MSOP_INIT_CPU(D2psm)

MSOP_INIT_CPU -- initialization when CPU is brought online

Synopsis

   void pfxinit_cpu(void)

Description

MSOP_INIT_CPU is called when a CPU is brought online, either for the first time or after being brought offline. It allows the PSM the chance to initialize any per-CPU states. On any given CPU, MSOP_INIT_CPU must be called before any other MSOP or delivery function.

Interrupts are disabled on the CPU when MSOP_INIT_CPU is called.

MSOP_INIT_CPU must initialize the following:

interrupt control system: Interrupts for any attached interrupt slots may be delivered to the CPU at this point. (See MSOP_INTR_ATTACH(D2psm).) ms_event_t events are also enabled at this point. Once events are enabled at the CPU by the core kernel (after a return from MSOP_INIT_CPU), the system will begin processing interrupts and PSM interrupt delivery functions will be called.
free-running high-resolution clock: This clock is used by MSOP_TIME_GET(D2psm). It may be one global clock or a local clock for each CPU.
heartbeat tick clock event generation: The PSM must post MSOP_EVENT_TICK_1 events (generated by clock 1) once per tick on each CPU on which MSOP_INIT_CPU has been called, until MSOP_OFFLINE_PREP(D2psm) is called. If the hardware supports it, the delivery of ticks should be staggered so all CPUs do not run their tick handlers at the same time.

The core kernel variable os_tick_period (see Intro(D4psm)) specifies the tick period for MSOP_EVENT_TICK_1 events. MSOP_EVENT_TICK_2 events should not be posted unless indicated by a MSOP_EVENT_TICK_2 call. The average period of clock ticks (both clock 1 and clock 2) must be within plus or minus 0.5% of the requested period, that is, with at most 7.5 minutes per day error. Individual ticks, however, may be posted as much as 45% of the tick period off the nominal end of period.

Many platforms do not have separate hardware sources for clock 1 and clock 2. Some have only one global time source, instead of per-CPU timers. In such cases, the PSM must emulate what is not provided in hardware.

To emulate per-CPU ticks from a single global tick, the PSM should post the current CPU's tick directly during the global tick interrupt, and distribute ticks to the other CPUs using cross-processor interrupts. This reproduces the effect of calling, for example, MSOP_XPOST(MS_CPU_ALL_BUT_ME, MS_EVENT_TICK_1).

Notes

If an operating system needs to perform some tick processing more coarsely than on a per-CPU basis, for example, global tick processing or per-CG tick processing, it can do this from the per-CPU tick events without any cross-processor traffic or bus locking. The simple algorithm for this is to pick a specific CPU to handle each coarser tick sequence, for example, CPU 0 for global processing and each SBSP for per-CG processing. During the chosen CPU's local tick, it would do both local processing and its additional coarser processing. A more advanced algorithm that balances the load across CPUs would involve having each CPU's tick handler keep a local tick count. The tick handler would then do per-group work when the current count modulo the group size is equal to this CPU's relative ID number within the group. All CPUs would have to co-ordinate to reset their counts during an online or offline procedure.

Arguments

None.

Return values

None.

Usage

Hardware applicability

All.

Version applicability

psm: 2

References

MSOP_INTR_ATTACH(D2psm), MSOP_TIME_GET(D2psm), MSOP_OFFLINE_PREP(D2psm)