UMS Scheduler
A UMS scheduler thread is a regular pthread that has entered the UMS scheduling mode.
Enter UMS scheduling mode
A regular pthread is converted into a UMS scheduler thread performing a
ioctl call with IOCTL_ENTER_UMS request parameter;
in particular the enter_ums_scheduling_mode() begins with:
src/lib/src/scheduler.c
13struct enter_ums_mode_args enter_args = {
14 .flags = ENTER_UMS_SCHED
15};
16struct ums_sched_event event;
17ums_activation_t scheduler_activation;
18
19if (!scheduler_startup_info) {
20 errno = EFAULT;
21 return -1;
22}
23
24enter_args.ums_complist = scheduler_startup_info->completion_list;
25
26if (enter_ums_mode(&enter_args))
27 return -1;
where the enter_ums_mode is defined at
src/lib/src/private.h
22static __always_inline int enter_ums_mode(struct enter_ums_mode_args *args)
23{
24 return ioctl(UMS_FILENO, IOCTL_ENTER_UMS, args);
25}
After a pthread has entered UMS scheduling mode it starts an infinite loop
waiting for UMS scheduler events. All scheduling activities are passed from
kernel space through ums_sched_event events and then proxied to the
UMS ums_scheduler_entry_point_t.
src/lib/src/scheduler.c
29for (;;) {
30 if (dequeue_ums_sched_event(&event)) {
31 if (errno == EINTR) continue;
32 else return -1;
33 }
34
35 // proxies event to ums scheduler entry point
36 switch (event.type) {
37 case SCHEDULER_STARTUP:
38 scheduler_startup_info->ums_scheduler_entry_point(
39 UMS_SCHEDULER_STARTUP,
40 NULL,
41 scheduler_startup_info->scheduler_param
42 );
43 break;
44 case THREAD_YIELD:
45 scheduler_activation.context =
46 event.yield_params.context;
47
48 scheduler_startup_info->ums_scheduler_entry_point(
49 UMS_SCHEDULER_THREAD_YIELD,
50 &scheduler_activation,
51 event.yield_params.scheduler_params
52 );
53 break;
54 case THREAD_TERMINATED:
55 scheduler_activation.context =
56 event.end_params.context;
57
58 scheduler_startup_info->ums_scheduler_entry_point(
59 UMS_SCHEDULER_THREAD_END,
60 &scheduler_activation,
61 NULL
62 );
63 break;
64 default:
65 break;
66 }
67}
Execute UMS worker thread context
The execution of a worker thread context is implemented as follows:
src/lib/src/scheduler.c
72int execute_ums_thread(ums_context_t context)
73{
74 return ioctl(UMS_FILENO, IOCTL_EXEC_UMS_CTX, context);
75}