Re: [PATCH mptcp-next] Squash-to: "selftests: mptcp: tweak simult_flows for debug kernels"

[Mat Martineau <mathew.j.martineau@linux.intel.com>]

On Tue, 28 Jun 2022, Matthieu Baerts wrote:

> Hi Mat,
>
> On 27/06/2022 23:44, Mat Martineau wrote:
>> kbuild is still seeing intermittent failures in the simult_flows.sh
>> test. It uses a kernel config without kmemleak, but with other
>> performance-affecting debug options like lockdep and kasan.
>>
>> Example failures:
>> kernel-selftests.net/mptcp.simult_flows.sh.unbalanced_bwidth_with_unbalanced_delay_transfer_slower_than_expected!_runtime_4339_ms_expected_4005_ms_max_4005.fail
>> kernel-selftests.net/mptcp.simult_flows.sh.unbalanced_bwidth_transfer_slower_than_expected!_runtime_4285_ms_expected_4005_ms_max_4005.fail
>> kernel-selftests.net/mptcp.simult_flows.sh.unbalanced_bwidth_transfer_slower_than_expected!_runtime_4346_ms_expected_4005_ms_max_4005.fail
>
> If I'm not mistaken, adding 200ms would not prevent these failures if
> you got 4346ms instead of 4005ms, right? It looks like we need to extend
> the time to something around 350ms.
>

I had thought the "slack" was calculated differently, but I think you're 
correct here. I am a little reluctant to increase the limit too far, since 
the whole point is to detect when the transfers become slower - and we 
seem to instead keep finding slower CI systems!

What do you think about this approach: make simult_flows.sh 'SKIP' when 
debug kernel features are detected, unless a "-f" flag forces it to run? 
That way we could run it with debug features where we know the system 
performance, like our CI, but not show bogus failures on random 
debug-enabled systems.


>> Adjust the debug detection to loosen the simult_flows timing constraints
>> if either kmemleak or lockdep are configured.
>
> Good idea!
> I didn't find any "safe" ways to easily check that KASAN is used.
>
> Checking dmesg doesn't seem to be a safe way for all environments.
>
> But maybe we could do this? (with '-q')
>
>  $ grep mm/kasan /sys/devices/system/cpu/hotplug/states/sys/devices
>  /system/cpu/hotplug/states:70:214: mm/kasan:online
>

How about:

grep -q ' kmemleak_init$\| lockdep_init$\| kasan_init$\| prove_locking$' /proc/kallsyms

?

That detects the compiled-in features, rather than what's enabled at 
runtime, but it's simple and may be good enough.

--
Mat Martineau
Intel