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

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Message-ID: <CAHp75Vdc9=uotvaf4pQfRoViyWuEXhXjZH7GVWEG79AquPVi5A@mail.gmail.com>
Date:	Sat, 23 Jan 2016 19:18:18 +0200
From:	Andy Shevchenko <andy.shevchenko@...il.com>
To:	James Bottomley <James.Bottomley@...senpartnership.com>
Cc:	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,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel @ vger . kernel . org" <linux-kernel@...r.kernel.org>,
	Robert Elliott <elliott@....com>
Subject: Re: [PATCH v3 3/4] x86/efi: print size in binary units in efi_print_memmap

On Sat, Jan 23, 2016 at 6:44 PM, James Bottomley
<James.Bottomley@...senpartnership.com> wrote:
> On Sat, 2016-01-23 at 16:55 +0200, Andy Shevchenko wrote:

>> +static char * __init efi_size_format(char *buf, size_t size, u64
>> bytes)
>> +{
>> +     unsigned long i = bytes ? __ffs64(bytes) / 10 : 0;
>
> What if size is zero, which might happen on a UEFI screw up?

size of what? Of input buffer?

>  Also it
> gives really odd results for non power of two memory sizes. 16384MB
> prints as 16GiB but 16385 prints as 16385MiB.

Adaptive precision. I don't think the idea is to print a nearby numbers here.

> If the goal is to have a clean interface reporting only the first four
> significant figures and a size exponent, then a helper would be much
> better than trying to open code this ad hoc.

No. You get it wrong. The initial idea was (actually not mine, see
authorship) to print an exact number with units and reduce whenever
it's possible, i.e number is a multiplication of certain unit.

> Not an attack on you patch per-se, but I really hate the IEC convention
> that was essentially a ploy by disk manufacturers to inflate their disk
> sizes by 10% simply by relabelling them.

>  Everyone was happy when a GB was 2^30,

No, not everyone. It was a misspelling done by some first storage
producer. Try to look at the problem from physics point of view. Units
are essential part of a value. There is an agreement how to use
multipliers and their code names. 1000 x Unit means kiloUnit. As per
agreement.

> now everyone's simply confused whenever they see GB.  We had
> to pander to this in block devices because people got annoyed when we
> reported a size that was different from the label but are you sure we
> have to extend the madness to memory?

I actually don't know who is from us is being more conservative. I
could call a madness to mess things from ancient (classical
mathematics and physics) with something which has less than hundred
years in development.

-- 
With Best Regards,
Andy Shevchenko