cmd/go: frequent test timeouts on dragonfly-amd64 builder

[bcmills]

2021-03-24T03:16:14-4357f71/dragonfly-amd64
2021-03-23T23:09:33-87a3ac5/dragonfly-amd64
2021-03-23T01:21:24-d25476e/dragonfly-amd64
2021-03-19T17:31:59-4829031/dragonfly-amd64
2021-03-19T16:11:47-a937729/dragonfly-amd64
2021-03-18T21:27:21-d3ab6b5/dragonfly-amd64
2021-03-18T21:22:04-bdbba22/dragonfly-amd64
2021-03-18T17:14:39-f47fab9/dragonfly-amd64
2021-03-18T16:51:27-eaa1dde/dragonfly-amd64
2021-03-18T16:51:24-af4388a/dragonfly-amd64
2021-03-18T04:17:00-c2d6251/dragonfly-amd64

The timeouts don't seem to occur in any one particular test case, and no individual test case seems to be running for an inordinately long time. I think this builder is just slow, but I'm filing this issue in case there is a specific performance problem in cmd/go or the test itself that we can address.

I wonder if something about the dragonfly kernel or the builder configuration in particular makes the I/O syscalls used by cmd/go slower than on other platforms.

CC @tuxillo @jayconrod @matloob

[tuxillo]

Probably it is the setup. Each builder is running in a VM but the virtual disks are stored in hard disks, not SSDs. Also, we have to periodically cleanup the filesystem more often than in a standard setup, in which the cleanup occurs once a day. If they are causing too much trouble, I could probably move the VMs to another server. Let me know!