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

[Jonathan Corbet <corbet@lwn.net>]

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

> Hmm... I opted for this particular way of checking is that I
> expect that check inside a hash at dict would be faster than
> letting it crash then raise an exception. 

Raising an exception is not quite a "crash" and, if the caching is doing
any good, it should be ... exceptional.  That pattern is often shown as
a better way to do conditional dict lookups, so I've tended to follow
it, even though I'm not a big fan of exceptions in general.

> Btw, one easy way to check how much it affects performance
> (if any) would be to run it in "rogue" mode with:
>
> 	$ time ./scripts/kernel-doc.py -N .
>
> This will run kernel-doc.py for all files at the entire Kernel
> tree, only reporting problems. If you want to do changes like
> this that might introduce performance regressions, I suggest
> running it once, just to fill disk caches, and then run it
> again before/after such changes.
>
> Anyway, I did such measurements before/after your patch.
> the difference was not relevant: just one second of difference:
>
> original code:
>
> real	1m20,839s
> user	1m19,594s
> sys	0m0,998s
>
> after your change:
>
> real	1m21,805s
> user	1m20,612s
> sys	0m0,929s
>
> I don't mind myself to be one second slower, but this is hardly
> a micro-optimization ;-)

Docs builds generally went slightly faster for me, but that is always a
noisy signal.

Anyway, I am not tied to this patch and can drop it.  Or I suppose I
could just redo it with .get(), which avoids both the double lookup and
the exception.

Thanks,

jon