Re: [PULL 3/9] tests/migration: Reduce autoconverge initial bandwidth

[Philippe Mathieu-Daudé]

On 6/9/20 7:00 PM, Dr. David Alan Gilbert wrote:
> * Michael S. Tsirkin (mst@redhat.com) wrote:
>> On Wed, Mar 25, 2020 at 01:16:26PM +0000, Dr. David Alan Gilbert (git) wrote:
>>> From: Philippe Mathieu-Daudé <philmd@redhat.com>
>>>
>>> When using max-bandwidth=~100Mb/s, this test fails on Travis-CI
>>> s390x when configured with --disable-tcg:
>>>
>>>   $ make check-qtest
>>>     TEST    check-qtest-s390x: tests/qtest/boot-serial-test
>>>   qemu-system-s390x: -accel tcg: invalid accelerator tcg
>>>   qemu-system-s390x: falling back to KVM
>>>     TEST    check-qtest-s390x: tests/qtest/pxe-test
>>>     TEST    check-qtest-s390x: tests/qtest/test-netfilter
>>>     TEST    check-qtest-s390x: tests/qtest/test-filter-mirror
>>>     TEST    check-qtest-s390x: tests/qtest/test-filter-redirector
>>>     TEST    check-qtest-s390x: tests/qtest/drive_del-test
>>>     TEST    check-qtest-s390x: tests/qtest/device-plug-test
>>>     TEST    check-qtest-s390x: tests/qtest/virtio-ccw-test
>>>     TEST    check-qtest-s390x: tests/qtest/cpu-plug-test
>>>     TEST    check-qtest-s390x: tests/qtest/migration-test
>>>   **
>>>   ERROR:tests/qtest/migration-test.c:1229:test_migrate_auto_converge: 
>>> 'got_stop' should be FALSE
>>>   ERROR - Bail out! 
>>> ERROR:tests/qtest/migration-test.c:1229:test_migrate_auto_converge: 
>>> 'got_stop' should be FALSE
>>>   make: *** [tests/Makefile.include:633: check-qtest-s390x] Error 1
>>>
>>> Per David Gilbert, "it could just be the writing is slow on s390
>>> and the migration thread fast; in which case the autocomplete
>>> wouldn't be needed. Perhaps we just need to reduce the bandwidth
>>> limit."
>>>
>>> Tuning the threshold by reducing the initial bandwidth makes the
>>> autoconverge test pass.
>>>
>>> Suggested-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
>>> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
>>> Message-Id: <20200323184015.11565-1-philmd@redhat.com>
>>> Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
>>> Tested-by: Alex Bennée <alex.bennee@linaro.org>
>>> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
>>
>>
>> This slows make check down significantly for me, it stays
>> at the migration test for minutes.
> 
> Is this on the s390x version or all of them?

Personally I only noticed it on s390x.

Alex have you seen another arch?

> 
>> I'm carrying a revert at top of my tree for now but I'd rather
>> not need that.
>>
>>
>> This seems like a fragile way to test things anyway.
>> What happens if someone slows writing even more
>> e.g. because it's running in a container or a VM?
>>
>> How about detecting that migration finished too early
>> and slowing it down until autocomplete triggers?
> 
> THe problem is you can't rely on any form of consistency in a heavily
> contended container, so the fact that it took n-seconds to migrate at
> this attempt means very little about what the next attempt will take.
> 
> Dave
> 
>>
>>
>>> ---
>>>  tests/qtest/migration-test.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/tests/qtest/migration-test.c b/tests/qtest/migration-test.c
>>> index 3d6cc83b88..2568c9529c 100644
>>> --- a/tests/qtest/migration-test.c
>>> +++ b/tests/qtest/migration-test.c
>>> @@ -1211,7 +1211,7 @@ static void test_migrate_auto_converge(void)
>>>       * without throttling.
>>>       */
>>>      migrate_set_parameter_int(from, "downtime-limit", 1);
>>> -    migrate_set_parameter_int(from, "max-bandwidth", 100000000); /* 
>>> ~100Mb/s */
>>> +    migrate_set_parameter_int(from, "max-bandwidth", 1000000); /* ~1Mb/s */
>>>  
>>>      /* To check remaining size after precopy */
>>>      migrate_set_capability(from, "pause-before-switchover", true);
>>> -- 
>>> 2.25.1
>>>
>>>
>>
> --
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
>