Re: [PATCH V1 0/6] fast qom tree get

[Steven Sistare <steven.sistare@oracle.com>]

On 4/28/2025 4:04 AM, Markus Armbruster wrote:
> Steven Sistare <steven.sistare@oracle.com> writes:
> 
>> On 4/9/2025 3:39 AM, Markus Armbruster wrote:
>>> Hi Steve, I apologize for the slow response.
>>>
>>> Steve Sistare <steven.sistare@oracle.com> writes:
>>>
>>>> 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.
>>>
>>> "Some managers"... could you name one?
>>
>> My personal experience is with Oracle's OCI, but likely others could benefit.
> 
> Elsewhere in this thread, we examined libvirt's use qom-get.  Its use of
> qom-get is also noticably slow, and your work could speed it up.
> However, most of its use is for working around QMP interface
> shortcomings around probing CPU flags.  Addressing these would help it
> even more.
> 
> This makes me wonder what questions Oracle's OCI answers with the help
> of qom-get.  Can you briefly describe them?
> 
> Even if OCI would likewise be helped more by better QMP queries, your
> fast qom tree get work might still be useful.

We already optimized our queries as a first step, but what remains is still
significant, which is why I submitted this RFE.

- Steve