linux-kernel - Re: [PATCH v1 1/1] bitops: Share BYTES_TO

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Message-ID: <ZP3NlPOGtbT7CGQ1@yury-ThinkPad>
Date:   Sun, 10 Sep 2023 07:07:16 -0700
From:   Yury Norov <yury.norov@...il.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Alexander Lobakin <aleksander.lobakin@...el.com>,
        Uros Bizjak <ubizjak@...il.com>,
        "Masami Hiramatsu (Google)" <mhiramat@...nel.org>,
        linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH v1 1/1] bitops: Share BYTES_TO_BITS() for everyone

On Wed, Sep 06, 2023 at 05:54:26PM +0300, Andy Shevchenko wrote:
> On Wed, Sep 06, 2023 at 04:40:39PM +0200, Alexander Lobakin wrote:
> > From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> > Date: Thu, 31 Aug 2023 16:21:30 +0300
> > > On Fri, Aug 25, 2023 at 04:49:07PM +0200, Alexander Lobakin wrote:
> > >> From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> > >> Date: Thu, 24 Aug 2023 15:37:28 +0300
> > >>
> > >>> It may be new callers for the same macro, share it.
> > >>>
> > >>> Note, it's unknown why it's represented in the current form instead of
> > >>> simple multiplication and commit 1ff511e35ed8 ("tracing/kprobes: Add
> > >>> bitfield type") doesn't explain that neither. Let leave it as is and
> > >>> we may improve it in the future.
> > >>
> > >> Maybe symmetrical change in tools/ like I did[0] an aeon ago?
> > > 
> > > Hmm... Why can't you simply upstream your version? It seems better than mine.
> > 
> > It was a part of the Netlink bigint API which is a bit on hold for now
> > (I needed this macro available treewide).
> > But I can send it as standalone if you're fine with that.
> 
> I'm fine. Yury?

Do we have opencoded BYTES_TO_BITS() somewhere else? If so, it should be
fixed in the same series.

Regarding implementation, the current:

        #define BYTES_TO_BITS(nb)      ((BITS_PER_LONG * (nb)) / sizeof(long))

looks weird. Maybe there are some special considerations in a tracing
subsystem to make it like this, but as per Masami's email - there's
not. 

For a general purpose I'd suggest a simpler:
        #define BYTES_TO_BITS(nb)      ((nb) * BITS_PER_BYTE)

Thanks,
Yury