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

[Zhenyu Ye <yezhenyu2@huawei.com>]

On 2019/10/23 23:19, Stefan Hajnoczi wrote:
> On Tue, Oct 22, 2019 at 04:12:03PM +0800, 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(+)
> 
> poll-max-ns, poll-grow, poll-shrink are properties of IOThread objects.
> They can already be modified at runtime using:
> 
>   $ qemu -object iothread,id=iothread1
>   (qemu) qom-set /objects/iothread1 poll-max-ns 100000
> 
> I think there is no need for a patch.
> 
> Stefan
> 

Thanks for your review. I have considered using the `qom-set` command to modify
IOThread object's properties, however, this command is not friendly to primary
users. The help info for this command is only:

    qom-set path property value -- set QOM property

It's almost impossible to get the correct `path` parameter for primary user.

This patch provides a more convenient and easy-use hmp&qmp interface to modify
these IOThread properties. I think this patch still has a little value.

And I can implement this patch compactly by reusing your code.

Waiting for your reply.