On 02/26/2013 10:41 AM, Torbjorn Granlund wrote: > I'm not sure quite what's going on with the 3/4 issue rates. I really would > have expected to see either exactly 1, or very nearly 1/2, especially for > vadd. > > I think you mean 4/3. But also that is an underestimate. with 8-way > unrolling I get a bit more, about 7/5.
I guess I should have written the units used: cyc/insn. Which is why 5 makes sense in my table for chained multiplies, as opposed to some bizzaro-land where the latency of a multiply is 1/5 or 2 tenths of a cycle. I really did mean that I measured 4 adds issued per 3 cycles. But you're also right that increased unrolling measures slightly better, issuing 12 insns in 8.5 cycles, or < 1% difference from your 5/7. r~ _______________________________________________ gmp-devel mailing list gmp-devel@gmplib.org http://gmplib.org/mailman/listinfo/gmp-devel