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

[Nicolas Saenz Julienne <nsaenzju@redhat.com>]

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"?

> > +#
> > +# @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.

-- 
Nicolás Sáenz