Re: [xslt] likely/unlikely hinting for libxml/libxslt

[Stefan Kost <ensonic hora-obscura de>]

Am 15.02.2010 10:47, schrieb Stefan Behnel:
> 
> Stefan Kost, 10.02.2010 09:43:
>> in the quest of figuring our what canb be done to make gtk-doc less slow
>> (where the only slow part is the docbook xslt processing) I was running
>> it under oprofile and studying the report. Below is the profile
>> (probably nothing new in there). Attached is also the callgraph as an
>> image (not sure if that will get through to the list).
> 
> Note that KCacheGrind claims to have support for oprofile. Should make such
> a graph a lot more accessible.
> 
> 
>> Some questions:
>>
>> * I'd suggest to make use of __builtin_expect() in libxml. glib does:
>>
>> #if defined(__GNUC__) && (__GNUC__ > 2) && defined(__OPTIMIZE__)
>> #define G_LIKELY(expr) (__builtin_expect ((expr), 1))
>> #define G_UNLIKELY(expr) (__builtin_expect ((expr), 0))
>> #else
>> #define G_LIKELY(expr) (expr)
>> #define G_UNLIKELY(expr) (expr)
>> #endif
> 
> We actually do this in Cython:
> 
> #ifdef __GNUC__
> /* Test for GCC > 2.95 */
> #if __GNUC__ > 2 || \
>               (__GNUC__ == 2 && (__GNUC_MINOR__ > 95))
> #define likely(x)   __builtin_expect(!!(x), 1)
> #define unlikely(x) __builtin_expect(!!(x), 0)
> #else /* __GNUC__ > 2 ... */
> #define likely(x)   (x)
> #define unlikely(x) (x)
> #endif /* __GNUC__ > 2 ... */
> #else /* __GNUC__ */
> #define likely(x)   (x)
> #define unlikely(x) (x)
> #endif /* __GNUC__ */
> 
> 
>> Could that be added to libxml as e.g. XML_{UN,}LIKELY?
> 
> +1
> 
>> It could be used e.g. in xpathInternals.h, e.g. for
>>
>> #define CHECK_ERROR                            \
>>     if (XML_UNLIKELY (ctxt->error != XPATH_EXPRESSION_OK)) return
>>
>> With the attached (hackish patch) I got the % for xmlXPathCompOpEval
>> from 22.69% down to 17.70%.
>> (this was just on, but one long iteration).
> 
> Sounds like a case to me.
> 
> 
>> If there is no one against such an approach I can make a proper patch
>> and submit it to bugzilla.
> 
> Please do. I can't guarantee that it will go in, but once it's there, I
> can't really see a reason why it shouldn't.

Sorry, I missed the reply. I have the patch now, but I must have had a
meassurement error paired with sudden euphoria of being able to to speed things
up. I havn't got a convincing speedup since. I'll need to run more tests and
exclude external interference.

Stefan

> 
> Stefan
> 
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