linux-kernel - Re: [PATCH 1/2] Revert "Revert "math64: New div64_u64

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Message-ID: <20130820080910.GA11072@gmail.com>
Date:	Tue, 20 Aug 2013 10:09:10 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Stanislaw Gruszka <sgruszka@...hat.com>
Cc:	Mike Snitzer <snitzer@...hat.com>, dm-devel@...hat.com,
	linux-kernel@...r.kernel.org,
	Mikulas Patocka <mpatocka@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH 1/2] Revert "Revert "math64: New div64_u64_rem helper""


* Stanislaw Gruszka <sgruszka@...hat.com> wrote:

> On Fri, Aug 09, 2013 at 03:56:03PM -0400, Mike Snitzer wrote:
> > This reverts commit f3002134158092178be81339ec5a22ff80e6c308.
> > 
> > div64_u64_rem was removed because there were no other users.
> > 
> > But Device Mapper's I/O statistics support has a need for
> > div64_u64_rem; reintroduce this helper.
> 
> This slows down div64_u64 operation, especially on 32-bit 
> systems.
> 
> Since dm statistic code is possibly not performance 
> critical perhaps you could use something like below 
> instead to calculate remainder:
> 
> res = div64_u64(a, b);
> rem = a - b*res;

Or introduce a separately named helper without touching the 
existing methods.

Thanks,

	Ingo
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