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

[Philippe Mathieu-Daudé]

On 6/9/20 6:36 PM, Michael S. Tsirkin 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.

Alex Bennée reported the same problem, I don't know what is the best way
to fix this.

> 
> 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?

This seems to be the problem I noticed and tried to fix.

> 
> How about detecting that migration finished too early
> and slowing it down until autocomplete triggers?

David, I am a bit clueless with this code, do you mind having a look?

We can revert this test and disable the s390x runner, but it is our only
big-endian host, which recently show to be useful.

> 
>> ---
>>  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
>>
>>
>