RegExp performance

Michael Daumling mdaeumli at adobe.com
Tue Jun 24 07:59:18 PDT 2008


Hi Lars,

Well spoken!

_pcre_exec uses the heap to allocate recursion information. There is a
#define NO_RECURSE in config.h. When I comment out this #define, pcre
apparently uses the stack, and no memory allocation takes place at all.
The change causes the ecma3/unicode tests to run significantly faster -
from 1:15 min to 56 secs.

What do the platform experts say? Can we compile pcre without NO_RECURSE
on some platforms?

Michael
 

-----Original Message-----
From: Lars Hansen 
Sent: Tuesday, June 24, 2008 7:50 AM
To: Michael Daumling; tamarin-devel at mozilla.org
Subject: RE: RegExp performance

It would be interesting to know why that allocation is going on.  RE
execution should need to allocate for suspended decision points and for
capture arrays, but I would have hoped the engine had optimized those
significantly to avoid hitting the allocator all the time.  What do the
test cases look like, and why do they tickle such an allocation volume?

--lars

> -----Original Message-----
> From: tamarin-devel-bounces at mozilla.org [mailto:tamarin-devel- 
> bounces at mozilla.org] On Behalf Of Michael Daumling
> Sent: 24. juni 2008 16:43
> To: tamarin-devel at mozilla.org
> Subject: RegExp performance
> 
> Hi all,
> 
> I have used GlowCode (yet another profiling tool that you can test for
> 21 days) to examine RegExp performance in TT.
> 
> The big surprise was that _pcre_exec does a *lot* of mallocs and free 
> (plus a ton of setjmp/longjmp). The difference between TC and TT is 
> that TC has a global override of operators new and delete (in 
> AvmShell.cpp) that uses FixedMalloc::Alloc/Free, and TT uses malloc 
> and free via the default global new and delete operators.
> 
> Switching the pcre allocators (in pcre_globals.cpp amd 
> RegExpClass.cpp) to using FixedMalloc showed a very nice improvement, 
> but only in GlowCode. In the real world, the ecma3/Unicode tests were
slower!
> 
> I am out of knowledge here. Is it possible that 
> FixedMalloc::Alloc/Free is slower in TT than in TC? Should I have 
> tried a different (fast) replacement for malloc/free? Was the usage of

> malloc/free intentional at all?
> 
> BTW: String handling (UTF-8 conversion etc) is negligible in that 
> context. The big hog is malloc/free from within _pcre_exec (about 60% 
> of total time).
> 
> Michael
> 
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