Re: [PATCH v4 3/3] util/event-loop-base: Introduce options to set the thread pool size

[Markus Armbruster]

Nicolas Saenz Julienne <nsaenzju@redhat.com> writes:

> On Fri, 2022-04-22 at 13:15 +0200, Markus Armbruster wrote:
>> Nicolas Saenz Julienne <nsaenzju@redhat.com> writes:
>> 
>> > The thread pool regulates itself: when idle, it kills threads until
>> > empty, when in demand, it creates new threads until full. This behaviour
>> > doesn't play well with latency sensitive workloads where the price of
>> > creating a new thread is too high. For example, when paired with qemu's
>> > '-mlock', or using safety features like SafeStack, creating a new thread
>> > has been measured take multiple milliseconds.
>> > 
>> > In order to mitigate this let's introduce a new 'EventLoopBase'
>> > property to set the thread pool size. The threads will be created during
>> > the pool's initialization or upon updating the property's value, remain
>> > available during its lifetime regardless of demand, and destroyed upon
>> > freeing it. A properly characterized workload will then be able to
>> > configure the pool to avoid any latency spikes.
>> > 
>> > Signed-off-by: Nicolas Saenz Julienne <nsaenzju@redhat.com>
>> > Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
>> 
>> [...]
>> 
>> > diff --git a/qapi/qom.json b/qapi/qom.json
>> > index e5f31c4469..06b8c3d10b 100644
>> > --- a/qapi/qom.json
>> > +++ b/qapi/qom.json
>> > @@ -506,9 +506,17 @@
>> >  #
>> >  # @aio-max-batch: maximum number of requests in a batch for the AIO 
>> > engine,
>> >  #                 0 means that the engine will use its default.
>> > +#
>> > +# @thread-pool-min: minimum number of threads readily available in the 
>> > thread
>> > +#                   pool (default:0, since 7.1)
>> 
>> What do you mean by "readily available in the thread pool"?
>
> How about "minimum number of threads reserved in the thread pool"?

Works for me, thanks!

>> > +#
>> > +# @thread-pool-max: maximum number of threads the thread pool can contain
>> > +#                   (default:64, since 7.1)
>> >  ##
>> 
>> If you add "Since: 7.1" in the previous patch, then the "since 7.1" here
>> need to go.
>
> Noted.