floating point operations

[Peter Jeremy]

On Thu, Nov 01, 2007 at 10:40:04AM +1100, James Healy wrote:
>The remaining op is not easily converted to fixed point math, and we're
>wondering what impact a single flop on the receipt of each ACK will
>have. We don't have a strong understanding of the amount of overhead
>involved in executing a flop instead of an int op on modern hardware.

A single floating point operation in the kernel means that the kernel
must be adapted to allow floating point within it - saving userland FP
state somewhere between kernel entry and the FLOP, handling pesky
exceptions etc.  The problem is not the number of FLOPs in the kernel,
the problem is that the kernel is not currently setup to allow any
floating point within it.

This topic came up last week and I suggest you have a look at the
thread starting:
http://lists.freebsd.org/pipermail/freebsd-hackers/2007-October/022037.html

That said, I'm intrigued as to what operation you are stuck on.  I'm
having trouble visualising what you might be doing that gets stuck on
a single FP instruction.

-- 
Peter
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