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docs/devel/qgraph: add troubleshooting information 

It can be tricky to troubleshoot qos-test when a test won't execute. Add
an explanation of how to trace qgraph node connectivity and find which
node has the problem.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20210412143437.727560-3-stefanha@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2021-04-12 15:34:37 +01:00 committed by Thomas Huth
parent f62215298a
commit ce508a3c29
1 changed files with 58 additions and 0 deletions
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58
docs/devel/qgraph.rst
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@ -92,6 +92,64 @@ The basic framework steps are the following:
Depending on the QEMU binary used, only some drivers/machines will be
available and only test that are reached by them will be executed.
Troubleshooting unavailable tests
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
If there is no path from an available machine to a test then that test will be
unavailable and won't execute. This can happen if a test or driver did not set
up its qgraph node correctly. It can also happen if the necessary machine type
or device is missing from the QEMU binary because it was compiled out or
otherwise.
It is possible to troubleshoot unavailable tests by running::
$ QTEST_QEMU_BINARY=build/qemu-system-x86_64 build/tests/qtest/qos-test --verbose
# ALL QGRAPH EDGES: {
# src='virtio-net'
# |-> dest='virtio-net-tests/vhost-user/multiqueue' type=2 (node=0x559142109e30)
# |-> dest='virtio-net-tests/vhost-user/migrate' type=2 (node=0x559142109d00)
# src='virtio-net-pci'
# |-> dest='virtio-net' type=1 (node=0x55914210d740)
# src='pci-bus'
# |-> dest='virtio-net-pci' type=2 (node=0x55914210d880)
# src='pci-bus-pc'
# |-> dest='pci-bus' type=1 (node=0x559142103f40)
# src='i440FX-pcihost'
# |-> dest='pci-bus-pc' type=0 (node=0x55914210ac70)
# src='x86_64/pc'
# |-> dest='i440FX-pcihost' type=0 (node=0x5591421117f0)
# src=''
# |-> dest='x86_64/pc' type=0 (node=0x559142111600)
# |-> dest='arm/raspi2' type=0 (node=0x559142110740)
...
# }
# ALL QGRAPH NODES: {
# name='virtio-net-tests/announce-self' type=3 cmd_line='(null)' [available]
# name='arm/raspi2' type=0 cmd_line='-M raspi2 ' [UNAVAILABLE]
...
# }
The ``virtio-net-tests/announce-self`` test is listed as "available" in the
"ALL QGRAPH NODES" output. This means the test will execute. We can follow the
qgraph path in the "ALL QGRAPH EDGES" output as follows: '' -> 'x86_64/pc' ->
'i440FX-pcihost' -> 'pci-bus-pc' -> 'pci-bus' -> 'virtio-net-pci' ->
'virtio-net'. The root of the qgraph is '' and the depth first search begins
there.
The ``arm/raspi`` machine node is listed as "UNAVAILABLE". Although it is
reachable from the root via '' -> 'arm/raspi2' the node is unavailable because
the QEMU binary did not list it when queried by the framework. This is expected
because we used the ``qemu-system-x86_64`` binary which does not support ARM
machine types.
If a test is unexpectedly listed as "UNAVAILABLE", first check that the "ALL
QGRAPH EDGES" output reports edge connectivity from the root ('') to the test.
If there is no connectivity then the qgraph nodes were not set up correctly and
the driver or test code is incorrect. If there is connectivity, check the
availability of each node in the path in the "ALL QGRAPH NODES" output. The
first unavailable node in the path is the reason why the test is unavailable.
Typically this is because the QEMU binary lacks support for the necessary
machine type or device.
Creating a new driver and its interface
"""""""""""""""""""""""""""""""""""""""""