[poppler] Small perf improvement to bug 11849

[Krzysztof Kowalczyk]

The code is really trivial: a 4 element stack, in delete objects are
pushed on stack (if there's space), in new objects are popped from
stack.

What's brainded about overloading new/delete?

After some thinking I think overloading is better because it has one
big advantage: it requires no changes to poppler code (other than
adding some more code).

In that it makes merges with xpdf easier.

Without overloading you need to replace every new/delete SplashPath
with SplashPath::create/SplashPath::destroy, which results in more
changes.

-- kjk

On 9/26/07, Albert Astals Cid <aacid at kde.org> wrote:
> A Dimecres 26 Setembre 2007, Krzysztof Kowalczyk va escriure:
> > So I started looking at perf again.
> >
> > The first improvement is ~4% rendering speedup for PDF in
> > https://bugs.freedesktop.org/show_bug.cgi?id=11849.
> >
> > From the profile it looked like in this case a great deal (129899) of
> > SplashPath objects was created/destroyed, yet at any given time only a
> > few were allocated at the same time, so a small cache to recycle
> > objects improves that. With this PDF I get the following changes for
> > alloc functions counts:
> >
> > before:
> > gfree  0.31   0.31    100.00  1092627
> > gmalloc        0.18   0.18    100.00  548663
> > grealloc 0.13 0.13    100.00  389808
> >
> > after:
> > gfree 0.16    0.16    100.00  702930
> > gmalloc       0.14    0.14    100.00  548663
> > grealloc0.03  0.03    100.00  98382
> >
> > I measure speed up with the newly added test/perf-test, using release
> > build on windows, like this:
> > perftest.exe -timings c:\kjk\downloads\slow00.pdf
> >
> > For comparison I take the smallest number out of few runs.
> >
> > You'll see the code when I solve my branch pushing troubles.
> >
> > There are some issues:
> > * this applies to all caches: cache must be emptied at some point,
> > especially at the end, in order to not be seen as a leak. But poppler
> > doesn't have mandatory init/free function to stuff it. So for now the
> > user of the library needs to know. I was thinking it could be added
> > either in PDFDoc destructor (based on assumption that we only want the
> > cache to live as long as the document, because it really only improves
> > a small class of PDFs) or in GlobalParams, since it must be
> > constructed/destructed
> > * right now a static function SplashFont::create()/destroy() must be
> > called instead of new/delete SplashFont but I think it could be done
> > transparently by substituting new/delete for this class. Need to dust
> > up those C++ books.
>
> I'm very hesitant on the amount of complex code that can introduce just to win
> a 4% on some specific pdf, but we'll see once your branch is online for
> testing.
>
> And also please, don't overload the new operator, imho that's braindead and
> using SplashFont::create()/destroy() is just OK. new gives you the "normal"
> behvaiour and create()/destroy() the cached one, that makes sense.
>
> Albert
>
> > Also this approach could be used for a few other classes:
> > SplashXPath                 47889    4        48      0       0       574668
> > GfxPath                              42970    2       80      0       0       1718800
> > SplashXPathScanner     42074    4     208     0       0       2187848
> > SplashSolidColor           38410   20 160     0       0       307280
> >
> > First number is total number of created objects during rendering this
> > PDF, second is max number of objects existing at the same time. Second
> > number is important for deciding cache size. If it's 4, cache of size
> > 4 should provide almost 100% hit ratio (i.e. almost all allocations
> > should be satisfied from the cache).
> >
> > -- kjk
> > _______________________________________________
> > poppler mailing list
> > poppler at lists.freedesktop.org
> > http://lists.freedesktop.org/mailman/listinfo/poppler
>
>
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