Re: [PATCH 4/5] dts: add `show port info` command to TestPmdShell

[Luca Vizzarro <Luca.Vizzarro@arm.com>]

On 17/04/2024 15:25, Luca Vizzarro wrote:
> On 17/04/2024 14:22, Juraj Linkeš wrote:
>>> I'll
>>> experiment with some look ahead constructs. The easiest solution is to
>>> match everything that is not * ([^*]+) but can we be certain that there
>>> won't be any asterisk in the actual information?
>>
>> We can't. But we can be reasonably certain there won't be five
>> consecutive asterisks, so maybe we can work with that.
> 
> We can work with that by using look ahead constructs as mentioned, which 
> can be quite intensive. For example:
> 
>    /(?<=\n\*).*?(?=\n\*|$)/gs
> 
> looks for the start delimiter and for the start of the next block or the 
> end. This works perfectly! But it's performing 9576 steps (!) for just 
> two ports. The current solution only takes 10 steps in total.

Thinking of it... we are not really aiming for performance, so I guess 
if it simplifies and it's justifiable, then it's not a problem. 
Especially since this command shouldn't be called continuosly.

The equivalent /\n\*.+?(?=\n\*|$)/gs (but slightly more optimised) takes 
approximately 3*input_length steps to run (according to regex101 at 
least). If that's reasonable enough, I can do this:

   iter = re.finditer(input, "\n\*.+?(?=\n\*|$)", re.S)
   return [TestPmdPortInfo.parse(match.group(0)) for match in iter]

Another optimization is artificially adding a `\n*` delimiter at the end 
before feeding it to the regex, thus removing the alternative case (|$), 
and making it 2*len steps:

   input += "\n*"
   iter = re.finditer(input, "\n\*.+?(?=\n\*)", re.S)
   return [TestPmdPortInfo.parse(match.group(0)) for match in iter]

Let me know what you think!

Best,
Luca