Task Type (TT) is an alternative CPU Scheduler for linux.
The goal of the Task Type (TT) scheduler is to detect tasks types based on their behaviours and control the schedulling based on their types. There are 5 types:
Find the descriptions and the detection rules in tasks.ods
The benefit of task types is to allow the scheduler to have more control and choose the best task to run next in the CPU.
TT gives RT tasks a -20
prio in vruntime calculations. This boosts RT
tasks over other tasks. The preemption rules are purely HRRN where RT tasks
have a priority since their vruntimes are relatively less than other types.
The reason of using HRRN instead of hard level picking is to smooth out the
preemtions and to prevent any chance of starvation.
You need to compile with CONFIG_SCHED_DEBUG=y
. I have added a field in the
output of tasks information task_type
. See and use ttdebug.sh
.
Usage examples:
ttdebug.sh | grep -i realtime
watch -t "(ttdebug.sh | grep -i interactive)"
watch -t "(ttdebug.sh | egrep -i 'webco|firefox')"
Note: Tasks types are detected based on their behaviour, not by what it should be. So if systemd at some point acted like a REALTIME tasks and went for long sleep then the type would be REALTIME until it wakes up and get its type updated. You might see many sleeping tasks with incorrect types because at some point on booting time they acted like REALTIME, CPU_BOUND, or whatever type. Those tasks are sleeping for long time, so when they wake up their type will be INTERACITVE sine they have very hight HRRN value. So, don't worry about the type of sleeping system processes.
s
kernel.sched_tt_max_lifetime
Default is 22s. This is the tasks' maximum life time to normalize their life
time and vruntime. Similar to CacULE's cacule_max_lifetime
.
kernel.sched_tt_rt_prio
Default is -20. Range [-20, 19]. In case that tasks with types other than realtime
are starving because of realtime tasks' priorities are too high, you can soften
the priority of realtime tasks. The -20 is the highest, 19 is the least priority.
kernel.sched_tt_interactive_prio
Default is -10. Range [-20, 19].
kernel.sched_tt_cpu_bound_prio
Default is -15. Range [-20, 19].
kernel.sched_tt_batch_prio
Default is 19. Range [-20, 19].
kernel.sched_tt_balancer_opt
It can be set to 4 values:
You can change the balancer option at run time.
kernel.sched_tt_lat_sens_enabled
Default is 1. latency sensitive keeps CPUs (with no tasks) at high frequency for sometime (~1ms) in
case of incoming task during this time would run faster. It reduces latency but increases power consumption.
If Power save balancer is chosen, then this option has no effect (i.e. disabled, = 0).
kernel.sched_tt_dedicated_cpu_bound_enabled
Default is 1. This option stick a CPU bound task to its current CPU to enhance cache locality.
A CPU can only have one dedicated cpu bound task.
Telegram: https://t.me/tt_sched
Thank you
Hamad