Using qom-list and qom-get to get all the nodes and property values in a
QOM tree can take multiple seconds because it requires 1000's of individual
QOM requests. Some managers fetch the entire tree or a large subset
of it when starting a new VM, and this cost is a substantial fraction of
start up time.
To reduce this cost, consider QAPI calls that fetch more information in
each call:
* qom-list-get: given a path, return a list of properties and values.
* qom-list-getv: given a list of paths, return a list of properties and
values for each path.
* qom-tree-get: given a path, return all descendant nodes rooted at that
path, with properties and values for each.
In all cases, a returned property is represented by ObjectPropertyValue,
with fields name, type, value, and error. If an error occurs when reading
a value, the value field is omitted, and the error message is returned in the
the error field. Thus an error for one property will not cause a bulk fetch
operation to fail.
To evaluate each method, I modified scripts/qmp/qom-tree to use the method,
verified all methods produce the same output, and timed each using:
qemu-system-x86_64 -display none \
-chardev socket,id=monitor0,path=/tmp/vm1.sock,server=on,wait=off \
-mon monitor0,mode=control &
time qom-tree -s /tmp/vm1.sock > /dev/null
I only measured once per method, but the variation is low after a warm up run.
The 'real - user - sys' column is a proxy for QEMU CPU time.
method real(s) user(s) sys(s) (real - user - sys)(s)
qom-list / qom-get 2.048 0.932 0.057 1.059
qom-list-get 0.402 0.230 0.029 0.143
qom-list-getv 0.200 0.132 0.015 0.053
qom-tree-get 0.143 0.123 0.012 0.008
qom-tree-get is the clear winner, reducing elapsed time by a factor of 14X,
and reducing QEMU CPU time by 132X.
qom-list-getv is slower when fetching the entire tree, but can beat
qom-tree-get when only a subset of the tree needs to be fetched (not shown).
qom-list-get is shown for comparison only, and is not included in this series.
Steve Sistare (6):
qom: qom_resolve_path
qom: qom-tree-get
python: use qom-tree-get
tests/qtest/qom-test: unit test for qom-tree-get
qom: qom-list-getv
tests/qtest/qom-test: unit test for qom-list-getv
python/qemu/utils/qom.py | 36 +++++------
python/qemu/utils/qom_common.py | 50 ++++++++++++++++
qapi/qom.json | 93 ++++++++++++++++++++++++++++
qom/qom-qmp-cmds.c | 130 ++++++++++++++++++++++++++++++++++++++--
tests/qtest/qom-test.c | 116 +++++++++++++++++++++++++++++++++++
5 files changed, 401 insertions(+), 24 deletions(-)
base-commit: 354925d42252f6f36a9e1e4a6b929aaafb2eaf45
--
1.8.3.1
