[Date Prev][Date Next] [Thread Prev][Thread Next] [Date Index] [Thread Index]

Re: Why does X need so much CPU power?

Wayne Gemmell <wayneg@ananzi.co.za> writes:

> Excuse my ignorance but couldn't the problem (at least in some part) lie in 
> the fact that everything is coded/compiled for a 386?

See the list archives; this is practically a FAQ.  The answer always
seems to be "no, except for very specialized things like linear
algebra and cryptography, and those actually do use processor-specific

> Surely code could at least run more efficiently with code that is
> compiled to use things like MMX, MMX2 and 3Dnow technology?

All three of those are basically the same technology, along with SSE;
it's adding a short vector unit to the normal processor path.  It's
designed to help things like video work, where you have three or four
(or maybe as many as 8 or 16) sets of values that you're performing
the same computation on.  I believe things like this can become
not-a-loop, and thus more efficient:

  float a[4], b[4], c[4], d[4];
  float alpha;
  for (int i = 0; i < 4; i++)
    c[i] = a[i] + b[i];   // vector-vector add
    d[i] = c[i] * alpha;  // vector-scalar multiply

But this isn't what run-of-the-mill code looks like; it's not going to
help things like laying out a Web page in response to parsed HTML.

David Maze         dmaze@debian.org      http://people.debian.org/~dmaze/
"Theoretical politics is interesting.  Politicking should be illegal."
	-- Abra Mitchell

Reply to: