On Fri, Mar 10, 2017 at 12:48:31 +0100, Peter Maydell wrote: > On 10 March 2017 at 12:45, Dr. David Alan Gilbert <dgilb...@redhat.com> wrote: > > * Emilio G. Cota (c...@braap.org) wrote: > >> x86_64 NBench Floating Point Performance > >> Host: Intel(R) Xeon(R) CPU E5-2690 0 @ 2.90GHz > >> > >> 1.88 > >> +-+-+---+--+---+---+---+--+---+---+---+---+--+---+---+---+--+---+-+-+ > >> | + + + *A*#*A* + + + + + + + + + + + + > >> | > >> 1.86 +-+ *** *** > >> +-+ > >> | # # *A*#*** > >> | > >> | *A*# # # ## *A* > >> | > >> 1.84 +-+ # *A* *A* # > >> +-+ > >> | # # *A* > >> | > >> 1.82 +-+ # # ## > >> +-+ > >> | # *A*# # > >> | > >> 1.8 +-+ # # #*A* *A* > >> +-+ > >> | # *A* # # > >> | > >> 1.78 +-+*A* # *A* # > >> +-+ > >> | # ***# # # > >> | > >> | *A*#*A* # # > >> | > >> 1.76 +-+ *** # # > >> +-+ > >> | + + + + + + + + + + + + + + *A* + + > >> | > >> 1.74 > >> +-+-+---+--+---+---+---+--+---+---+---+---+--+---+---+---+--+---+-+-+ > >> v1.v1.v1.2v1.3v1.4v1.v1.6v1.7v2.0v2.1v2.v2.3v2.4v2.5v2.v2.7v2.8.0 > >> QEMU version > > > > I'm assuming the dips are where QEMU fixed something and cared about corner > > cases/accuracy? > > Given the scale on the LHS is from 1.74 to 1.88 my guess is that the > variation is in large part noise and the major thing is "our fp > performance is bounded by softfloat, which doesn't change and is > always very slow".
It isn't "measurement noise" -- if you look at the PNGs the measurements are very stable (all points have error bars): http://imgur.com/a/nF7Ls It's true that performance here varies very little. This is just the result of Amdahl's law, as you point out. (upon re-reading your message, I see that perhaps what you meant by "noise" is exactly this.) E.