L4Re Operating System Framework
Interface and Usage Documentation
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C interface of the Scheduler kernel object, see L4::Scheduler for the C++ interface. More...

+ Collaboration diagram for Scheduler:

Data Structures

struct  l4_sched_cpu_set_t
 CPU sets. More...
 
struct  l4_sched_param_t
 Scheduler parameter set. More...
 

Typedefs

typedef struct l4_sched_cpu_set_t l4_sched_cpu_set_t
 CPU sets.
 
typedef struct l4_sched_param_t l4_sched_param_t
 Scheduler parameter set.
 

Enumerations

enum  L4_scheduler_classes { L4_SCHEDULER_CLASS_FIXED_PRIO = 1UL << 1 , L4_SCHEDULER_CLASS_WFQ = 1UL << 2 }
 Supported scheduler classes. More...
 
enum  L4_scheduler_ops { L4_SCHEDULER_INFO_OP = 0UL , L4_SCHEDULER_RUN_THREAD_OP = 1UL , L4_SCHEDULER_IDLE_TIME_OP = 2UL }
 Operations on the Scheduler object. More...
 

Functions

l4_sched_cpu_set_t l4_sched_cpu_set (l4_umword_t offset, unsigned char granularity, l4_umword_t map=1) L4_NOTHROW
 
l4_msgtag_t l4_scheduler_info (l4_cap_idx_t scheduler, l4_umword_t *cpu_max, l4_sched_cpu_set_t *cpus) L4_NOTHROW))
 Get scheduler information.
 
l4_msgtag_t l4_scheduler_info_with_classes (l4_cap_idx_t scheduler, l4_umword_t *cpu_max, l4_sched_cpu_set_t *cpus, l4_umword_t *sched_classes) L4_NOTHROW))
 Get scheduler information.
 
l4_sched_param_t l4_sched_param (unsigned prio, l4_umword_t quantum=0) L4_NOTHROW
 Construct scheduler parameter.
 
l4_msgtag_t l4_scheduler_run_thread (l4_cap_idx_t scheduler, l4_cap_idx_t thread, l4_sched_param_t const *sp) L4_NOTHROW)
 Run a thread on a Scheduler.
 
l4_msgtag_t l4_scheduler_idle_time (l4_cap_idx_t scheduler, l4_sched_cpu_set_t const *cpus, l4_kernel_clock_t *us) L4_NOTHROW)
 Query the idle time (in µs) of a CPU.
 
int l4_scheduler_is_online (l4_cap_idx_t scheduler, l4_umword_t cpu) L4_NOTHROW
 Query if a CPU is online.
 

Detailed Description

C interface of the Scheduler kernel object, see L4::Scheduler for the C++ interface.

The Scheduler interface allows a client to manage CPU resources. The API provides functions to query scheduler information, check the online state of CPUs, query CPU idle time and to start threads on defined CPU sets.

The scheduler offers a virtual device IRQ which triggers when the number of online cores changes, e.g. due to hotplug events. In contrast to hardware IRQs, this IRQ implements a limited functionality:

It depends on the platform, which hotplug events actually trigger the IRQ. Many platforms only support triggering the IRQ when a CPU core different from the boot CPU goes online.

Include File
#include <l4/sys/scheduler.h>
Scheduler object functions.

Enumeration Type Documentation

◆ L4_scheduler_classes

Supported scheduler classes.

Enumerator
L4_SCHEDULER_CLASS_FIXED_PRIO 

Fixed-priority scheduler.

L4_SCHEDULER_CLASS_WFQ 

Weighted fair queuing scheduler.

Definition at line 57 of file scheduler.h.

◆ L4_scheduler_ops

Operations on the Scheduler object.

Enumerator
L4_SCHEDULER_INFO_OP 

Query infos about the scheduler.

L4_SCHEDULER_RUN_THREAD_OP 

Run a thread on this scheduler.

L4_SCHEDULER_IDLE_TIME_OP 

Query idle time for the scheduler.

Definition at line 271 of file scheduler.h.

Function Documentation

◆ l4_sched_cpu_set()

l4_sched_cpu_set_t l4_sched_cpu_set ( l4_umword_t  offset,
unsigned char  granularity,
l4_umword_t  map = 1 
)
inline
Parameters
offsetOffset. Must be a multiple of 2^granularity.
granularityGranularity in log2 notation.
mapBitmap of CPUs, defaults to 1 in C++.
Returns
CPU set.
Examples
examples/sys/migrate/thread_migrate.cc.

Definition at line 281 of file scheduler.h.

References l4_sched_cpu_set_t::gran_offset, and l4_sched_cpu_set_t::map.

Referenced by l4_sched_param().

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◆ l4_sched_param()

l4_sched_param_t l4_sched_param ( unsigned  prio,
l4_umword_t  quantum = 0 
)
inline

Construct scheduler parameter.

The l4_sched_param_t::affinity of the returned value contains all CPUs.

Examples
examples/sys/aliens/main.c, examples/sys/migrate/thread_migrate.cc, examples/sys/singlestep/main.c, examples/sys/start-with-exc/main.c, and examples/sys/utcb-ipc/main.c.

Definition at line 291 of file scheduler.h.

References l4_sched_param_t::affinity, l4_sched_cpu_set(), l4_sched_param_t::prio, and l4_sched_param_t::quantum.

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◆ l4_scheduler_idle_time()

l4_msgtag_t l4_scheduler_idle_time ( l4_cap_idx_t  scheduler,
l4_sched_cpu_set_t const *  cpus,
l4_kernel_clock_t us 
)
inline

Query the idle time (in µs) of a CPU.

Parameters
schedulerScheduler object.
cpusSet of CPUs to query. Only the idle time of the first selected CPU in cpus.map is queried.
[out]usIdle time of queried CPU in µs.
Return values
0Success.
-L4_EINVALInvalid CPU requested in cpu set.

This function retrieves the idle time in µs of the first selected CPU in cpus.map. The idle time is the accumulated time a CPU has spent in the idle thread since its last reset. To calculate a load estimate l one has to retrieve the idle time at the beginning (i1) and the end (i2) of a known time interval t. The load is then calculated as l = 1 - (i2 - i1)/t.

The idle time is only defined for online CPUs. Reading the idle time from offline CPUs is undefined and may result in either getting -L4_EINVAL or calculating an estimated (incorrect) load of 1.

Note
The idle time statistics of remote CPUs is updated on context switch events only, hence may not be up-to-date when requested cross-CPU. To get up-to-date idle time you should use a thread running on the same CPU of which the idle time is requested.

Definition at line 405 of file scheduler.h.

References l4_utcb().

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◆ l4_scheduler_info()

l4_msgtag_t l4_scheduler_info ( l4_cap_idx_t  scheduler,
l4_umword_t cpu_max,
l4_sched_cpu_set_t cpus 
)
inline

Get scheduler information.

Parameters
schedulerScheduler object.
[out]cpu_maxMaximum number of CPUs ever available. Optional, can be NULL.
[in,out]cpuscpus.offset is first CPU of interest. cpus.granularity (see l4_sched_cpu_set_t). cpus.map Bitmap of online CPUs. Must not be NULL.
Return values
0Success.
-L4_ERANGEThe given CPU offset is larger than the maximum number of CPUs.

Definition at line 383 of file scheduler.h.

References l4_utcb().

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◆ l4_scheduler_info_with_classes()

l4_msgtag_t l4_scheduler_info_with_classes ( l4_cap_idx_t  scheduler,
l4_umword_t cpu_max,
l4_sched_cpu_set_t cpus,
l4_umword_t sched_classes 
)
inline

Get scheduler information.

Parameters
schedulerScheduler object.
[out]cpu_maxMaximum number of CPUs ever available. Optional, can be NULL.
[in,out]cpuscpus.offset is first CPU of interest. cpus.granularity (see l4_sched_cpu_set_t). cpus.map Bitmap of online CPUs. Must not be NULL.
[out]sched_classesA bitmap of available scheduling classes (see L4_scheduler_classes). Optional, can be NULL.
Return values
0Success.
-L4_ERANGEThe given CPU offset is larger than the maximum number of CPUs.

This function delivers the same information as l4_scheduler_info plus the available scheduler classes (see L4_scheduler_classes).

Definition at line 390 of file scheduler.h.

References l4_utcb().

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◆ l4_scheduler_is_online()

int l4_scheduler_is_online ( l4_cap_idx_t  scheduler,
l4_umword_t  cpu 
)
inline

Query if a CPU is online.

Parameters
schedulerScheduler object.
cpuCPU number whose online status should be queried.
Return values
trueThe CPU is online.
falseThe CPU is offline

Definition at line 412 of file scheduler.h.

References l4_utcb().

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◆ l4_scheduler_run_thread()

l4_msgtag_t l4_scheduler_run_thread ( l4_cap_idx_t  scheduler,
l4_cap_idx_t  thread,
l4_sched_param_t const *  sp 
)
inline

Run a thread on a Scheduler.

Parameters
schedulerScheduler object.
threadCapability of the thread to run.
spScheduling parameters.
Return values
0Success.
-L4_EINVALInvalid size of the scheduling parameter.

This function launches a thread on a CPU determined by the scheduling parameter sp.affinity. A thread can be intentionally stopped by migrating it on an offline or an invalid CPU. The thread is only guaranteed to run if the CPU it is migrated to is currently online.

Note
If the target CPU is currently not online, there is no guarantee that the thread will ever run, even if the CPU comes online later on.
A scheduler may impose a policy with regard to selecting CPUs. However the scheduler is required to ensure the following two properties:
  • Two threads with disjoint CPU sets must be scheduled to different CPUs.
  • Two threads with identical CPU sets selecting only a single CPU must be scheduled to the same CPU.
Examples
examples/sys/aliens/main.c, examples/sys/singlestep/main.c, examples/sys/start-with-exc/main.c, and examples/sys/utcb-ipc/main.c.

Definition at line 398 of file scheduler.h.

References l4_utcb().

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