniazdowski