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2022-05-09util/event-loop-base: Introduce options to set the thread pool sizeNicolas Saenz Julienne1-0/+23
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> Acked-by: Markus Armbruster <armbru@redhat.com> Message-id: 20220425075723.20019-4-nsaenzju@redhat.com Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2022-05-09util/main-loop: Introduce the main loop into QOMNicolas Saenz Julienne1-0/+13
'event-loop-base' provides basic property handling for all 'AioContext' based event loops. So let's define a new 'MainLoopClass' that inherits from it. This will permit tweaking the main loop's properties through qapi as well as through the command line using the '-object' keyword[1]. Only one instance of 'MainLoopClass' might be created at any time. 'EventLoopBaseClass' learns a new callback, 'can_be_deleted()' so as to mark 'MainLoop' as non-deletable. [1] For example: -object main-loop,id=main-loop,aio-max-batch=<value> Signed-off-by: Nicolas Saenz Julienne <nsaenzju@redhat.com> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> Acked-by: Markus Armbruster <armbru@redhat.com> Message-id: 20220425075723.20019-3-nsaenzju@redhat.com Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2022-05-09Introduce event-loop-base abstract classNicolas Saenz Julienne1-0/+104
Introduce the 'event-loop-base' abstract class, it'll hold the properties common to all event loops and provide the necessary hooks for their creation and maintenance. Then have iothread inherit from it. EventLoopBaseClass is defined as user creatable and provides a hook for its children to attach themselves to the user creatable class 'complete' function. It also provides an update_params() callback to propagate property changes onto its children. The new 'event-loop-base' class will live in the root directory. It is built on its own using the 'link_whole' option (there are no direct function dependencies between the class and its children, it all happens trough 'constructor' magic). And also imposes new compilation dependencies: qom <- event-loop-base <- blockdev (iothread.c) And in subsequent patches: qom <- event-loop-base <- qemuutil (util/main-loop.c) All this forced some amount of reordering in meson.build: - Moved qom build definition before qemuutil. Doing it the other way around (i.e. moving qemuutil after qom) isn't possible as a lot of core libraries that live in between the two depend on it. - Process the 'hw' subdir earlier, as it introduces files into the 'qom' source set. No functional changes intended. Signed-off-by: Nicolas Saenz Julienne <nsaenzju@redhat.com> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> Acked-by: Markus Armbruster <armbru@redhat.com> Message-id: 20220425075723.20019-2-nsaenzju@redhat.com Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>