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Re: Performance issue of libtool-2.4.4

From: Richard Purdie
Subject: Re: Performance issue of libtool-2.4.4
Date: Tue, 10 Feb 2015 10:35:52 +0000

On Mon, 2015-02-09 at 23:36 +0000, Richard Purdie wrote:
> On Mon, 2015-02-09 at 13:05 +0000, Richard Purdie wrote:
> > In an effort to get to the bottom of this I made a git bisection, timing
> > the performance of building xz with make -j1 using each different
> > libtool.
> > 
> > The issues come down to this commit:
> > 
> >
> > 
> > libtool: rewritten over instead of general.m4sh.
> > 
> > Before that, I get a time of about 20s, after it, 39s. If I cherry-pick
> > in the fix in master mentioned above, I get 27s.
> > 
> > So whilst things are better (thanks!), the above change is still causing
> > a regression in the performance somewhere else. Any ideas what else in
> > that rather large change may be causing this?
> To further narrow this down, of the changes in the above commit, the
> problem appears to be in the changes to the option parsing code. I've
> included the diff below which if I apply on top of the above, I get the
> speed back. I've left the func_split_short_opt/func_split_long_opt code
> in there but that is worth a tiny part of the speed, the issues are
> around the addition of the func_options call.
> As yet I don't know enough about the code in question to know why this
> is an issue but traces of libtool show a lot more looping in code to do
> with argument parsing and quoting.

To be more specific, if I take my "good" libtool and add:

func_options_prep ${1+"$@"}

it slows the build down by 0.5s on a 21s build. If I look at
func_options_prep and comment out the line:

    func_run_hooks func_options_prep ${1+"$@"}

I get the 0.5s back.

In func_run_hooks, if I comment:

    func_quote_for_eval ${1+"$@"}

I get the 0.5s back. The issue is all the quoting of the various return
values through all this looping. It doesn't appear to be hitting the
printf/sed in func_quote_for_eval which would be an obvious slow path,
its just the shear number of loops run through with the commandline
arguments. The change adds a number of calls to func_run_hooks, not just
the single test case I have above and all combined, it slows things down

So is there a way we can change things so its not calling
func_quote_for_eval all the time with all the looping that entails?



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