[PATCH v3 10/15] include: Introduce typed params for virDomainSetIOThreadParams wrt pool size

[Michal Prívozník]

On 6/29/22 16:19, Daniel P. Berrangé wrote:
> On Wed, Jun 08, 2022 at 03:43:04PM +0200, Michal Privoznik wrote:
>> Our public API offers virDomainSetIOThreadParams() function which
>> allows users to set various aspects of IOThreads. Introduce two
>> new typed parameters: VIR_DOMAIN_IOTHREAD_THREAD_POOL_MIN and
>> VIR_DOMAIN_IOTHREAD_THREAD_POOL_MAX which will allow users to
>> modify the thread-pool-min and thread-pool-max attributes of an
>> iothread.
>>
>> Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
>> Reviewed-by: Peter Krempa <pkrempa at redhat.com>
>> ---
>>  include/libvirt/libvirt-domain.h | 28 ++++++++++++++++++++++++++++
>>  1 file changed, 28 insertions(+)
>>
>> diff --git a/include/libvirt/libvirt-domain.h b/include/libvirt/libvirt-domain.h
>> index 2aec69bc54..1ea3284e63 100644
>> --- a/include/libvirt/libvirt-domain.h
>> +++ b/include/libvirt/libvirt-domain.h
>> @@ -2499,6 +2499,34 @@ int                  virDomainDelIOThread(virDomainPtr domain,
>>   */
>>  # define VIR_DOMAIN_IOTHREAD_POLL_SHRINK "poll_shrink"
>>  
>> +/**
>> + * VIR_DOMAIN_IOTHREAD_THREAD_POOL_MIN:
>> + *
>> + * Sets the lower bound for thread pool size. A value of -1 disables this bound
>> + * leaving hypervisor use its default value, though this value is not accepted
>> + * for running domains. Due to internal implementation it's recommended to set
>> + * VIR_DOMAIN_IOTHREAD_THREAD_POOL_MIN and VIR_DOMAIN_IOTHREAD_THREAD_POOL_MAX
>> + * separately. Accepted type is VIR_TYPED_PARAM_INT.
> 
> 
> What's the story with this comment about setting pool-min and pool-max
> separately ?
> 
> This feels like a impl detail that should never be exposed in the API.
> 
> If we need to set them separately with QEMU, then the QEMU driver
> should make separate QMP calls to set them as needed. The app should
> never have to care about this.

The story is that min and max values are set in separate monitor
commands (qom-set). So depending on the current values, min has to be
set before max or vice verca. So we would need a logic that gets the
current values and acts accordingly. While I agree it's not user
friendly, we can implement the logic later. Or do you want to make it
before the release?

Michal