By the way if you happen to be looking at the Python plugin, then
there are two changes that may be worth using.
API_VERSION = 2:
https://libguestfs.org/nbdkit-python-plugin.3.html#API-versions
and multi-thread support:
https://libguestfs.org/nbdkit-python-plugin.3.html#Threads
These were both added (by you) and are both available in nbdkit >= 1.22,
which is now available in RHEL AV >= 8.3.0 so there's no reason why we
can't use them now.
Great
I don't think there's any advantage to API_VERSION = 2 because the
plugin is very (exclusively?) write-heavy. But a more parallel thread
model is surely advantageous?
I think we can change the rhv upload plugin to use this approach:
plugins/python/examples/imageio.py
Based on the tests I did with the imageio plugin this should
give significant performance improvement.
I think the changes are basically:
api version: 2
thread model: parallel
open:
- Create a connection pool instead of a single connection.
- Based on experience wit imageio client, 4 connections are a good default
pwrite/zero/pread:
- Get connection from the pool, blocking for available instance
- Return the connection to the pool when done or after failure
flush:
- send a flush request for all connections in the pool
(each http connection have a separate nbd connection inside imageio)
close:
- close all connections in pool
What do you think?
For API_VERSION = 2, the changes are:
* pread signature changes to:
def pread(h, buf, offset, flags) -> returns nothing
- You have to write the result directly into the buf parameter,
avoiding the extra copy.
* pwrite adds flags parameter:
def pwrite(h, buf, offset, flags) -> returns nothing
* flush, trim also add flags parameter.
* zero changes signature completely, removing the may_trim parameter
and adding a general flags parameter in its place.
For threads:
* Add a thread_model() function with no parameters which returns
nbdkit.THREAD_MODEL_PARALLEL or nbdkit.THREAD_MODEL_SERIALIZE_REQUESTS.
Of course locking will need to be introduced (especially for
PARALLEL) to protect internal data structures. See nbdkit-plugin(3)
for an explanation of the thread models.
You'll also have to change the minimum version of nbdkit so that older
versions get rejected, here:
https://github.com/libguestfs/virt-v2v/blob/1d5fc257765c444644e5bfc6525e86ff201755f0/v2v/output_rhv_upload.ml#L87
Rich.
--
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
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