net/http/pprof: TestDeltaProfile failures missing mutexHog2 on ARM architectures

[bcmills]

--- FAIL: TestDeltaProfile (53.30s)
    pprof_test.go:206: want mutexHog2 but no mutexHog1 in the profile, and non-zero p.DurationNanos, got PeriodType: contentions count
        Period: 1
        Time: 2021-12-16 19:51:59.42219359 +1100 AEDT
        Duration: 32.041535781s
        Samples:
        contentions/count delay/nanoseconds
        Locations
        Mappings
        1: 0x0/0x0/0x0   [FN]
    pprof_test.go:214: want both mutexHog1 and mutexHog2 in the profile, got PeriodType: contentions count
        Period: 1
        Time: 2021-12-16 19:51:59.43107526 +1100 AEDT
        Samples:
        contentions/count delay/nanoseconds
                  9   17621016: 1 2 3 
                  1     149081: 1 4 3 
        Locations
             1: 0x851d3 M=1 sync.(*Mutex).Unlock /home/gopher/build/go/src/sync/mutex.go:214 s=0
             2: 0x2d249f M=1 net/http/pprof.mutexHog1 /home/gopher/build/go/src/net/http/pprof/pprof_test.go:107 s=0
             3: 0x2d2937 M=1 net/http/pprof.mutexHog.func1 /home/gopher/build/go/src/net/http/pprof/pprof_test.go:148 s=0
             4: 0x2d24ab M=1 net/http/pprof.mutexHog1 /home/gopher/build/go/src/net/http/pprof/pprof_test.go:108 s=0
        Mappings
        1: 0x0/0x0/0x0   [FN]
FAIL
FAIL	net/http/pprof	57.491s

greplogs --dashboard -md -l -e 'FAIL: TestDeltaProfile ' --since=2021-01-01

2021-12-16T00:34:10-7f23145/openbsd-arm-jsing
2021-11-25T00:02:52-b2a5a37/openbsd-arm-jsing
2021-06-04T17:33:24-831f937/openbsd-arm-jsing

(Forked from #38544, which was mitigated in CL 229498.)

CC @4a6f656c @hyangah

[gopherbot]

Change https://golang.org/cl/372794 mentions this issue: net/http/pprof: skip TestDeltaProfile on openbsd/arm

[bcmills]

greplogs --dashboard -md -l -e 'FAIL: TestDeltaProfile ' --since=2021-12-17

2022-02-04T22:34:05-f9763a6/android-arm64-corellium

[bcmills]

Given the android/arm64 failure, this does not seem specific to OpenBSD.
(CC @cherrymui)

[bcmills]

Another android/arm64 today:

greplogs --dashboard -md -l -e 'FAIL: TestDeltaProfile ' --since=2022-02-05

2022-02-07T21:00:02-7db75b3/android-arm64-corellium

[gopherbot]

Change https://go.dev/cl/383997 mentions this issue: net/http/pprof: skip TestDeltaProfile on all arm and arm64 architectures

[bcmills]

I suspect it may be possible to use something along the lines of the awaitBlockedGoroutine function from CL 384534 to eliminate the timing-dependence of this test.

(I do not plan to follow up on that myself.)