cmd/go: builds appear slower on openbsd/amd64 with Go 1.26rc2 (vs 1.25.6)

[4a6f656c]

When Go 1.26rc2 was being tested in the OpenBSD ports tree, it was noticed that Grafana was building slower than it had previously (with Go 1.25.6). Since the build machinery is building a large volume of packages, limitations are in place to prevent builds from trying to take over the entire machine - part of this appears to be (understandably) aggravated by GOMAXPROCS=1, however even increasing this to 2 or 4, there is still a seemingly ~5% slowdown in build time:

With -p=1 and GOMAXPROCS=1:

1.25.6:

   15m31.78s real    11m18.22s user     2m45.24s system                                                                                                                                                                                        

1.26rc2

   18m18.46s real    13m46.76s user     2m57.95s system

With -p=2 and GOMAXPROCS=2:

1.25.6:

   10m11.78s real    19m07.66s user     5m05.13s system

1.26rc2:

   10m38.15s real    19m31.14s user     5m27.86s system

With -p=2 and GOMAXPROCS=4:

1.25.6:

    9m21.32s real    23m38.35s user     7m13.84s system

1.26rc2:

    9m56.93s real    24m53.99s user     7m44.58s system

I've not had time to try to trace this further, or verify on other environments (not sure if it is potentially expected). Figured it was worth reporting all the same.

[gabyhelp]

Related Issues

• cmd/link: binary size increase with Go 1.26 #77235

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[dmitshur]

CC @golang/runtime.

[mknyszek]

CC @matloob @cherrymui who were looking at some build speed regressions recently. Has anything changed in 1.26rc3?

[cherrymui]

We did some change on how the go command sets parallelism when it invokes the compiler. However, I don't think that affects very small -p or GOMAXPROCS. Also, as the user time also increases, it is probably not due to the change in parallelism.

Would be good to try the RC3, and see if this is reproducible on platforms other than OpenBSD. Thanks.