Re: Could an Intel 486 wake up with FC3

From: James Wilkinson (james_at_westexe.demon.co.uk)
Date: 01/31/05

  • Next message: James Wilkinson: "Re: Could an Intel 486 wake up with FC3" 
    Date: Mon, 31 Jan 2005 19:26:46 +0000
To: For users of Fedora Core releases <fedora-list@redhat.com>

    Aleksandar Milivojevic wrote:
    > On the sidenote, since i586 is minimal supported platform, I don't know
    > why packages are still built as i386, and not as i586.

    *Very* frequently asked question in some quarters. The short answer is
    that it doesn't appear to be worth it.

    There were very few instructions added to the instruction set between
    the 386 and the 686, and apparently most of those that were added
    aren't the sort of instructions that noticably accelerate programs.

    The exceptions, the instructions that do help performance, give better
    control of spinlocks and multi-threaded code. That does help, especially
    on multi-processor kit, but the code that uses those instructions tends
    to be abstracted into glibc, which *is* compiled for the different
    processors. [1]

    In the meantime, some surprisingly recent kit (VIA CPUs, for example)
    don't include all the 686 support.

    The Fedora development crew have repeatedly said that they would be very
    interested to see benchmarks that prove a particular program would
    benefit from different compile settings. [2] But they do expect these
    benchmarks to be rigourous: same kit, the same location on the drive (if
    relevant), system rebooted between runs, just different compile flags.

    As you say, these days the programs are *optimised* for Pentium 4s:
    apparently this works well for most other modern x86 CPUs.

    James.

    [1] Remember that all these programs are cross-platform: they can't rely
    on running on an Intel-compatible processor, so the Right Thing is
    usually to push this sort of thing into an OS library.

    [2] That includes things like changing -O2 (compile for speed, at least
    on small program segments) to -Os (compile for size, which will use
    caches better). Stuff that really can change performance levels. 

    -- 
James Wilkinson       | "The US Air Force is removing harmful "greenhouse"
Exeter    Devon    UK | gases from the cooling systems of intercontinental
E-mail address: james | ballistic missiles. This will minimise damage to the
@westexe.demon.co.uk  | ozone layer in the event of a nuclear holocaust."
                      |     -- The Guardian.
-- 
fedora-list mailing list
fedora-list@redhat.com
To unsubscribe: http://www.redhat.com/mailman/listinfo/fedora-list
  • Next message: James Wilkinson: "Re: Could an Intel 486 wake up with FC3"

    Relevant Pages

    • Re: CREATE
      ... possible code field address. ... defining word's definition. ... SEP instructions. ... The only difference being that, at compile time, VARIABLE ...
      (comp.lang.forth)
    • Re: Create, edit file list?
      ... Randy - I just redid ... Using "Start with Full Compile" ... > from the site code following the instructions there and it worked right ... folders on a drive using the DirListBox and FileListBox controls. ...
      (microsoft.public.vb.general.discussion)
    • Re: real time linux
      ... >> least that these new controls would have to use technology which is ... >> ability to edit and compile on the control. ... > B) Pick up the Nail ... > A vector architecture would issue all of the instructions at once, ...
      (alt.machines.cnc)
    • Re: JIT and addresses
      ... If I compile the following lines of code and break the execution with ... instructions to addresses way up in the address space. ... public static void a ... 0000001a nop ...
      (microsoft.public.dotnet.framework.clr)
    Loading