[Linux-ia64] Re: strange performance behaviour with floats

From: David Mosberger <davidm_at_napali.hpl.hp.com>
Date: 2003-02-25 06:12:39
>>>>> On Mon, 24 Feb 2003 13:25:12 +1100, Keith Owens <kaos@sgi.com> said:

  Keith> On Sun, 23 Feb 2003 18:16:57 -0800, 
  Keith> David Mosberger <davidm@napali.hpl.hp.com> wrote:
  >> Let me say this again: you _don't_ want a single-cycle loop.  You want
  >> a 2-cycle loop that gets twice the work done as a 1-cycle loop.  That
  >> is, you'd want to decrement the loop counter by 2, compare it against
  >> zero, and branch if it's not zero yet, all the while making sure you
  >> get a 2-cycle loop.

  Keith> Now I see what you are getting at, sorry for the confusion.

No problem. ;-)

  Keith> Of course, the fact that udelay() does not use bogomips at all makes
  Keith> the whole question irrelevant.  We now return you to our regularly
  Keith> scheduled delay loop :)

True, but the code gcc generates for the BogoMIPS loops basically
looks identical to the one for udelay(), so the comments still apply.

	--david
Received on Mon Feb 24 11:14:22 2003

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