mirror of
https://github.com/edk2-porting/linux-next.git
synced 2024-12-28 15:13:55 +08:00
60 lines
1.7 KiB
Plaintext
60 lines
1.7 KiB
Plaintext
|
|
||
|
|
|
||
|
|
Real-Time group scheduling.
|
||
|
|
|
||
|
|
The problem space:
|
||
|
|
|
||
|
|
In order to schedule multiple groups of realtime tasks each group must
|
||
|
|
be assigned a fixed portion of the CPU time available. Without a minimum
|
||
|
|
guarantee a realtime group can obviously fall short. A fuzzy upper limit
|
||
|
|
is of no use since it cannot be relied upon. Which leaves us with just
|
||
|
|
the single fixed portion.
|
||
|
|
|
||
|
|
CPU time is divided by means of specifying how much time can be spent
|
||
|
|
running in a given period. Say a frame fixed realtime renderer must
|
||
|
|
deliver 25 frames a second, which yields a period of 0.04s. Now say
|
||
|
|
it will also have to play some music and respond to input, leaving it
|
||
|
|
with around 80% for the graphics. We can then give this group a runtime
|
||
|
|
of 0.8 * 0.04s = 0.032s.
|
||
|
|
|
||
|
|
This way the graphics group will have a 0.04s period with a 0.032s runtime
|
||
|
|
limit.
|
||
|
|
|
||
|
|
Now if the audio thread needs to refill the DMA buffer every 0.005s, but
|
||
|
|
needs only about 3% CPU time to do so, it can do with a 0.03 * 0.005s
|
||
|
|
= 0.00015s.
|
||
|
|
|
||
|
|
|
||
|
|
The Interface:
|
||
|
|
|
||
|
|
system wide:
|
||
|
|
|
||
|
|
/proc/sys/kernel/sched_rt_period_ms
|
||
|
|
/proc/sys/kernel/sched_rt_runtime_us
|
||
|
|
|
||
|
|
CONFIG_FAIR_USER_SCHED
|
||
|
|
|
||
|
|
/sys/kernel/uids/<uid>/cpu_rt_runtime_us
|
||
|
|
|
||
|
|
or
|
||
|
|
|
||
|
|
CONFIG_FAIR_CGROUP_SCHED
|
||
|
|
|
||
|
|
/cgroup/<cgroup>/cpu.rt_runtime_us
|
||
|
|
|
||
|
|
[ time is specified in us because the interface is s32; this gives an
|
||
|
|
operating range of ~35m to 1us ]
|
||
|
|
|
||
|
|
The period takes values in [ 1, INT_MAX ], runtime in [ -1, INT_MAX - 1 ].
|
||
|
|
|
||
|
|
A runtime of -1 specifies runtime == period, ie. no limit.
|
||
|
|
|
||
|
|
New groups get the period from /proc/sys/kernel/sched_rt_period_us and
|
||
|
|
a runtime of 0.
|
||
|
|
|
||
|
|
Settings are constrained to:
|
||
|
|
|
||
|
|
\Sum_{i} runtime_{i} / global_period <= global_runtime / global_period
|
||
|
|
|
||
|
|
in order to keep the configuration schedulable.
|