Change the runstate of a processor
Synopsis:
#include <sys/sysmgr.h>
int sysmgr_runstate( unsigned cpu,
int enable );
int sysmgr_runstate_dynamic( unsigned cpu,
int enable );
Arguments:
- cpu
- The index of the CPU whose state you want to change.
- enable
- Zero to offline the processor; non-zero to bring it back online.
For more details, see below.
Library:
libc
Use the -l c option to
qcc
to link against this library.
This library is usually included automatically.
Description:
The sysmgr_runstate() and sysmgr_runstate_dynamic() functions
offline or online the specified CPU as follows:
- sysmgr_runstate() manually takes a CPU offline (if enable is zero)
or brings it online (if one).
- sysmgr_runstate_dynamic() lets the kernel dynamically take a CPU on- or offline
(if enable is one), depending on the system load.
These settings work together:
| Runstate |
Dynamic runstate |
Action |
| 0 |
— |
The CPU is permanently offline |
| 1 |
0 |
The CPU is permanently online (the default) |
| 1 |
1 |
The CPU is dynamically brought on- or offline by the kernel, depending on load. |
Note:
-
In order to successfully change the state, your process must have the
PROCMGR_AID_RUNSTATE ability enabled.
For more information, see
procmgr_ability().
- These functions don't turn the power on or off for the CPU;
they tell the kernel whether or not to schedule threads on it.
If you take a CPU offline, it sits on a WFI instruction (for ARM),
or a HLT instruction (for x86).
If you want to turn the power off for an idle CPU, use
InterruptHookIdle2()
to register a callback that shuts it down.
You can use
sysmgr_runstate_burst()
to notify the kernel that it should bring CPUs online because the system is about to get busy.
Returns:
EOK on success.
If an error occurs, the function can return any value listed in the Errors section.
Errors:
- EAGAIN
- A needed resource was unavailable.
- EINVAL
- The CPU bits included invalid bits.
- ENOMEM
- There was insufficient memory to complete the operation.
- EPERM
- The calling process doesn't have the required permission of PROCMGR_AID_RUNSTATE;
see procmgr_ability().
Classification:
QNX Neutrino
| Safety: |
|
|---|
| Cancellation point |
No |
| Interrupt handler |
No |
| Signal handler |
Yes |
| Thread |
Yes |