Re: [PATCH v2 2/7] docs: kdoc: micro-optimize KernRe

[Jonathan Corbet <corbet@lwn.net>]

Mauro Carvalho Chehab <mchehab+huawei@kernel.org> writes:

> Em Thu, 03 Jul 2025 17:47:13 -0600
> Jonathan Corbet <corbet@lwn.net> escreveu:
>
>> Mauro Carvalho Chehab <mchehab+huawei@kernel.org> writes:
>> 
>> > Em Thu,  3 Jul 2025 12:43:58 -0600
>> > Jonathan Corbet <corbet@lwn.net> escreveu:
>> >  
>> >> Rework _add_regex() to avoid doing the lookup twice for the (hopefully
>> >> common) cache-hit case.
>> >> 
>> >> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
>> >> ---
>> >>  scripts/lib/kdoc/kdoc_re.py | 7 ++-----
>> >>  1 file changed, 2 insertions(+), 5 deletions(-)
>> >> 
>> >> diff --git a/scripts/lib/kdoc/kdoc_re.py b/scripts/lib/kdoc/kdoc_re.py
>> >> index e81695b273bf..612223e1e723 100644
>> >> --- a/scripts/lib/kdoc/kdoc_re.py
>> >> +++ b/scripts/lib/kdoc/kdoc_re.py
>> >> @@ -29,12 +29,9 @@ class KernRe:
>> >>          """
>> >>          Adds a new regex or re-use it from the cache.
>> >>          """
>> >> -
>> >> -        if string in re_cache:
>> >> -            self.regex = re_cache[string]
>> >> -        else:
>> >> +        self.regex = re_cache.get(string, None)  
>> >
>> > With get, None is default...
>> >  
>> >> +        if not self.regex:
>> >>              self.regex = re.compile(string, flags=flags)  
>> >
>> > ... yet, as you're using get, better to code it as:
>> >
>> > 	self.regex = re_cache.get(string, re.compile(string, flags=flags))  
>> 
>> ...but that will recompile the regex each time, defeating the purpose of
>> the cache, no?
>
> No. It should do exactly like the previous code:
>
> - if re_cache[string] exists, it returns it. 
> - Otherwise, it returns re.compile(string, flags=flags).
>
> https://www.w3schools.com/python/ref_dictionary_get.asp

The re.compile() call is evaluated before the call to get() - just like
it would be in C.  This is easy enough to prove to yourself in the REPL
if you doubt me...

Thanks,

jon