From: Stephen Hemminger <shemminger@linux-foundation.org>
To: Andi Kleen <andi@firstfloor.org>
Cc: Jan Engelhardt <jengelh@linux01.gwdg.de>,
linux-kernel@vger.kernel.org, netdev@vger.kernel.org
Subject: Re: [RFC] div64_64 support
Date: Mon, 5 Mar 2007 15:57:14 -0800 [thread overview]
Message-ID: <20070305155714.3abe1b5e@freekitty> (raw)
In-Reply-To: <p73slcnawh3.fsf@bingen.suse.de>
On 03 Mar 2007 03:31:52 +0100
Andi Kleen <andi@firstfloor.org> wrote:
> Stephen Hemminger <shemminger@linux-foundation.org> writes:
>
> > Here is another way to handle the 64 bit divide case.
> > It allows full 64 bit divide by adding the support routine
> > GCC needs.
>
> Not supplying that was intentional by Linus so that people
> think twice (or more often) before they using such expensive
> operations. A plain / looks too innocent.
>
> Is it really needed by CUBIC anyways? It uses it for getting
> the cubic root, but the algorithm recommended by Hacker's Delight
> (great book) doesn't use any divisions at all. Probably better
> to use a better algorithm without divisions.
>
I tried the code from Hacker's Delight.
It is cool, but performance is CPU (and data) dependent:
Average # of usecs per operation:
Hacker Newton
Pentium 3 68.6 < 90.4
T2050 98.6 > 92.0
U1400 450 > 415
Xeon 70 < 90
Xeon (newer) 71 < 78
EM64T 21.8 < 24.6
AMD64 23.4 < 32.0
It might be worth the change for code size reduction though.
--
Stephen Hemminger <shemminger@linux-foundation.org>
next prev parent reply other threads:[~2007-03-05 23:57 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-02-24 1:05 [RFC] div64_64 support Stephen Hemminger
2007-02-24 16:19 ` Sami Farin
2007-02-26 20:09 ` Jan Engelhardt
2007-02-26 21:28 ` Stephen Hemminger
2007-02-27 1:20 ` H. Peter Anvin
2007-02-27 3:45 ` Segher Boessenkool
2007-02-26 22:31 ` Stephen Hemminger
2007-02-26 23:02 ` Jan Engelhardt
2007-02-26 23:44 ` Stephen Hemminger
2007-02-27 0:05 ` Jan Engelhardt
2007-02-27 0:07 ` Stephen Hemminger
2007-02-27 0:14 ` Jan Engelhardt
2007-02-27 6:21 ` Dan Williams
2007-03-03 2:31 ` Andi Kleen
2007-03-05 23:57 ` Stephen Hemminger [this message]
2007-03-06 0:25 ` David Miller
2007-03-06 13:36 ` Andi Kleen
2007-03-06 14:04 ` [RFC] div64_64 support II Andi Kleen
2007-03-06 17:43 ` Dagfinn Ilmari Mannsåker
2007-03-06 18:25 ` David Miller
2007-03-06 18:48 ` H. Peter Anvin
2007-03-06 13:34 ` [RFC] div64_64 support Andi Kleen
2007-03-06 14:19 ` Eric Dumazet
2007-03-06 14:45 ` Andi Kleen
2007-03-06 15:10 ` Roland Kuhn
2007-03-06 18:29 ` Stephen Hemminger
2007-03-06 19:48 ` Andi Kleen
2007-03-06 20:04 ` Stephen Hemminger
2007-03-06 21:53 ` Sami Farin
2007-03-06 22:24 ` Sami Farin
2007-03-07 16:11 ` Chuck Ebbert
2007-03-07 18:32 ` Sami Farin
2007-03-08 18:23 ` asm volatile [Was: [RFC] div64_64 support] Sami Farin
2007-03-08 22:01 ` asm volatile David Miller
2007-03-06 21:58 ` [RFC] div64_64 support David Miller
2007-03-06 22:47 ` [PATCH] tcp_cubic: faster cube root Stephen Hemminger
2007-03-06 22:58 ` cube root benchmark code Stephen Hemminger
2007-03-07 6:08 ` Update to " Willy Tarreau
2007-03-08 1:07 ` [PATCH] tcp_cubic: use 32 bit math Stephen Hemminger
2007-03-08 2:55 ` David Miller
2007-03-08 3:10 ` Stephen Hemminger
2007-03-08 3:51 ` David Miller
2007-03-10 11:48 ` Willy Tarreau
2007-03-12 21:11 ` Stephen Hemminger
2007-03-13 20:50 ` Willy Tarreau
2007-03-21 18:54 ` Stephen Hemminger
2007-03-21 19:15 ` Willy Tarreau
2007-03-21 19:58 ` Stephen Hemminger
2007-03-21 20:15 ` [PATCH 1/2] div64_64 optimization Stephen Hemminger
2007-03-21 20:17 ` [PATCH 2/2] tcp: cubic optimization Stephen Hemminger
2007-03-22 19:11 ` David Miller
2007-03-22 19:11 ` [PATCH 1/2] div64_64 optimization David Miller
2007-03-08 4:16 ` [PATCH] tcp_cubic: use 32 bit math Willy Tarreau
2007-03-07 4:20 ` [PATCH] tcp_cubic: faster cube root David Miller
2007-03-07 12:12 ` Andi Kleen
2007-03-07 19:33 ` David Miller
2007-03-06 18:50 ` [RFC] div64_64 support H. Peter Anvin
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