"WASTED WORK ON THE INTEL CORE I7", slide#12 (page 13 in pdf) is fascinating to me. But I want to know how the data was collected, and what the % wasted work actually means.
40% wasted work, does that mean that they checked the branch-predictor and found that 40% of the time was spent on (wrongfully) speculated branches?
It also suggests that for all of the power-efficiency faults of branch predictors (aka: running power-consuming computations when it was "unnecessary"), the best you could do is maybe a 40% reduction in power consumption (no task seems to be 40% inefficient).
> People seem to think every i5 or i7 is the same.
Unfortunately, this is a feature, not a bug. Intel wants their branding to have this effect... the lay-person isn't supposed to understand Sandy Bridge (i7-2700k) vs Skylake (i7-6700k)
40% wasted work, does that mean that they checked the branch-predictor and found that 40% of the time was spent on (wrongfully) speculated branches?
It also suggests that for all of the power-efficiency faults of branch predictors (aka: running power-consuming computations when it was "unnecessary"), the best you could do is maybe a 40% reduction in power consumption (no task seems to be 40% inefficient).