Re: [RFC PATCH] iothread: add set_iothread_poll_* commands

[Eric Blake <eblake@redhat.com>]

On 10/22/19 3:12 AM, yezhenyu (A) wrote:
> Since qemu2.9, QEMU added three AioContext poll parameters to struct
> IOThread: poll_max_ns, poll_grow and poll_shrink. These properties are
> used to control iothread polling time.
> 
> However, there isn't properly hmp commands to adjust them when the VM is
> alive. It's useful to adjust them online when observing the impact of
> different property value on performance.
> 
> This patch add three hmp commands to adjust iothread poll-* properties
> for special iothread:
> 
> set_iothread_poll_max_ns: set the maximum polling time in ns;
> set_iothread_poll_grow: set how many ns will be added to polling time;
> set_iothread_poll_shrink: set how many ns will be removed from polling
> time.
> 
> Signed-off-by: Zhenyu Ye <yezhenyu2@huawei.com>
> ---
> hmp-commands.hx | 42 ++++++++++++++++++++
> hmp.c | 30 +++++++++++++++
> hmp.h | 3 ++
> include/sysemu/iothread.h | 6 +++
> iothread.c | 80 +++++++++++++++++++++++++++++++++++++++
> qapi/misc.json | 23 +++++++++++
> 6 files changed, 184 insertions(+)

Looking at just the QMP...

> +++ b/qapi/misc.json
> @@ -675,6 +675,29 @@
> { 'command': 'query-iothreads', 'returns': ['IOThreadInfo'],
> 'allow-preconfig': true }
> 
> +##
> +# @set-iothread-poll-param:
> +#
> +# Set poll-* properties for a special iothread.
> +# The poll-* name can be poll_max_ns/poll_grow/poll_shrink.

This should be an enum.

> +#
> +# Notes: can not set the QEMU main loop thread, which is not declared
> +# using the -object iothread command-line option. The poll_ns property can not
> +# be set manually, which is auto-adjust.

You failed to document the parameters (iothread_id, name, value).

> +#
> +# Example:
> +#
> +# -> { "execute": "set-iothread-poll-param",
> +# "arguments": { "iothread_id": "1",
> +# "name": "poll_max_ns",
> +# "value": 1000 } }
> +# <- { "return": {} }
> +#
> +# Since 3.0

4.2 is the earliest this can make it in.

> +##
> +{ 'command': 'set-iothread-poll-param',
> + 'data': {'iothread_id': 'str', 'name': 'str', 'value': 'int'} }

Our naming convention prefers 'iothread-id'.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org