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

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Date:   Wed, 30 Aug 2023 16:16:00 +0900
From:   Masami Hiramatsu (Google) <mhiramat@...nel.org>
To:     Alexander Lobakin <aleksander.lobakin@...el.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Yury Norov <yury.norov@...il.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 Fri, 25 Aug 2023 16:49:07 +0200
Alexander Lobakin <aleksander.lobakin@...el.com> 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?

Hm, it looks the same. The reason why I used the macro was I didn't
know the BITS_PER_TYPE() at that point. Now it is OK to replace it
with 'bytes * BITS_PER_TYPE(char)'.

Thank you,

> 
> > 
> > Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> > ---
> >  include/linux/bitops.h     | 2 ++
> >  kernel/trace/trace_probe.c | 3 +--
> >  2 files changed, 3 insertions(+), 2 deletions(-)
> > 
> > diff --git a/include/linux/bitops.h b/include/linux/bitops.h
> > index 2ba557e067fe..66dc091e0c28 100644
> > --- a/include/linux/bitops.h
> > +++ b/include/linux/bitops.h
> > @@ -21,6 +21,8 @@
> >  #define BITS_TO_U32(nr)		__KERNEL_DIV_ROUND_UP(nr, BITS_PER_TYPE(u32))
> >  #define BITS_TO_BYTES(nr)	__KERNEL_DIV_ROUND_UP(nr, BITS_PER_TYPE(char))
> >  
> > +#define BYTES_TO_BITS(nb)	((BITS_PER_LONG * (nb)) / sizeof(long))
> > +
> >  extern unsigned int __sw_hweight8(unsigned int w);
> >  extern unsigned int __sw_hweight16(unsigned int w);
> >  extern unsigned int __sw_hweight32(unsigned int w);
> > diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
> > index c68a72707852..da6297d24d61 100644
> > --- a/kernel/trace/trace_probe.c
> > +++ b/kernel/trace/trace_probe.c
> > @@ -11,6 +11,7 @@
> >   */
> >  #define pr_fmt(fmt)	"trace_probe: " fmt
> >  
> > +#include <linux/bitops.h>
> >  #include <linux/bpf.h>
> >  
> >  #include "trace_probe.h"
> > @@ -830,8 +831,6 @@ parse_probe_arg(char *arg, const struct fetch_type *type,
> >  	return ret;
> >  }
> >  
> > -#define BYTES_TO_BITS(nb)	((BITS_PER_LONG * (nb)) / sizeof(long))
> > -
> >  /* Bitfield type needs to be parsed into a fetch function */
> >  static int __parse_bitfield_probe_arg(const char *bf,
> >  				      const struct fetch_type *t,
> 
> [0]
> https://github.com/alobakin/linux/commit/fd308001fe6d38837fe820427209a6a99e4850a8
> 
> Thanks,
> Olek


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>