Run tests with Server GC enabled & concurrent GC disabled.

[JoshKeegan]

Description

Maximises throughput over latency, reducing runtime for larger test packs or tests that will create a lot of objects on the heap.

Related issue

See discussion in #1967
There was also an older PR for these changes that got closed due to inactivity, that also contains some relevant discussion. See #1987

[MarcoRossignoli]

@nohwnd @Evangelink I think we should revert this one and add an option inside the runsetting for the host mode.

[cjprecord]

Would second the suggestion to revert this and add to runsettings.

This change is causing some issues on some test suites I have that test library code that is used to help with GC management for some soft realtime applications. With concurrent disabled in the test host any of the calls to

GCSettings.LatencyMode = GCLatencyMode.SustainedLowLatency;

Silently become a no-op with the mode staying as Batch (or Interactive if was previously changed) so the code that is verifying these expected state changes in the GCSettings are not able to be verified.

[Evangelink]

Hi @cjprecord, the change was actually reverted. We didn't do any runsettings option to enable it so we are back to previous state and so you shouldn't be experiencing any issue if you are using the stable release.

[cjprecord]

Hi @Evangelink, I had just updated to VS 17.4.2 the other day when started having this problem. Which eventually lead me to find that the the testhost app config files deployed with the installation appear to have this change in them with gcConcurrent set to false. Editing the file and setting to true I am able to run the tests successfully again.

Based on the date in the version, maybe the visual studio release picked up the version that still had the change in it

[MarcoRossignoli]

@cjprecord the revert will be included inside 17.4.3 release.