Build-time tests fail if machine has a single CPU

Build-time tests fail if machine has a single CPU

[Santiago Vila via lttng-dev]

Hello.

When I try to build (the Debian package of) lttng-tools (which in
Debian is called ltt-control for the source package name) on AWS
instances of type m7a.medium or r7a.medium (which incidentally have a
single vCPU) I get the following error while running the tests:

make[7]: Entering directory '/<<PKGBUILDDIR>>/tests/regression'
FAIL: tools/lttng-ctl/test_robust_protocol.py 1 - test_simple - Exception: ('enable-channel --session session_lrmmg1mr --userspace channel_qmx5kx61 --buffer-allocation=per-cpu --buffer-ownership=user', '<?xml version="1.0" encoding="UTF-8"?>\n<command xmlns="https://lttng.org/xml/ns/lttng-mi" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="https://lttng.org/xml/ns/lttng-mi https://lttng.org/xml/schemas/lttng-mi/4/lttng-mi-4.2.xsd" schemaVersion="4.2"><name>enable-channel</name><output><channels/><success>false</success></output></command>\n', "Error: Exception when getting CPU count: Failed to parse possible CPU mask: mask_contents=`0\n`\nError: Not enough system memory available for channel 'channel_qmx5kx61'. At least 0MiB required, 0MiB available\n")
ERROR: tools/lttng-ctl/test_robust_protocol.py - exited with status 1
ERROR: ust/test_no_event_timestamps.py - Bail out! Missing 1 test cases
PASS: ust/ust-constructor/test_ust_constructor_cpp_static.py 1 - Create a session
FAIL: ust/ust-constructor/test_ust_constructor_cpp_static.py 2 - Add a channel to session `session_dx6uww4i`
ERROR: ust/ust-constructor/test_ust_constructor_cpp_static.py - Bail out! Missing 42 test cases
PASS: ust/ust-constructor/test_ust_constructor_cpp_dynamic.py 1 - Create a session
FAIL: ust/ust-constructor/test_ust_constructor_cpp_dynamic.py 2 - Add a channel to session `session_nwjtsjz6`
ERROR: ust/ust-constructor/test_ust_constructor_cpp_dynamic.py - Bail out! Missing 42 test cases
PASS: ust/ust-constructor/test_ust_constructor_c_static.py 1 - Create a session
FAIL: ust/ust-constructor/test_ust_constructor_c_static.py 2 - Add a channel to session `session_xwec7bzr`
ERROR: ust/ust-constructor/test_ust_constructor_c_static.py - Bail out! Missing 22 test cases
ERROR: ust/high-throughput/test_high_throughput_snapshot.py - Bail out! Missing 3 test cases
SKIP: ust/high-throughput/test_high_throughput.py 1 # SKIP : Long regression tests not enabled
ERROR: tools/client/test_reclaim_memory.py - Bail out! Missing 2 test cases
PASS: tests.serial 1 - Test script 'tools/base-path/test_ust' returned code 0. 42 passed, 0 failed, 0 skipped, 42 planned [total: 42]
FAIL: tests.serial 2 - Test script 'tools/channel/test_channel' returned code 1. 15 passed, 1 failed, 0 skipped, 16 planned [total: 16]
FAIL: tests.serial 3 - Test script 'tools/channel/test_cli_legacy_channel_buffering_policies.py' returned code 1. 0 passed, 0 failed, 0 skipped, 6 planned [total: 0]


Note 1: the message saying "Not enough system memory available" is
probably false, as the machine has 4GB or 8GB of RAM, and I don't get
those messages when using the same amount of memory with 2 CPUs.

Note 2: One way to reproduce this easily on any machine is to configure
GRUB with GRUB_CMDLINE_LINUX="nr_cpus=1".

Thanks.

Re: Build-time tests fail if machine has a single CPU

[Santiago Vila via lttng-dev]

I forgot one detail which might help to debug the issue:

This started to happen in version 2.14.0.
Version 2.13.15 worked ok.

Thanks.

Re: Build-time tests fail if machine has a single CPU

[Kienan Stewart via lttng-dev]

Hi Santiago,

thanks for the bug report. I'll take a look at it.

kienan

On 3/9/26 1:12 PM, Santiago Vila via lttng-dev wrote:
> I forgot one detail which might help to debug the issue:
> 
> This started to happen in version 2.14.0.
> Version 2.13.15 worked ok.
> 
> Thanks.

Re: Build-time tests fail if machine has a single CPU

[Kienan Stewart via lttng-dev]

Hi Santiago,

some changes have been merged into the master branch that should fix the 
issue you're facing. They should be backported into the next bug-fix 
release for 2.14

[1]: 
https://github.com/lttng/lttng-tools/commit/41e650ca6d7587fd217f276b6e9af19cd962b7da
[2]: 
https://github.com/lttng/lttng-tools/commit/519c2e6c6b286d33d3c4b4d8a5032317392e0939
[3]: 
https://github.com/lttng/lttng-tools/commit/562507728d13b7c3544d2059f9f891f9c82109a4
[4]: 
https://github.com/lttng/lttng-tools/commit/f1d33a72a5ffb1515f66b0af8b9044df93efd970
[5]: 
https://github.com/lttng/lttng-tools/commit/2a857d8fe56c76bc25b35cb8ecde5e8687412694

thanks,
kienan

On 3/9/26 3:02 PM, Kienan Stewart via lttng-dev wrote:
> Hi Santiago,
> 
> thanks for the bug report. I'll take a look at it.
> 
> kienan
> 
> On 3/9/26 1:12 PM, Santiago Vila via lttng-dev wrote:
>> I forgot one detail which might help to debug the issue:
>>
>> This started to happen in version 2.14.0.
>> Version 2.13.15 worked ok.
>>
>> Thanks.
>