Subject: Re: [PATCH v2 5/5] cmake: increase time-out for a long-running test

From: Victoria Dye <[email-masked]>
Date: Thu, 8 Sep 2022 10:29:35 -0700

Ævar Arnfjörð Bjarmason wrote:
> 
> On Tue, Aug 23 2022, Johannes Schindelin via GitGitGadget wrote:
> 
>> From: Johannes Schindelin <[email-masked]>
>>
>> As suggested in
>> https://github.com/git-for-windows/git/issues/3966#issuecomment-1221264238,
>> t7112 can run for well over one hour, which seems to be the default
>> maximum run time at least when running CTest-based tests in Visual
>> Studio.
>>
>> Let's increase the time-out as a stop gap to unblock developers wishing
>> to run Git's test suite in Visual Studio.
>>
>> Note: The actual run time is highly dependent on the circumstances. For
>> example, in Git's CI runs, the Windows-based tests typically take a bit
>> over 5 minutes to run. CI runs have the added benefit that Windows
>> Defender (the common anti-malware scanner on Windows) is turned off,
>> something many developers are not at liberty to do on their work
>> stations. When Defender is turned on, even on this developer's high-end
>> Ryzen system, t7112 takes over 15 minutes to run.
>>
>> Signed-off-by: Johannes Schindelin <[email-masked]>
>> ---
>>  contrib/buildsystems/CMakeLists.txt | 4 ++++
>>  1 file changed, 4 insertions(+)
>>
>> diff --git a/contrib/buildsystems/CMakeLists.txt b/contrib/buildsystems/CMakeLists.txt
>> index 29d7e236ae1..b1306f95256 100644
>> --- a/contrib/buildsystems/CMakeLists.txt
>> +++ b/contrib/buildsystems/CMakeLists.txt
>> @@ -1088,4 +1088,8 @@ foreach(tsh ${test_scipts})
>>  		WORKING_DIRECTORY ${CMAKE_SOURCE_DIR}/t)
>>  endforeach()
>>  
>> +# This test script takes an extremely long time and is known to time out even
>> +# on fast machines because it requires in excess of one hour to run
>> +set_tests_properties("${CMAKE_SOURCE_DIR}/t/t7112-reset-submodule.sh" PROPERTIES TIMEOUT 4000)
>> +
>>  endif()#BUILD_TESTING
> 
> I don't see per [1] that it would have any negative effect to just bump
> the timeout a lot more, and for all the tests.

I'm a bit confused as to how that link (which explains that the 'TIMEOUT'
property is used to determine when to kill a test process - more or less
standard behavior for timeouts in applications) shows that excessively long
timeouts on every test "[wouldn't] have any negative effect." 

In terms of the timeout length, the stated reason for adding the timeout in
the first place is:

>> Let's increase the time-out as a stop gap to unblock developers wishing
>> to run Git's test suite in Visual Studio.

I would consider ~1 hour a manageable (albeit frustrating) amount of time to
wait for a test, but not 10 hours (as you suggest later).

As for setting the timeout on all tests: that might be helpful, only because
(AFAICT from CMake's source code & documentation) the default timeout is "no
timeout." If setting a global default, though, I'd prefer a shorter timespan
(e.g. 1800s) so that a timeout properly indicates a failure condition ("this
test runs much longer than it should, so we may have introduced a
performance bug"). 

Practically, though, I don't feel too strongly about whether or not to set a
global default. If we wanted to add timeouts to more tests in the future,
I'd want a more extensible solution with carefully-selected timeouts. But if
it's just this one test running too long, special case-ing a timeout for it
with a comment explaining the reasoning seems appropriate to me. 

> 
> If we're running into 3600 seconds, then setting this to 4000 seconds
> seems to be a smal stopgap at best. That's just over a 10% increase, so
> if one person ran into it it 3600 someone with a slightly slower system
> should be running into the same still, or if we just add a few more
> tests to 7112 (or some other slow test).

I don't think this patch is suggesting that timeout failures are happening
at 3600s, rather that the peak observed execution time of the test is 3600s.
If that's the case, <peak execution time> + an 11% buffer is a reasonable
choice for the value.

> 
> So why not set this ta 3600*10 or whatever for *all* of the test scripts
> instead of playing whack-a-mole?
> 
> 1. https://cmake.org/cmake/help/latest/prop_test/TIMEOUT.html