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

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Message-ID: <20130821072122.GA27360@gmail.com>
Date:	Wed, 21 Aug 2013 09:21:23 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Mike Snitzer <snitzer@...hat.com>
Cc:	Stanislaw Gruszka <sgruszka@...hat.com>, dm-devel@...hat.com,
	linux-kernel@...r.kernel.org,
	Mikulas Patocka <mpatocka@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"Alasdair G. Kergon" <agk@...hat.com>
Subject: Re: [PATCH 1/2] Revert "Revert "math64: New div64_u64_rem helper""


* Mike Snitzer <snitzer@...hat.com> wrote:

> On Tue, Aug 20 2013 at  4:09am -0400,
> Ingo Molnar <mingo@...nel.org> wrote:
> 
> > 
> > * 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 for the feedback.
> 
> I've pushed "math64: New separate div64_u64_rem helper" to the DM tree's
> 'for-next' branch:
> https://git.kernel.org/cgit/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=for-next&id=20e8125736d0e96b64c9b6127241d2a13529180a
> 
> Are you OK with me carrying this patch in the DM tree for 3.12
> inclusion?

Would be nice to include the actual latest patch here on 
lkml.

Thanks,

	Ingo
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