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

David Mosberger
2003-02-24T19:12:39Z

>>>>> 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