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

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Date:	Tue, 20 Aug 2013 09:00:46 +0200
From:	Stanislaw Gruszka <sgruszka@...hat.com>
To:	Mike Snitzer <snitzer@...hat.com>
Cc:	dm-devel@...hat.com, linux-kernel@...r.kernel.org,
	Mikulas Patocka <mpatocka@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH 1/2] Revert "Revert "math64: New div64_u64_rem helper""

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;

Stanislaw

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