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From: Cort Dougan <cort@fsmlabs.com>
To: Linus Torvalds <torvalds@transmeta.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: Why Plan 9 C compilers don't have asm("")
Date: Fri, 6 Jul 2001 02:38:35 -0600	[thread overview]
Message-ID: <20010706023835.A5224@ftsoj.fsmlabs.com> (raw)
In-Reply-To: <200107040337.XAA00376@smarty.smart.net> <20010703233605.A1244@zalem.puupuu.org> <20010704002436.C1294@ftsoj.fsmlabs.com> <9hvjd4$1ok$1@penguin.transmeta.com>
In-Reply-To: <9hvjd4$1ok$1@penguin.transmeta.com>; from torvalds@transmeta.com on Wed, Jul 04, 2001 at 05:22:44PM +0000

I'm talking about _modern_ processors, not processors that dominate the
modern age.  This isn't x86.  I don't believe that even aggressive
re-ordering will cause a serious hit in performance on function calls.
Unconditional branches are definitely predictable so icache pre-fetches are
not more complicated that straight-line code.

Measurement is more important, though.  I've rejected a number of
optimizations from people (including many of my own) that were "obvious
enhancements" because of what they showed in real-world measurements.  If
it doesn't run faster, despite the theory being "right", it's worthless.

  reply	other threads:[~2001-07-06  8:38 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2001-07-04  3:37 Why Plan 9 C compilers don't have asm("") Rick Hohensee
2001-07-04  3:36 ` Olivier Galibert
2001-07-04  6:24   ` Cort Dougan
2001-07-04  8:03     ` H. Peter Anvin
2001-07-04 17:22     ` Linus Torvalds
2001-07-06  8:38       ` Cort Dougan [this message]
2001-07-06 18:44         ` Linus Torvalds
2001-07-06 20:02           ` Cort Dougan
2001-07-08 21:55           ` Victor Yodaiken
2001-07-08 22:28             ` Alan Cox
2001-07-09  1:22             ` Johan Kullstam
2001-07-08 22:29           ` David S. Miller
2001-07-06 11:43       ` David S. Miller
2001-07-21 22:10       ` Richard Henderson
2001-07-22  3:43         ` Linus Torvalds
2001-07-22  3:59           ` Mike Castle
2001-07-22  6:49           ` Richard Henderson
2001-07-22  7:44             ` Linus Torvalds
2001-07-22 15:53               ` Richard Henderson
2001-07-22 19:08                 ` Linus Torvalds
2001-07-04  7:15 ` pazke
2001-07-04 17:32 ` Don't feed the trooll [offtopic] " Ben LaHaise
2001-07-05  1:02 ` Michael Meissner
2001-07-05  1:54   ` Rick Hohensee
2001-07-05 16:54     ` Michael Meissner
2001-07-04 10:10 Rick Hohensee
2001-07-05  3:26 Rick Hohensee
2001-07-06 17:24 Rick Hohensee
2001-07-06 23:54 ` David S. Miller
2001-07-07  0:16   ` H. Peter Anvin
2001-07-07  0:37   ` David S. Miller
2001-07-07  6:16 Rick Hohensee
     [not found] <mailman.994629840.17424.linux-kernel2news@redhat.com>
2001-07-09  0:08 ` Pete Zaitcev
2001-07-09  0:28   ` Victor Yodaiken
2001-07-09  3:03 Rick Hohensee
2001-07-23  4:39 Rick Hohensee

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