[swift-corelibs-dev] [swift-dev] [Swift CI] Build Still Failing: 0. OSS - Swift Incremental RA - Ubuntu 16.10 (master) #3698

[David P Grove]

swift-dev-bounces at swift.org wrote on 05/17/2017 02:04:23 PM:
>
> Failure in dispatch-starfish. This test looks timing-sensitive.
> Boris, is this unlikely to be related to your changes? Does anyone
> familiar with dispatch have suggestions, such as increasing the
> latency threshold?
>
> [BEGIN] Latency
> Actual: 1553
> Expected: <1000
> [FAIL] Latency (dispatch_starfish.c:82)
> dispatch_starfish.c:82
> lap: 9
> count: 1000
> delta: 6756400000 ns
> math: 3374.825175 ns / lap
>
> [BEGIN] Latency
> Actual: 3374
> Expected: <1000
> [FAIL] Latency (dispatch_starfish.c:82)
> dispatch_starfish.c:82
>

The test is subject to failing spuriously if the machine is badly
overloaded.  One could increase the threshold by changing the #define on
line 43 of dispatch_starfish.c

There's a trade-off between spurious failures due to overloads on build
machines vs. missing performance regressions by making the latency
thresholds much too lenient.

We've been running with the current threshold in dispatch_starfish since we
began running the dispatch tests in the CI system last summer.  So if this
isn't a one-off failure caused by CI load, it might be pointing to an
underlying performance regression.

--dave
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