linux-kernel - Re: [PATCH v3 1/5] lib/bitmap: add bitmap_{set,get}

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Date:   Mon, 17 Jul 2023 17:29:12 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     unlisted-recipients:; (no To-header on input)
Cc:     catalin.marinas@....com, will@...nel.org, pcc@...gle.com,
        andreyknvl@...il.com, linux@...musvillemoes.dk,
        yury.norov@...il.com, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, eugenis@...gle.com,
        syednwaris@...il.com, william.gray@...aro.org,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v3 1/5] lib/bitmap: add bitmap_{set,get}_value()

On Mon, Jul 17, 2023 at 04:14:57PM +0200, Alexander Potapenko wrote:

+Cc: Nathan (on code generation question below)

...

> > > Cc: Arnd Bergmann <arnd@...db.de>
> >
> > You can use --cc to `git send-email` instead of polluting the commit message.
> 
> Right. But as far as I can tell, certain kernel devs prefer to be CCed
> on the whole series, whereas others do not want to see anything but
> the actual patch they were interested in.
> I am not sure about Arnd's preferences, so I just decided to keep the
> tag from the original patch by Syed Nayyar Waris (which I also
> consider to be an indication of the fact "that potentially interested
> parties have been included in the discussion" per
> https://www.kernel.org/doc/html/v4.17/process/submitting-patches.html#when-to-use-acked-by-cc-and-co-developed-by)

My personal statistics from the field that more than 90% of maintainers would
like to receive 100% of the series. Of course it depends on the series (if it's
treewide, I will agree with you). Here another point to my suggestion is that
Arnd is SoC tree maintainer, where ARM is one of the biggest player, so I think
he would like to see arm*: prefixed patches anyway.

...

> > > +             map[index] &= ~(GENMASK(nbits + offset - 1, offset));
> >
> > I remember that this construction may bring horrible code on some architectures
> > with some version(s) of the compiler (*).
> 
> Wow, even the trunk Clang and GCC seem to generate better code for
> your version of this line: https://godbolt.org/z/36Kqxhe6j

Wow, indeed! Perhaps time to report to clang and GCC people. I believe the root
cause is that in the original version compiler can't prove that l is constant
for GENMASK().

> > To fix that I found an easy refactoring:
> >
> >                 map[index] &= ~(GENMASK(nbits, 0) << offset));
> 
> I'll take this one.
> 
> > (*) don't remember the actual versions, though, but anyway...

-- 
With Best Regards,
Andy Shevchenko