From: Jan Kara <jack@suse.cz>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Jan Kara <jack@suse.cz>, Wu Fengguang <fengguang.wu@intel.com>,
LKML <linux-kernel@vger.kernel.org>,
linux-mm@kvack.org
Subject: Re: [PATCH 1/2] lib: Proportions with flexible period
Date: Fri, 18 May 2012 16:33:15 +0200 [thread overview]
Message-ID: <20120518143315.GB6875@quack.suse.cz> (raw)
In-Reply-To: <1337290512.4281.91.camel@twins>
On Thu 17-05-12 23:35:12, Peter Zijlstra wrote:
> On Tue, 2012-05-15 at 17:43 +0200, Jan Kara wrote:
> > + if (numerator > ((long long)denominator) * max_frac / 100)
>
> Does that even compile on 32bit archs?
>
> Operator precedence is *,/ left-to-right, so that's:
>
> long long t1 = (long long)denom * max_frac
> long long t2 = t1 / 100;
>
> Which is a 64bit signed division.
>
> There's a reason I used that max_prop_frac thing you removed, it avoids
> having to do the division at all and allows a mult and shift instead.
Yeah, I misunderstood it's purpose when I read the code originally. I'll
put it back to avoid the division since this is a hot path.
Honza
--
Jan Kara <jack@suse.cz>
SUSE Labs, CR
next prev parent reply other threads:[~2012-05-18 14:33 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-05-15 15:43 [PATCH 0/2 v3] Flexible proportions Jan Kara
2012-05-15 15:43 ` [PATCH 1/2] lib: Proportions with flexible period Jan Kara
2012-05-17 21:35 ` Peter Zijlstra
2012-05-18 14:33 ` Jan Kara [this message]
2012-05-17 21:56 ` Peter Zijlstra
2012-05-18 14:42 ` Jan Kara
2012-05-18 10:43 ` Peter Zijlstra
2012-05-18 14:45 ` Jan Kara
2012-05-15 15:43 ` [PATCH 2/2] block: Convert BDI proportion calculations to flexible proportions Jan Kara
2012-05-17 22:04 ` Peter Zijlstra
2012-05-18 14:24 ` Jan Kara
2012-05-18 14:34 ` Peter Zijlstra
-- strict thread matches above, loose matches on Subject: below --
2012-05-24 16:59 [PATCH 0/2 v4] Flexible proportions Jan Kara
2012-05-24 16:59 ` [PATCH 1/2] lib: Proportions with flexible period Jan Kara
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