linux-kernel - Re: [PATCH v3 3/4] x86/efi: print size in binary units in efi_print

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Message-ID: <CAHp75VdYRzC9TcDpKxq=xddA0zgVk=5_25uXaimn1tOMZVeK4Q@mail.gmail.com>
Date:	Mon, 25 Jan 2016 21:28:37 +0200
From:	Andy Shevchenko <andy.shevchenko@...il.com>
To:	James Bottomley <James.Bottomley@...senpartnership.com>
Cc:	"Elliott, Robert (Persistent Memory)" <elliott@....com>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Matt Fleming <matt@...eblueprint.co.uk>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H . Peter Anvin" <hpa@...or.com>,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel @ vger . kernel . org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 3/4] x86/efi: print size in binary units in efi_print_memmap

On Mon, Jan 25, 2016 at 8:56 PM, James Bottomley
<James.Bottomley@...senpartnership.com> wrote:
> On Mon, 2016-01-25 at 18:02 +0000, Elliott, Robert (Persistent Memory)
> wrote:

>  Using ffs leads to precision runaway

How exactly?!

> and
> exporting an array from string_helpers.c is simply the wrong way to do
> it.

This part I didn't object.

> Since we've now spent more time arguing about this than it would take
> to do a correct patch, this is what I was thinking.  It extracts the
> precision reduction core from string_helpers.c and exposes it to all
> users who want to convert to units.  I added a nozeros option becuase I
> think you want it to print 1 GiB rather than 1.00 GiB for exact powers
> of two.  (OK, and I fixed a bug where it will report small amounts as
> 1.00 B instead of whole number of bytes).  Absent the nozero option,
> you could simply have used string_get_size(), with a block size of 1.

It's good you are doing this better, but I still vote for __ffs64(),
since it would be faster on binary units.

Also, in one version I tried to convert couple of other users which
are using only KM (in general whatever range it would be) units. Any
ideas how to modify to support them?

-- 
With Best Regards,
Andy Shevchenko