From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andy Shevchenko Subject: Re: [PATCH v12 01/11] bitops: Introduce the for_each_set_clump8 macro Date: Tue, 26 Mar 2019 13:42:52 +0200 Message-ID: <20190326114252.GX9224@smile.fi.intel.com> References: <9afc30a574ce3e6a86b51dd522146a1d2156dedd.1553494625.git.vilhelm.gray@gmail.com> <20190325131236.GW9224@smile.fi.intel.com> <20190326025459.GA3356@icarus> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20190326025459.GA3356@icarus> Sender: linux-kernel-owner@vger.kernel.org To: William Breathitt Gray Cc: linus.walleij@linaro.org, bgolaszewski@baylibre.com, akpm@linux-foundation.org, linux-gpio@vger.kernel.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, linux@rasmusvillemoes.dk, yamada.masahiro@socionext.com, linux-arm-kernel@lists.infradead.org, linux-pm@vger.kernel.org, geert@linux-m68k.org, preid@electromag.com.au, Arnd Bergmann List-Id: linux-gpio@vger.kernel.org On Tue, Mar 26, 2019 at 11:54:59AM +0900, William Breathitt Gray wrote: > On Mon, Mar 25, 2019 at 03:12:36PM +0200, Andy Shevchenko wrote: > > On Mon, Mar 25, 2019 at 03:22:23PM +0900, William Breathitt Gray wrote: > > > This macro iterates for each 8-bit group of bits (clump) with set bits, > > > within a bitmap memory region. For each iteration, "start" is set to the > > > bit offset of the found clump, while the respective clump value is > > > stored to the location pointed by "clump". Additionally, the > > > bitmap_get_value8 and bitmap_set_value8 functions are introduced to > > > respectively get and set an 8-bit value in a bitmap memory region. > > > > > > This seems to miss Randy's (IIRC) comment about too many const specifiers. > > I disagree with removing the const qualifiers; I believe they are useful > and do not significantly impact the clarity of the code (in fact, I'd > argue the opposite). Had you checked the assembly? I'm talking about const for values on the stack. I think if you put less const there compiler can keep something in the registers instead of using direct constants or accessing stack. I might be mistaken, so, I can't argue without evidence of either. > The const qualifiers make it clear these values are > constant, allowing readers at a glace to know these values never change > within this function. Although I believe GCC is smart enough in this > case to deduce implicitly that these are constant values, generally > speaking const qualifiers do make it easier for compilers to optimize > sections of code (OoO execution, algorithm simplification, etc.), so I > believe it's useful in a technical sense as well. Again, what the difference do you see in assembly if any? > I added the const qualifier to these variables because they really are > constant, and I believe there is merit in making it explicit in the > code. If the primary reason for removing the const qualifiers is for > aesthetics, then I must dissent with that decision. The point is, if there is no difference, I would prefer one which will be better to read, otherwise check the assembly. > However, it is difficult to read the definitions that wrap around to a > second line. These definitions are long enough that even removing the > const qualifiers would not help prevent the wrapping, so perhaps it > would make to let these stay on a single line. Do you think it would > help to ignore the 80-character maximum line width coding style rule for > these cases here? 80-characters rule can be slightly bended depending on the context. Here, I think, we might continue discussing the matter after having an evidence how const qualifiers affect the code. -- With Best Regards, Andy Shevchenko