runtime: TestSmhasherWindowed is still flaky on linux-386-longtest #43130

bcmills · 2020-12-11T02:39:32Z

2020-12-10T22:58:49-6d3d3fb/linux-386-longtest

##### GOMAXPROCS=2 runtime -cpu=1,2,4 -quick
--- FAIL: TestSmhasherWindowed (27.87s)
    hash_test.go:566: 32 bit keys
    hash_test.go:161: unexpected number of collisions: got=512 mean=0.499992 stddev=0.707101 threshold=156.565200
    hash_test.go:568: 64 bit keys
    hash_test.go:570: string keys
--- FAIL: TestSmhasherWindowed (26.69s)
    hash_test.go:566: 32 bit keys
    hash_test.go:161: unexpected number of collisions: got=512 mean=0.499992 stddev=0.707101 threshold=156.565200
    hash_test.go:568: 64 bit keys
    hash_test.go:570: string keys
--- FAIL: TestSmhasherWindowed (26.69s)
    hash_test.go:566: 32 bit keys
    hash_test.go:161: unexpected number of collisions: got=512 mean=0.499992 stddev=0.707101 threshold=156.565200
    hash_test.go:568: 64 bit keys
    hash_test.go:570: string keys
FAIL
FAIL	runtime	598.996s

2020-10-26T21:47:49-36c5edd/linux-386-longtest

--- FAIL: TestSmhasherWindowed (26.23s)
    hash_test.go:566: 32 bit keys
    hash_test.go:161: unexpected number of collisions: got=512 mean=0.499992 stddev=0.707101 threshold=156.565200
    hash_test.go:568: 64 bit keys
    hash_test.go:161: unexpected number of collisions: got=512 mean=0.499992 stddev=0.707101 threshold=156.565200
    hash_test.go:570: string keys
FAIL
FAIL	runtime	169.624s

See previously #39352.

I would guess that it's flaky on 32-bit ARM too, but we don't have a longtest builder for that configuration.

CC @randall77

The text was updated successfully, but these errors were encountered:

bcmills · 2021-01-25T14:41:32Z

2021-01-22T23:03:58-25c39e4/linux-386-longtest

--- FAIL: TestSmhasherWindowed (26.54s)
    hash_test.go:566: 32 bit keys
    hash_test.go:568: 64 bit keys
    hash_test.go:570: string keys
    hash_test.go:161: unexpected number of collisions: got=514 mean=0.499992 stddev=0.707101 threshold=156.565200
    hash_test.go:161: unexpected number of collisions: got=256 mean=0.499992 stddev=0.707101 threshold=156.565200
FAIL
FAIL	runtime	182.398s

gopherbot · 2021-03-05T02:58:06Z

Change https://golang.org/cl/280372 mentions this issue: runtime: using wyhash for memhashFallback on 32bit platform

wyhash is a general hash function that: 1. Default hash function of Zig, Nim 2. Passed Smhasher, BigCrush and PractRand 3. Less code 4. 3~26% faster than internal hashmap name old time/op new time/op delta Hash5 67.8ns ± 0% 65.4ns ± 0% -3.45% (p=0.000 n=7+10) Hash16 82.5ns ± 0% 74.2ns ± 0% -10.12% (p=0.000 n=6+8) Hash64 121ns ± 0% 102ns ± 0% -15.82% (p=0.000 n=7+10) Hash1024 1.13µs ± 0% 0.89µs ± 0% -20.58% (p=0.000 n=10+9) Hash65536 68.9µs ± 0% 54.4µs ± 0% -21.04% (p=0.000 n=10+7) HashStringSpeed 103ns ± 2% 93ns ± 3% -10.24% (p=0.000 n=9+10) HashBytesSpeed 191ns ± 2% 180ns ± 1% -5.40% (p=0.000 n=10+8) HashInt32Speed 59.0ns ± 2% 59.1ns ± 1% ~ (p=0.655 n=9+8) HashInt64Speed 72.7ns ± 3% 66.1ns ± 5% -9.04% (p=0.000 n=10+10) HashStringArraySpeed 270ns ± 1% 222ns ± 2% -17.91% (p=0.000 n=10+10) FastrandHashiter 108ns ± 0% 109ns ± 1% +0.96% (p=0.002 n=10+10) name old speed new speed delta Hash5 73.8MB/s ± 0% 76.4MB/s ± 0% +3.58% (p=0.000 n=7+10) Hash16 194MB/s ± 0% 216MB/s ± 0% +11.25% (p=0.000 n=10+8) Hash64 530MB/s ± 0% 630MB/s ± 0% +18.74% (p=0.000 n=8+10) Hash1024 910MB/s ± 0% 1145MB/s ± 0% +25.88% (p=0.000 n=10+9) Hash65536 951MB/s ± 0% 1204MB/s ± 0% +26.64% (p=0.000 n=10+7) Update #43130 Change-Id: Id00c54b116a2411fcf675e95896fffb85f0e25b6 Reviewed-on: https://go-review.googlesource.com/c/go/+/280372 Trust: Meng Zhuo <mzh@golangcn.org> Run-TryBot: Meng Zhuo <mzh@golangcn.org> TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Keith Randall <khr@golang.org>

bcmills · 2021-08-05T14:24:03Z

2021-08-04T15:26:45-6e73886/linux-386-longtest
2021-02-25T19:57:49-6c3bcda/linux-386-longtest
2021-02-23T19:55:03-a671e33/linux-386-longtest

mengzhuo · 2022-01-06T06:33:44Z

@bcmills Unfortunately even after 483533d is merged It still failed.

Good news is it failed at the rate 1 failure per month and 256 collisions instead of 512.

I'll check whether my implement same with original wyhash :-(

mengzhuo · 2022-01-07T07:34:19Z

Updates: I've run 32 bits SmhasherWindow for 4770 times (~24h) without failures...

bcmills · 2022-01-20T02:43:35Z

Indeed, still failing about once a month (and that's including the lower rate of test runs due to the code freeze). The more recent failures are back to 512 collisions each.

greplogs --dashboard -md -l -e '(?ms)FAIL: TestSmhasherWindowed.*unexpected number of collisions' --since=2021-09-24

2022-01-19T20:54:49-1efc581/linux-386-longtest
2021-12-19T20:16:45-87b2a54/linux-386-longtest
2021-11-15T21:22:17-e08aae2/linux-386-longtest
2021-10-23T12:44:47-b0f7eb6/linux-386-longtest

mengzhuo · 2022-01-20T06:58:43Z

Indeed, still failing about once a month (and that's including the lower rate of test runs due to the code freeze). The more recent failures are back to 512 collisions each.

Recently a new version of Smhasher is released with the "bad seed" testcase, which wyhash is failed ( caused by multiply 0).
Maybe we can skip "bad seed" on 32 bit platforms and regain a "good seed" in the alginit procedure.

bcmills · 2022-02-03T19:30:51Z

@mengzhuo, at the very least would it be useful to have the test log the seed(s) that produced the unexpected collision rate? That would help to verify that this test failure is due to the expected bad seeds.

bcmills · 2022-02-03T19:32:21Z

Marking as release-blocker for Go 1.19: linux/386 is a first-class port, but it's probably too late in the 1.18 cycle to fully fix this without introducing too much risk.

mengzhuo · 2022-02-08T09:25:31Z

My mistake: 386 using AES asm part do the hashing, I will take a look.

------Original comment-------------------------------
@randall77 Keith,

This issue can be reproduced within 6000 times run on 64 bit keys SmhasherWindow test.

After I deleted these 4 lines, no more flaky (12K runs):

go/src/runtime/alg.go

Lines 325 to 328 in 69e1711

    
           hashkey[0] |= 1 // make sure these numbers are odd 
        
           hashkey[1] |= 1 
        
           hashkey[2] |= 1 
        
           hashkey[3] |= 1

I think the OR itself cancel the randomness of last bit (always 1)

But when I tried XOR

hashkey[0] ^= 1

there are flaky failures.

gopherbot · 2022-02-09T02:45:50Z

Change https://go.dev/cl/384075 mentions this issue: runtime: AES maphash scramble 3 times on 386

mengzhuo · 2022-02-13T15:03:49Z

Unfortunatly, it still flaky within 1/40000 and the key and seed seems random enough to me.

    hash_test.go:119: aeskey 7c3fcff1e80c0a0a9a13ce82b08c0ed80192f93e919b702a728c7bee2b6be56b86146ea040eee7a85d17efc794474ef83465567cd588569ca13945feaec28df3
    hash_test.go:120: unexpected number of collisions: got=256 mean=0.499992 stddev=0.707101 threshold=156.565200

According to the smhasher, some hashing algorithm based on AES failed the test.
Is it the AES itself is not qualified as a hashing algorithm?

bcmills · 2022-03-30T20:02:19Z

greplogs --dashboard -md -l -e 'FAIL: TestSmhasherWindowed' --since=2022-02-08

2022-03-21T18:58:42-79103fa/linux-386-longtest

bcmills · 2022-04-12T13:20:24Z

greplogs --dashboard -md -l -e 'FAIL: TestSmhasherWindowed' --since=2022-03-30

2022-04-11T22:03:44-0605bf6/linux-386-longtest

bcmills · 2022-04-22T14:51:06Z

greplogs --dashboard -md -l -e 'FAIL: TestSmhasherWindowed' --since=2022-04-12

2022-04-21T23:45:36-67d6be1/linux-386-longtest

bcmills · 2022-04-22T14:53:03Z

@golang/runtime: this is a recurring failure on linux/386, which is a first class port. Could someone take a look at this and either fix it (if feasible) or add a test skip (if this turns out not to be a priority)?

gopherbot · 2022-04-26T23:34:46Z

Change https://go.dev/cl/402456 mentions this issue: runtime: disable windowed Smhasher test on 32-bit systems

bcmills added Testing NeedsInvestigation labels Dec 11, 2020

bcmills added this to the Backlog milestone Dec 11, 2020

bcmills modified the milestones: Backlog, Go1.19 Feb 3, 2022

bcmills added the release-blocker label Feb 3, 2022

gopherbot closed this as completed in be0d049 Feb 9, 2022

bcmills reopened this Mar 30, 2022

gopherbot closed this as completed in 68b655f Apr 27, 2022

golang locked and limited conversation to collaborators Apr 27, 2023

gopherbot added the FrozenDueToAge label Apr 27, 2023

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runtime: TestSmhasherWindowed is still flaky on linux-386-longtest #43130

runtime: TestSmhasherWindowed is still flaky on linux-386-longtest #43130

bcmills commented Dec 11, 2020

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runtime: TestSmhasherWindowed is still flaky on linux-386-longtest #43130

runtime: TestSmhasherWindowed is still flaky on linux-386-longtest #43130

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