zbus Priority Boost
Overview
This sample implements a simple application that illustrates the priority boost feature. The application implements the below figure scenario. When the priority boost feature is disabled, the execution sequence presents a priority inversion problem, which may not affect much of the developer’s application. Those who want to avoid priority inversions between message subscribers and plain subscribers should use the priority boost strategy.
ZBUS_CHAN_DEFINE(chan_a,
int,
NULL,
NULL,
ZBUS_OBSERVERS(l1, ms1, ms2, s1, l2),
0
);
Note
The developer must use the zbus_obs_attach_to_thread() function to ensure a proper
priority boost execution.
Building and Running
The figure below illustrates the execution of the cited scenario but with the priority boost disabled.
It can be built and executed on QEMU as follows:
# From the root of the zephyr repository
west build -b qemu_x86 samples/subsys/zbus/priority_boost -- -DCONFIG_ZBUS_PRIORITY_BOOST=n
west build -t run
Sample Output
I: --------------
I: 0 -> T1: prio before 5
I: 0 ---> L1: T1 prio 5
I: 0 -> MS1: T1 prio 5
I: 0 -> MS2: T1 prio 5
I: 0 ---> L2: T1 prio 5
I: 0 -> T1: prio after 5
I: N -> S1: T1 prio 5
I: 0 -> S1: T1 prio 5
I: --------------
I: 1 -> T1: prio before 5
I: 1 ---> L1: T1 prio 5
I: 1 -> MS1: T1 prio 5
I: 1 -> MS2: T1 prio 5
I: 1 ---> L2: T1 prio 5
I: 1 -> T1: prio after 5
I: N -> S1: T1 prio 5
I: 1 -> S1: T1 prio 5
I: --------------
I: 2 -> T1: prio before 5
I: 2 ---> L1: T1 prio 5
I: 2 -> MS1: T1 prio 5
I: 2 ---> L2: T1 prio 5
I: 2 -> T1: prio after 5
I: 2 -> MS2: T1 prio 5
I: --------------
I: 3 -> T1: prio before 5
I: 3 ---> L1: T1 prio 5
I: 3 -> MS1: T1 prio 5
I: 3 ---> L2: T1 prio 5
I: 3 -> T1: prio after 5
I: 3 -> MS2: T1 prio 5
I: --------------
I: 4 -> T1: prio before 5
I: 4 ---> L1: T1 prio 5
I: 4 ---> L2: T1 prio 5
I: 4 -> T1: prio after 5
I: 4 -> MS2: T1 prio 5
I: --------------
I: 5 -> T1: prio before 5
I: 5 ---> L1: T1 prio 5
I: 5 ---> L2: T1 prio 5
I: 5 -> T1: prio after 5
I: 5 -> MS2: T1 prio 5
I: --------------
I: 6 -> T1: prio before 5
I: 6 ---> L1: T1 prio 5
I: 6 -> MS1: T1 prio 5
I: 6 -> MS2: T1 prio 5
I: 6 ---> L2: T1 prio 5
I: 6 -> T1: prio after 5
I: N -> S1: T1 prio 5
I: 6 -> S1: T1 prio 5
I: --------------
<continues>
Exit QEMU by pressing CTRL+A x.
The figure below illustrates the execution of the same scenario but with the priority boost enabled. The developer must enable the priority boost and properly attach all the observers to their threads.
To execute the sample with priority boost feature enabled, run the following command:
# From the root of the zephyr repository
west build -b qemu_x86 samples/subsys/zbus/priority_boost -- -DCONFIG_ZBUS_PRIORITY_BOOST=y
west build -t run
Sample Output
I: --------------
I: 0 -> T1: prio before 5
I: 0 ---> L1: T1 prio 1
I: 0 ---> L2: T1 prio 1
I: N -> S1: T1 prio 5
I: 0 -> S1: T1 prio 5
I: 0 -> MS1: T1 prio 5
I: 0 -> MS2: T1 prio 5
I: 0 -> T1: prio after 5
I: --------------
I: 1 -> T1: prio before 5
I: 1 ---> L1: T1 prio 1
I: 1 ---> L2: T1 prio 1
I: N -> S1: T1 prio 5
I: 1 -> S1: T1 prio 5
I: 1 -> MS1: T1 prio 5
I: 1 -> MS2: T1 prio 5
I: 1 -> T1: prio after 5
I: --------------
I: 2 -> T1: prio before 5
I: 2 ---> L1: T1 prio 2
I: 2 ---> L2: T1 prio 2
I: 2 -> MS1: T1 prio 5
I: 2 -> MS2: T1 prio 5
I: 2 -> T1: prio after 5
I: --------------
I: 3 -> T1: prio before 5
I: 3 ---> L1: T1 prio 2
I: 3 ---> L2: T1 prio 2
I: 3 -> MS1: T1 prio 5
I: 3 -> MS2: T1 prio 5
I: 3 -> T1: prio after 5
I: --------------
I: 4 -> T1: prio before 5
I: 4 ---> L1: T1 prio 3
I: 4 ---> L2: T1 prio 3
I: 4 -> MS2: T1 prio 5
I: 4 -> T1: prio after 5
I: --------------
I: 5 -> T1: prio before 5
I: 5 ---> L1: T1 prio 3
I: 5 ---> L2: T1 prio 3
I: 5 -> MS2: T1 prio 5
I: 5 -> T1: prio after 5
I: --------------
I: 6 -> T1: prio before 5
I: 6 ---> L1: T1 prio 1
I: 6 ---> L2: T1 prio 1
I: N -> S1: T1 prio 5
I: 6 -> S1: T1 prio 5
I: 6 -> MS1: T1 prio 5
I: 6 -> MS2: T1 prio 5
I: 6 -> T1: prio after 5
I: --------------
<continues>
Exit QEMU by pressing CTRL+A x.