From: Thomas Sailer <sailer@sailer.dynip.lugs.ch>
To: Linus Torvalds <torvalds@osdl.org>
Cc: Grzegorz Kulewski <kangur@polcom.net>,
Alan <alan@lxorguk.ukuu.org.uk>,
Mikael Pettersson <mikpe@it.uu.se>,
s0348365@sms.ed.ac.uk, 76306.1226@compuserve.com, akpm@osdl.org,
bunk@stusta.de, greg@kroah.com, linux-kernel@vger.kernel.org,
yanmin_zhang@linux.intel.com
Subject: Re: kernel + gcc 4.1 = several problems
Date: Wed, 03 Jan 2007 22:44:19 +0100 [thread overview]
Message-ID: <1167860659.13394.41.camel@unreal> (raw)
In-Reply-To: <Pine.LNX.4.64.0701030731080.4473@woody.osdl.org>
On Wed, 2007-01-03 at 08:03 -0800, Linus Torvalds wrote:
> and assuming the branch is AT ALL predictable (and 95+% of all branches
> are), the branch-over will actually be a LOT better for a CPU.
IF... Counterexample: Add-Compare-Select in a Viterbi Decoder. If the
compare can be predicted, you botched the compression of the data (if
you can predict the data, you could have compressed it better), or your
noise is not white, i.e. you f*** up the whitening filter. So in any
practical viterbi decoder, the compares cannot be predicted. I remember
cmov made a big difference in Viterbi Decoder performance on a Cyrix
6x86. But granted, nowadays these things are usually done with SIMD and
masks.
Tom
next prev parent reply other threads:[~2007-01-03 22:29 UTC|newest]
Thread overview: 60+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-01-03 2:12 kernel + gcc 4.1 = several problems Mikael Pettersson
2007-01-03 2:20 ` Alistair John Strachan
2007-01-05 15:53 ` Alistair John Strachan
2007-01-05 16:02 ` Linus Torvalds
2007-01-05 16:19 ` Alistair John Strachan
2007-01-05 16:49 ` Linus Torvalds
2007-01-07 0:36 ` Pavel Machek
2007-01-07 0:57 ` Alistair John Strachan
2007-01-03 5:55 ` Willy Tarreau
2007-01-03 10:29 ` Alan
2007-01-03 10:32 ` Grzegorz Kulewski
2007-01-03 11:51 ` Jeff Garzik
2007-01-03 12:44 ` Alan
2007-01-03 13:32 ` Arjan van de Ven
2007-01-03 13:58 ` Jakub Jelinek
2007-01-03 14:28 ` Alan
2007-01-03 16:06 ` Linus Torvalds
2007-01-03 16:03 ` Linus Torvalds
2007-01-03 17:01 ` l.genoni
2007-01-03 17:45 ` Tim Schmielau
2007-01-03 20:24 ` Linus Torvalds
2007-01-03 17:06 ` l.genoni
2007-01-03 17:53 ` Mariusz Kozlowski
2007-01-03 19:47 ` Denis Vlasenko
2007-01-03 20:38 ` Linus Torvalds
2007-01-03 21:48 ` Denis Vlasenko
2007-01-03 22:13 ` Linus Torvalds
2007-01-03 21:44 ` Thomas Sailer [this message]
2007-01-03 22:08 ` Linus Torvalds
2007-01-04 3:08 ` Zou, Nanhai
2007-01-04 15:34 ` Linus Torvalds
-- strict thread matches above, loose matches on Subject: below --
2007-01-04 7:11 Albert Cahalan
2007-01-04 16:43 ` Segher Boessenkool
2007-01-04 17:04 ` Albert Cahalan
2007-01-04 17:24 ` Segher Boessenkool
2007-01-04 17:47 ` Linus Torvalds
2007-01-04 18:53 ` Segher Boessenkool
2007-01-04 19:10 ` Al Viro
2007-01-05 17:17 ` Pavel Machek
2007-01-06 8:23 ` Segher Boessenkool
2007-01-04 17:37 ` Linus Torvalds
2007-01-04 18:34 ` Segher Boessenkool
2007-01-04 22:02 ` Geert Bosch
2007-01-07 4:25 ` Denis Vlasenko
2007-01-07 4:45 ` Linus Torvalds
2007-01-07 5:26 ` Jeff Garzik
2007-01-07 15:10 ` Segher Boessenkool
2007-01-26 22:05 ` Michael K. Edwards
2007-01-04 18:08 ` Andreas Schwab
2006-12-20 14:21 Oops in 2.6.19.1 Alistair John Strachan
2006-12-30 16:59 ` Alistair John Strachan
2006-12-31 16:27 ` Adrian Bunk
2006-12-31 16:55 ` Alistair John Strachan
2007-01-02 21:10 ` kernel + gcc 4.1 = several problems Adrian Bunk
2007-01-02 21:56 ` Alistair John Strachan
2007-01-02 22:06 ` D. Hazelton
2007-01-02 23:24 ` Adrian Bunk
2007-01-02 23:41 ` D. Hazelton
2007-01-03 2:05 ` Horst H. von Brand
2007-01-02 22:13 ` Linus Torvalds
2007-01-02 23:18 ` Alistair John Strachan
2007-01-03 1:43 ` Linus Torvalds
2007-01-02 22:01 ` Linus Torvalds
2007-01-02 23:09 ` David Rientjes
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