linux-kernel - Re: [PATCH v4 14/14] of: Improve __of_add_property

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Message-ID: <qvyhzgeye7qwppcafisvjkg4wwkrenwxq7nebnsjxdenj7wvxm@qwxzet3iyzyx>
Date: Sat, 11 Jan 2025 10:17:25 +0100
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Zijun Hu <zijun_hu@...oud.com>
Cc: Rob Herring <robh@...nel.org>, Saravana Kannan <saravanak@...gle.com>, 
	Maxime Ripard <mripard@...nel.org>, Robin Murphy <robin.murphy@....com>, 
	Grant Likely <grant.likely@...retlab.ca>, Marc Zyngier <maz@...nel.org>, 
	Andreas Herrmann <andreas.herrmann@...xeda.com>, Marek Szyprowski <m.szyprowski@...sung.com>, 
	Catalin Marinas <catalin.marinas@....com>, Mike Rapoport <rppt@...nel.org>, 
	Oreoluwa Babatunde <quic_obabatun@...cinc.com>, devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Zijun Hu <quic_zijuhu@...cinc.com>
Subject: Re: [PATCH v4 14/14] of: Improve __of_add_property_sysfs()
 readability

On Sat, Jan 11, 2025 at 07:48:48AM +0800, Zijun Hu wrote:
> On 2025/1/11 04:41, Rob Herring wrote:
> > On Thu, Jan 09, 2025 at 09:27:05PM +0800, Zijun Hu wrote:
> >> From: Zijun Hu <quic_zijuhu@...cinc.com>
> >>
> >> __of_add_property_sysfs() hard codes string "security-" length as 9, but
> >> that is not obvious for readers.
> >>
> >> Improve its readability by using strlen().
> > 
> > Does the compiler optimize the strlen call away? Maybe, maybe not. If 
> > not, that's N calls to strlen() where N is the number of properties in 
> > your DT. That's in the 1000s easily.
> > 
> > Do you really want to go test enough compiler versions we support to 
> > feel confident this is optimized away. I don't.
> > 
> 
> i understand your concern about performance.
> perhaps, such impact about performance may be ignored for linux OS.
> 
> what about below solution ?
> 
> const char security_prefix[] = "security-";
> use 'sizeof(security_prefix) - 1' for the length of string.

Code is still not equivalent - just de-assemble it and you will see
some overhead.

Maybe just introduce builtin_strlen() to string.h and use such? It would
be the pretty obvious code.


Best regards,
Krzysztof