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Re: indexing register

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On 8/24/2011 8:44 PM, MitchAlsup wrote:
> A) In general, I am a fan of flat register files and in particular when implementing SPARC V8s and V9s found that the windowed register files were a performance impediment and not a performance adder.
>
> B) Given that you have the ability to make such a large register file without harming performance (see A above) It is my considered opinion that you would get more performance by sharing that file across several threads than by adding registers to a single context.
>
> C) Can anyone name a machine with that 'took the performance world by storm' and also used more than 5-bits to index the register file(s)? {Note this wording expressively allows the CRAY 1 in because it indexes its register files with only 3-bits.}
>
> Mitch

Actually, Mitch, I think I'll take the opposite:

  register windows<< multiple threads with separate, disjoint, register 
files << a single thread with a big flat register file (and block on 
use) n multiple threads with variable sized register files partitioning 
a big RF

  Comparable: in system software, which would you rather do: write a 
really multithreaded program I or use as inch I/o?

  Myself, I would rather write the asynch I/o program as a single 
thread, for jobs like fast file copy or backup. Sure, given enough work 
the multithreaded version may heat the asynch I/oversion. But the best 
program willprobably need to do both, and the a synch I/o version is 
often low hanging fruit, easy to get a good speedup. I only jump to 
threads first when the computation is non-trivial, e.g. where I don't 
want to lock out user input while rendering.

Explanation: registers are rather like asynch I/O handles. The more such 
handles or registers, the more such parallelism under user control.

Yes, threads do the same, but threads always have overhead, in both HW & SW.

  (By the Way, I don't care to discuss a synch I/o implementations that 
require a Kernel thread for each asynch I/O. That's stupid. Asynch I/O 
handles can be much cheaper than a Kernel thread.

Variable size RFs per thread seem to have the best of both worlds.

  My main problem with variable size RFs, or large flat RFs in generals 
is architecture: I am by no means certain that multithreaded 
microarchitectures are the best for all systems. Back of the envelope 
calculations southeast MIMD are best in some cases. With small RFs. How 
does code written for a large RF run when there isn't one?

  I am not so concerned about fitting into a 32 bit instruction with S 
bit fields. Many codes that use flat large RFs fit in loop buffers, etc.

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Thread

indexing register Joe Keane <jgk@jgk.org> - 2011-08-24 19:36 +0000
  Re: indexing register Stephen Fuld <SFuld@alumni.cmu.edu.invalid> - 2011-08-24 13:38 -0700
  Re: indexing register MitchAlsup <MitchAlsup@aol.com> - 2011-08-24 18:44 -0700
    Re: indexing register "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-08-24 22:24 -0400
      Re: indexing register Quadibloc <jsavard@ecn.ab.ca> - 2011-08-24 20:08 -0700
        Re: indexing register Quadibloc <jsavard@ecn.ab.ca> - 2011-08-24 20:16 -0700
      Re: indexing register Thomas Womack <twomack@chiark.greenend.org.uk> - 2011-08-25 11:05 +0100
    Re: indexing register nmm1@cam.ac.uk - 2011-08-25 08:29 +0100
    Re: indexing register MitchAlsup <MitchAlsup@aol.com> - 2011-08-26 13:42 -0700
      Re: indexing register EricP <ThatWouldBeTelling@thevillage.com> - 2011-08-26 19:32 -0400
      Re: indexing register Robert Wessel <robertwessel2@yahoo.com> - 2011-08-26 18:53 -0500
        Re: indexing register "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-08-26 20:46 -0400
          Re: indexing register Robert Wessel <robertwessel2@yahoo.com> - 2011-08-26 23:34 -0500
            Re: indexing register mac <acolvin@efunct.com> - 2011-08-28 17:23 +0000
          Re: indexing register MitchAlsup <MitchAlsup@aol.com> - 2011-08-27 14:10 -0700
    Re: indexing register "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-08-27 18:19 -0500
    Re: indexing register "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-08-27 20:39 -0500
      Re: indexing register "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-08-28 20:59 -0700
    Re: indexing register jgk@panix.com (Joe keane) - 2011-08-29 21:59 +0000
  Re: indexing register Bakul Shah <usenet@bitblocks.com> - 2011-08-25 22:46 -0700
    Re: indexing register mac <acolvin@efunct.com> - 2011-08-26 14:06 +0000

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