When doing a NOP build of Chrome (ninja -n chrome, make sure you have explicitly run "gn gen" first) the StartEdge and FinishCommand stages consume most of the time (use -d stats to see this). StartEdge takes ~20 s and FinishCommand takes ~8 s. The vast majority of this (on my workstation) is spent in creating and deleting .rsp files. This was confirmed when I did ETW profiling of the NOP build which showed that the vast majority of this time was in the OS - in kernel functions or perhaps in anti-virus.

This overhead means that a NOP build of chrome (with jumbo and goma enabled so there are "only" 25,470 build steps) takes ~36 s. Experiments with disabling of .rsp creation and deletion shows that it reduces the NOP build time to ~8 s.

The effect on 'real' builds is unknown but it is possible that the absolute savings may be similar, or at least the .rsp file creation savings may apply.