LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: David Miller <davem@davemloft.net>
To: shemminger@linux-foundation.org
Cc: andi@firstfloor.org, jengelh@linux01.gwdg.de,
linux-kernel@vger.kernel.org, netdev@vger.kernel.org
Subject: Re: [RFC] div64_64 support
Date: Mon, 05 Mar 2007 16:25:51 -0800 (PST) [thread overview]
Message-ID: <20070305.162551.41660347.davem@davemloft.net> (raw)
In-Reply-To: <20070305155714.3abe1b5e@freekitty>
From: Stephen Hemminger <shemminger@linux-foundation.org>
Date: Mon, 5 Mar 2007 15:57:14 -0800
> I tried the code from Hacker's Delight.
> It is cool, but performance is CPU (and data) dependent:
>
> Average # of usecs per operation:
Interesting results.
The problem with these algorithms that tradoff one or more
multiplies in order to avoid a divide is that they don't
give anything and often lose when both multiplies and
divides are emulated in software.
This is particularly true in this cube-root case from Hacker's
Delight, because it's using 3 multiplies per iteration in place of one
divide per iteration.
Actually, sorry, there is only one real multiply in there since the
other two can be computed using addition and shifts.
Another thing is that the non-Hacker's Delight version iterates
differently for different input values, so the input value space is
very important to consider when comparing these two pieces of code.
next prev parent reply other threads:[~2007-03-06 0:25 UTC|newest]
Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-02-24 1:05 Stephen Hemminger
2007-02-24 16:19 ` Sami Farin
2007-02-26 19:28 ` Stephen Hemminger
2007-02-26 19:39 ` David Miller
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
2007-03-06 0:25 ` David Miller [this message]
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 0:00 ` Stephen Hemminger
2007-03-07 0:05 ` David Miller
2007-03-07 0:05 ` 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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20070305.162551.41660347.davem@davemloft.net \
--to=davem@davemloft.net \
--cc=andi@firstfloor.org \
--cc=jengelh@linux01.gwdg.de \
--cc=linux-kernel@vger.kernel.org \
--cc=netdev@vger.kernel.org \
--cc=shemminger@linux-foundation.org \
--subject='Re: [RFC] div64_64 support' \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).