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

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Message-ID: <20160128092959.GA2571@codeblueprint.co.uk>
Date:	Thu, 28 Jan 2016 09:29:59 +0000
From:	Matt Fleming <matt@...eblueprint.co.uk>
To:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:	"Elliott, Robert (Persistent Memory)" <elliott@....com>,
	Andy Shevchenko <andy.shevchenko@...il.com>,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	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 Tue, 26 Jan, at 01:59:26PM, Andy Shevchenko wrote:
> On Tue, 2016-01-26 at 11:50 +0000, Matt Fleming wrote:
> > On Mon, 25 Jan, at 08:37:58PM, Elliott, Robert (Persistent Memory)
> > wrote:
> > > 
> > > For the UEFI memory map, that was indeed my intention.  I
> > > don't want it silently round to "20 GiB".  Even rounding
> > > to "19.999 GiB" is imprecise.
> > 
> > OK, let's just go with your original patch Robert (minus the @ addr
> > bit) since it's pretty small and does what we want for this specific
> > case.
> 
> However I am against this, but seems reviewers do not leave a chance to
> us, I would propose to copy-and-paste table of binary prefixes and use
> __ffs64().

Is there a benefit to this approach other than __ffs64() being faster?
It is a neglibible performance gain anyway because this is hidden
behind efi=debug, and so by definition you're not looking for ultra
performance.

Which makes picking between __ffs64() and non-__ffs64() a wash if
we're not going to be reusing existing code.