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runtime: TestSmhasherWindowed failures on linux-386-longtest builder #39352

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bcmills opened this issue Jun 1, 2020 · 6 comments
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runtime: TestSmhasherWindowed failures on linux-386-longtest builder #39352

bcmills opened this issue Jun 1, 2020 · 6 comments
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@bcmills
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@bcmills bcmills commented Jun 1, 2020

Now that the linux-386-longtest builder is correctly running the tests in 386 mode (as of CL 234520), it seems to be shaking out some flakiness in TestSmhasherWindowed (CC @randall77):

2020-06-01T20:38:23-13bc6d4/linux-386-longtest
2020-05-29T20:56:20-6ad5f4e/linux-386-longtest

@bcmills bcmills added this to the Backlog milestone Jun 1, 2020
@randall77
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@randall77 randall77 commented Jun 1, 2020

Are we seeing this on any other 386 builder? It seems strange that it would only occur on Windows.

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@randall77 randall77 commented Jun 1, 2020

Sorry, nevermind, it happens on linux-386-longtest also.

@bcmills
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@bcmills bcmills commented Jun 1, 2020

Erm, that was a typo anyway. We don't actually have a 32-bit Windows longtest builder.

@randall77 randall77 self-assigned this Jun 12, 2020
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@randall77 randall77 commented Jun 12, 2020

I'm pretty sure we just need to raise the threshold a bit. I've investigated the collisions that happen, and they all seem to be pairwise, so they are not a big deal.
"pairwise" = when there are 32 collisions, it is two keys mapping to the same hash, 32 times, not 33 keys all mapping to the same hash.

It happens on the 386 builder because the hash results are only 32 bits. On the 64 bit builders the hash is 64 bits, which makes collisions much less likely.

@gopherbot
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@gopherbot gopherbot commented Jun 12, 2020

Change https://golang.org/cl/237718 mentions this issue: runtime: raise alert threshold on window smhasher test

@gopherbot gopherbot closed this in 8dae539 Jun 12, 2020
@dmitshur dmitshur modified the milestones: Backlog, Go1.15 Aug 21, 2020
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