linux-kernel - Re: [PATCH v2] Btrfs: use do_div to avoid compile errors on 32bit box

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Date:	Sat, 20 Aug 2011 18:04:51 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Josef Bacik <josef@...hat.com>
Cc:	Liu Bo <liubo2009@...fujitsu.com>, linux-kernel@...r.kernel.org,
	mingo@...nel.org, jwboyer@...il.com, linux-btrfs@...r.kernel.org,
	chris.mason@...cle.com, dave@...os.cz
Subject: Re: [PATCH v2] Btrfs: use do_div to avoid compile errors on 32bit box

On Sat, Aug 20, 2011 at 5:21 AM, Josef Bacik <josef@...hat.com> wrote:
>
> I think Linus was less complaining about how you're dividing here and
> more about the fact that you are.  A divide by 2 is the same as a >> 1.
>  I'll send a patch to fix this.  Thanks,

Indeed. A single-bit 64-bit "double shift" may be a few cycles, but
it's still pretty damn cheap. Especially when compared to a 64x32 bit
divide. We absolutely don't want to do "do_div()" in order to divide
by the constant 2.

                     Linus
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