linux-kernel - Re: [PATCH 07/29] x86/boot/e820: Print out sizes of E820 memory ranges

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Message-ID: <aCcCFZtk9LWFQpf5@smile.fi.intel.com>
Date: Fri, 16 May 2025 12:15:01 +0300
From: Andy Shevchenko <andy.shevchenko@...il.com>
To: Ingo Molnar <mingo@...nel.org>
Cc: linux-kernel@...r.kernel.org, Arnd Bergmann <arnd@...nel.org>,
	Borislav Petkov <bp@...en8.de>, Juergen Gross <jgross@...e.com>,
	"H . Peter Anvin" <hpa@...or.com>,
	Kees Cook <keescook@...omium.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Mike Rapoport <rppt@...nel.org>,
	Paul Menzel <pmenzel@...gen.mpg.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	David Woodhouse <dwmw@...zon.co.uk>
Subject: Re: [PATCH 07/29] x86/boot/e820: Print out sizes of E820 memory
 ranges

On Thu, May 15, 2025 at 12:44:06PM +0200, Ingo Molnar wrote:
> * Andy Shevchenko <andy.shevchenko@...il.com> wrote:
> > Mon, Apr 21, 2025 at 08:51:47PM +0200, Ingo Molnar kirjoitti:

...

> > > +	if (size & (SZ_1T-1))
> > > +		pr_cont(" %4llu.%01llu TB", size/SZ_1T, 10*(size & (SZ_1T-1))/SZ_1T);
> > > +	else
> > > +		pr_cont(" %4llu   TB", size/SZ_1T);
> > > +}
> > 
> > Don't you want to use string_helpers.h provided API? 
> > string_get_size().
> 
> I don't think string_get_size() knows the fine distinction between:
> 
>     BIOS-e820: [mem 0x00000000fffc0000-0x00000000ffffffff]  256   KB device reserved
> 
> and:
> 
>     BIOS-e820: [mem 0x00000000fffc0000-0x00000000ffffffff]  256.0 KB device reserved
> 
> "256 KB" is exactly 256 KB, while "256.0 KB" denotes a value that is a 
> bit larger than 256 KB but rounds down to 256 KB at 1 KB granularity.
> 
> When reading platform boot logs it's useful to know when such values 
> are exact, at a glance.

We can patch string_size() to print precise integers without fractional part.

-- 
With Best Regards,
Andy Shevchenko