Did you check to see what GOGC=100 vs GOGC=500 look like now that you’ve moved up to Go 1.8? Really it sounds like there was a CPU starvation bug in Go 1.6 that was fixed in a later release. That could have been the dominant cause of your slowdown and might mean you don’t need to tune GOGC at all. At the least, the effect of GOGC should be less, and it would be nice to know how much less. Thanks for taking the time to write the post.