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

Jonathan Corbet posted 7 patches 3 months ago
[PATCH v2 2/7] docs: kdoc: micro-optimize KernRe
Posted by Jonathan Corbet 3 months ago 
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)
+        if not self.regex:
             self.regex = re.compile(string, flags=flags)
-
             if self.cache:
                 re_cache[string] = self.regex
 
-- 
2.49.0
Re: [PATCH v2 2/7] docs: kdoc: micro-optimize KernRe
Posted by Mauro Carvalho Chehab 3 months ago 
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))

> -
>              if self.cache:
>                  re_cache[string] = self.regex
>  



Thanks,
Mauro
Re: [PATCH v2 2/7] docs: kdoc: micro-optimize KernRe
Posted by Jonathan Corbet 3 months ago 
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?

Thanks,

jon
Re: [PATCH v2 2/7] docs: kdoc: micro-optimize KernRe
Posted by Mauro Carvalho Chehab 3 months ago 
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


Thanks,
Mauro
Re: [PATCH v2 2/7] docs: kdoc: micro-optimize KernRe
Posted by Jonathan Corbet 3 months ago 
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
Re: [PATCH v2 2/7] docs: kdoc: micro-optimize KernRe
Posted by Mauro Carvalho Chehab 3 months ago 
Em Fri, 04 Jul 2025 08:59:45 -0600
Jonathan Corbet <corbet@lwn.net> escreveu:

> 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...

You're right!

Tested with the small code snippet:

	# test.py
	inner called
	Inner will be called: True
	inner called
	Inner should  not be called: False

I guess I expected too much from python's optimizer ;-) My fault.

Your patch looks OK to me.

Reviewed-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

-

As reference, this was the test code

#!/usr/bin/env python3

def inner():
   print("inner called")

   return True

c = {}

print(f"Inner will be called: {c.get('a', inner())}")

c = { "a": "False"}

print(f"Inner should  not be called: {c.get('a', inner())}")




Thanks,
Mauro
Re: [PATCH v2 2/7] docs: kdoc: micro-optimize KernRe
Posted by Mauro Carvalho Chehab 3 months ago 
Em Fri, 4 Jul 2025 00:31:46 +0200
Mauro Carvalho Chehab <mchehab+huawei@kernel.org> escreveu:

> 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))

For got to mention: with or without that:

Reviewed-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

> 
> > -
> >              if self.cache:
> >                  re_cache[string] = self.regex
> >  
> 
> 
> 
> Thanks,
> Mauro



Thanks,
Mauro

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