?????%20???????%20?-Linux

1
????? ??????? ?-Linux

• ??? ???
• (????? ?? ???? ?????? "?????? ?????" ???????)

2
????

• ???????? ????? ???????? ?-Linux
• ???? ???? ????? ????? ????? ??? ??? ?????

3
???? ??????

• ???????? ?????? ????? ?????? ?? ??? ?????????
  ???? ?? Linux ?????? ????? 2.5.X ?????
• ???????? ?? ???? ????? ????? ????? ???? ?????
  ???? Understanding the Linux Kernel
• ????? ???? ???????? ?? ????????? ????, ???? ????
  ?? ?? ???? ??? ?????? ??????? ?????? ??????? ???
  ?? ?????? ?????? 2.5.X
• ?????? ???????? include/linux/sched.h
  ?-kernel/sched.c
• ???? ???? ?? ??? ?? ???? ????????? ???? Ingo
  Molnar

4
????? ??????? ?-Linux (1)

• Linux ?????? ????? ??????? ???? "?? ?????" ??
  ????? ??????? ????? ??? ????? ?????? (time
  sharing)
• ????? ????? ?????? ??? ???? ??????? ????? ????
• ???? ??????? "??????", ????? ???? ????? ???????
  ????? ??????, ?? ?? ??????? ?? ??????? ?????? ??
  ?????
• Preemptive multitasking
• ??????? ????? ???????? ?"??????" ?-Linux ??????
  SCHED_OTHER
• ???? ???????? ????? ?????? ??? ????? ???
• ??? ????? ????? ??? ??????? ?????? ?? ??? ????
• ????? ????? ???????? ?? ????

5
????? ??????? ?-Linux (2)

• Linux ?????, ????? ???????? "??????", ???????
  ???-??? (real-time)
• ??????? ??????? ????? ?? ??????? ????? ??????
  ???? ??? ????? ??? ?????
• ??????? ?????? ?????????, ???? ???????? ???'
• ?????? ???-??? ??????? ????? ??-??? ???????
  ??????
• ??????? ?????? ???? ????? ???? ?? ?? ??????
  ???-??? ?????? ????? (??? TASK_RUNNING)
• ???? ?????? ???-??? ?????? ??? ????? ?????? ??
  ??????? ?????
• SCHED_FIFO ????? ????? (non-preemptive) ??
  ???????? ????? ????? ?? ???? ?????? ????? ?????
  ???? ?? ???? ????? ???? ???? ???? ?????. ?????
  ????? ???? ???????? ??????? ????? ??????? ?????
• SCHED_RR ????? ??? ???? (Round Robin) ???
  ????? ????? ????? ???? ??? ?? ???????? ???????
  ????? ??????? ?????

6
???????? ?????? (SCHED_OTHER)

• ??? ????? ????? ?"??????" (epochs)
• ??? ????? ????? ??? ??? ?????? ????? time slice
• ????? ?-time slice ???? ???? ?-runqueue ?????
  ????? ?????
• ?????? ????? ????? ??? ????? ???? ?????
  (TASK_RUNNING) ??? ??????? ?????? ????? ????? ??
  ??? ???? ???? ?-time slice ???
• ??? ?????, ?? ???????? ??????? ????? ???????
  ????? ?? ??? ????? ???? ?? ?-time slice ??? ??
  ???? ??????
• ????? ??????? ???? ?? ????? ?????? ???? ?????
  ???? ?? ?-time slice ???
• ???? ???? ????? ?????? ????? ???? ?? ??? ?????
  ????? ????? ????? time slice ???

7
????? ???????? ??????

• ???????? ?????? ????? ?????? Linux ?"? ????? ????
  ????? (????? kernel/sched.c)
• ?????? ???????? (scheduler) ?????? ?? ?????
  ?????? ??? ????? ????? ??? ????? ??????
• ???????? schedule()
• ?????? ????? ????? (??? ????? ????) ?? ?????
  ????? ?? ?????? ?????? ??? ????? (??????,
  time_slice, ???') ?????? ??????? ??? ?????
• ???????? scheduler_tick()
• ??? ??, ??? ????? ?????, ?????? ?????? ??????
• ???????? ????? ?????? ?? ?????? ?????/????
• ????? ??????? ??? ????? ???? ????? ????? ?????
• ????????? (de)activate_task()

8
????? ???

• ???? ???? ????? ??????? ?????? ???? ???? ?????
  ????
• ????? ??? ???? ????? ?????? ?????
• ?? ????? ???? ????? ????? ?????
• ?-Linux ????? ?????? ???? ?? HZ100Hz
• ???? ??? ????? ????? (??????? ????) ???? ?-Linux
  ???? ???? ????? jiffies

9
?????? ????? (1)

• ????? ?????? ??? ?????? ????? ?????? ?? ??????
  ?????? (process priority)
• ?????? ????? ????? ????? ????? ????? ????
• ??? ????? ???? - ?????? ?????
• ????? ?? ???? ?? ??????? ?????? ?????
• ???? ????? ?????? ????? ??-??? API (?????? ??????
  nice())
• ????? ????? ???? ????? ????? ??????? ??????
• ?????? "?????" ????? ????? ?????? ???? ?????
  ???????/???? ??-??? ????? ??????? ????? ?????
  ????
• ????? ????, ??????? ??? ????? ?/? (IO-BOUND)
  ??????? ??-??? ??????? ??? ????? ?????
  (CPU-BOUND) ???? ???? ?????? ?????

10
?????? ????? (2)

• ??????? ?? ????? ????? ??????
• ????? ??????? ?? 0..139 (MAX_PRIO-1)
• ???????? 0..99 (MAX_RT_PRIO-1) ??????? ???????
  ???-???
• ???????? 100..139 ??????? ???????? ??????
• ??? ?????? ????? ???? ????? ?????? ?????, ?????
• ????? ???? ????? ????-??? ?? ?????? 120
• ?????? ??????? ????? 120
• ????? ??? ??????? ?????? ?? ????? ?-120 ?????
  ?-niceness (??? nice) ?? ??????
• ???? ????? ????, ??? ?-nice ?? ??? -20 ?-19
• ?????? ????? ?????? TASK_NICE
• define TASK_NICE(p) ((p)-gtstatic_prio
  MAX_RT_PRIO 20)

11
??? ????? ?? ?-runqueue (1)

• ?-runqueue ??? ???? ?????? ?????? ?? ?? ?????
  ???????? (process descriptors) ?? ???????? ?????
  ?? ?????? ????? ?? ???? ????? ("????? ????")
• ?? runqueue (?? ?? ????) ???? ?? ??????? ?????
• nr_running ???? ???????? ?-runqueue (?? ???? ??
  ?-swapper)
• curr ????? ????? ?????? ??? ????
• idle ????? ????? ????? ?-swapper

12
??? ????? ?? ?-runqueue (2)

• active ????? ????? ???? ????????? ?? ????????
  ???????, ????? ??????? ?????? ????? (?????? ????
  TASK_RUNNING) ????? ??? ??? ???? ?????? ??????
  ???????
• ????? ????? ?????? ????? ??????? ????? ?????
  ????? ???? ?? ??? ??????? ????????
  activate_task()
• expired ????? ????? ???? ????????? ?? ????????
  ??????? ????? ????? ?? ?-time slice ???? ??????
  ???????
• expired_timestamp ??? ??? ?????? ??????
  ?-active ?-expired ?????? ???????

13
??? ????? ?? ?-runqueue (3)

• ???? ???? ???????? (struct prio_array) ???? ??
  ??????? ?????
• nr_active ???? ???????? ??????? ????? ??
• bitmap ????? ????? ????? ???? ????? ???????
  (140 ?????)
• ??? i ???? (1) ?? ?? ??????? ???? ?????? ???????
  i
• ?????? ??? ?????? ??? ?????? ?????? ???? ???????
  ????? ????? ?-active ????? ??? ???? ?????
  ?-O(1)
• queue ???? ?????? ????, ?? ????? ??? ????
  ?????? (140 ??????). ?? ????? ????? ??? ??? ????
  list_t.

14
??? ????? ?? ?-runqueue (4)
runqueue
nr_running
curr
???? ????? swapper
idle
active
prio_array_t
nr_active
expired
bitmap
queue
expired_ts
..
..
...
58
0
..
..
112
prio_array_t
1
..
..
120
1
..
..
????? ???????
15
????? ????? ??????? ?????? (1)

• ???? ????? ???? ?? ??????? ????? ??????? ??????
• policy ??? ??????? ?????? ?? ??????
• need_resched ??? ??? ?????? ???? ????? ??
  ?????
• ?????? set_tsk_need_resched ????? ?? ????
• ?????? clear_tsk_need_resched ???? ?? ????

16
????? ????? ??????? ?????? (2)

• prio ?????? ??????
• static_prio ??????? ?????? ?? ?????? ????
  ?????
• sleep_timestamp ??? ??????? ????? ????? ????
  ??????? (????? ?????? ??"? ??? ?? ?????? ??
  ?????)
• sleep_avg ??? ????? "?????" ?? ??????
• ???? ?????? ??????? ?????? ????? ?????
• time_slice ???? ???? (??????? ????) ??????
  ?????? ????? ????? ?????? (epoch) ???????

17
?????? ???????? ?-scheduler (1)

• ?????? ???????? ??? ???? ????? ?????? Linux
  ?????? ?? ????? ?????? ??? ?????
• ??? ???? ???????? schedule()
• ???? ???? ?? ?????? ??? ??? ????? ?? ???????
  ????? ????? context_switch() ????? ?????
• ???? ????? ????? ????? ?????????
• ?????? ?? ????? ???? ???? ?????? ???? ?? ?-time
  slice ??? (?????? ????? scheduler_tick())
• ?????? ?????? ????? ?????? ?????? ????? ?????
  ??????, ?? ?????? ????? ????? ????? ??? (?????
  ?????? sleep_on())
• ????? ?? ????? ?????? ?? ???? ?? ??????
  ?-runqueue ?????? ?? ?????? ??? ?? ???? ?????
  ???? (????? ??? wake_up())
• ???? ????? ????? ????? ?? ????? ?????? ??????
  ????? ???? sched_yield()

18
?????? ???????? ?-scheduler (2)

• ??? ???????? ????? ???? ?????? ?????? ??????
• ?? ????? ????? ?????? ????? ?? ???? ?????? ?????
  ????
• ????? ???? ????? ???? (direct invocation) ??????
  ??-??? ????? ?-schedule()
• ???? ???? ???????? ?????
• ???? ????? ?? ????? ???? (lazy invocation) ??-???
  ????? ??? need_resched ????? ?????? ???? ????
  ?-kernel mode ?-user mode
• ??? ???? ?????? ???? ???? ?? ???? ??"? ???? ???
  ?? ????? ?? schedule()
• ????? ???????? ????? ????? ?????? ?????, ?? ????
  ?-time slice ?? ??????, ????? scheduler_tick()
  ?????? ?? ???? need_resched ????? ??????

19
???????? schedule() (1)
prev ????? ????? ?????? ?????? (?????? ??
?????) rq ???? ?? ?-runqueue ?? ????? ??????

• prev current
• rq this_rq()
• ..
• spin_lock_irq(rq-gtlock)
• switch(prev-gtstate)
• case TASK_INTERRUPTIBLE
• if (signal_pending(prev))
• prev-gtstate TASK_RUNNING
• break
• default
• deactivate_task(prev, rq)
• case TASK_RUNNING

????? ???????
?? ????? ???? ???? ????? ???? ???? ?-runqueue
???? ??? ?? ????? ??????
20
???????? schedule() (2)

• if (!rq-gtnr_running)
• next rq-gtidle
• rq-gtexpired_timestamp 0
• goto switch_tasks
• array rq-gtactive
• if (!array-gtnr_active)
• rq-gtactive rq-gtexpired
• rq-gtexpired array
• array rq-gtactive
• rq-gtexpired_timestamp 0

?? ??? ???? ??????? ?????? ???? ?-runqueue, ?????
????? ?-swapper
?? ?? ????? ??????? ?-active array, ??????? ???
?-active ??-expired (???? ????? ?????? ????? ????)
21
???????? schedule() (3)

• idx sched_find_first_bit(array-gtbitmap)
• queue array-gtqueue idx
• next list_entry(queue-gtnext, task_t, run_list)
• switch_tasks
• clear_tsk_need_resched(prev)
• if (prev ! next)
• ..
• rq-gtcurr next
• prev context_switch(prev, next)
• ..
• spin_unlock_irq(rq-gtlock)
• else
• spin_unlock_irq(rq-gtlock)

?????? ??? ?????? ????? (next) ??? ?????? ??????
???? ?-active array ??? ??????? ?????? ?????
????? ????? ????? ?"? ????? ?-context_switch()
???? ?? ???? ?? ????? ??????? ???? ???? ??????
?-context_switch()?
????? ?????? next
22
????? ????? ?? ????? ?????

• ???????? scheduler_tick() ?????? ??? ????? ????
• ?????? ?? ????? ?????? ?? ?????? ?????? ???
  ?????
• ????? ??????? ?????? ??????? ????? ?????????
• "??? ????? ?????"
• ????? ?-time_slice, ???????
• ????? ???? ?? ??????? ??????? ????? ????? ??????
• ????? time_slice ???
• ????? ????? ??????????? ?????? ?????? ?????
  ?-expired ?? ??? ?-active
• ???? ?????? ??????? need_resched

23
????? ??????? ????? (1)

• Linux ????? ?? "??? ?????? ??????" ?? ????? ????
  sleep_avg ????? ??????
• "??? ????? ?????" ?? ?? ??? ?????? ?????
  ??????? ???? ?? ?? ??? ?????
• ??? ??? ?????? ????? ?? ?????, ??? ????? ????
  (??????? schedule())
• p-gtsleep_timestamp jiffies
• ???? ????? ???? ?????? ???? ??? ?????? ??????
  (??????? activate_task()) ?? ????? ???????
  MAX_SLEEP_AVG
• define MAX_SLEEP_AVG (2HZ)
• sleep_time jiffies p-gtsleep_timestamp
• p-gtsleep_avg sleep_time
• if (p-gtsleep_avg gt MAX_SLEEP_AVG)
• p-gtsleep_avg MAX_SLEEP_AVG

24
????? ??????? ????? (2)

• ?? ????? ???? ?? ?????? ?? ?????? ???????
  (???????? sheduler_tick()) ?? ???????? 0
• if (p-gtsleep_avg)
• p-gtsleep_avg--
• ??-?? ???? ????? ??
• ????? ???? ????? ???? ????? ?"??? ????? ?????"
  ????
• ????? ???? ?/? ???? ????? ?"??? ????? ?????" ????

25
????? ????? ?? ?????? ????? (1)

• Linux ?????? ?? ??????? ?? ?? ????? "????" ?????
  ????? ????? ?"??? ?????? ??????" ?? ??????
  sleep_avg
• ???????? ?????? ???-??? ??????? ???? ?????
• ????? ??????? ??????? ????? ????????
  effective_prio() ??? ????????? ???

prio static_prio bonus if (prio lt
MAX_RT_PRIO) prio MAX_RT_PRIO if (prio gt
MAX_PRIO - 1) prio MAX_PRIO 1
26
????? ????? ?? ?????? ????? (2)

• ????? ???? ?-bonus ?-5 ????? ????? ??? ??? ?????
  ????? ???????? ??? ??????? ???????????? ????????
  (???????) ?????? ?? ???
• ????, ?????? ??? nice 19 (?????? 139) ????? ?????
  ???? ?????? ??? nice 0 (?????? 120)
• ???? ????? ?? ????? ?? ??????? ?? ????? ?"?????
  ????" (???? ???????? ????? ?/?) ????? ?? ???????
  ?? ????? ?"????? ???" (???? ???????? ????? ?????)
• ???? ?? ????? MAX_SLEEP_AVG, ????? HZ ?????? ??
  ???? ???, ???? ???? ??? ??? "????? ?????" ?"?????
  ?????"

27
????? ????? ?? ?????? ????? (3)

• ????? ???? ?? ??????? ??????? ????? ?? ???? ?????
  ???? time slice ?? ???? ????? ???? ??????
• ????? ????? ?????? ????? ?????? ????? ???? ????
  ?? ???? ???? ?????? ?? ??????? ?????

28
????? time slice ?????? (1)

• time slice ????? ?????? ?????? TASK_TIMESLICE

define MIN_TIMESLICE (10 HZ / 1000) / 10
msec / define MAX_TIMESLICE (300 HZ /
1000) / 300 msec / define TASK_TIMESLICE(p)
\ MIN_TIMESLICE (MAX_TIMESLICE
MIN_TIMESLICE) (MAX_PRIO 1
(p)-gtstatic_prio)/39

• ?? ????? ???? ????? 10 msec ??? ???? ????
  ???????? ??????? ?????? ?? ?? ???? ?-300 msec
• ????? ??????? "?????" (120) ???? ??? ?????? 150
  msec
• ????? time slice ???? ????? ?? ??? ?? ???? ?-time
  slice ?????? ??? ????? ???????? scheduler_tick()
  ?????
• ?????, ?? ????? ???? ?????? ????? ??????? ?????
  ????? ????, ???? ????? ????? ?? ????? ?-time
  slice ??? ???? ????? ????? ????

29
????? time slice ?????? (2)

• ?????? ????? ???, ????? ??? ???? ????? ??-time
  slice ??? ????? ????? ???
• ????? ????? ??? ?? ????? ???? ??????? ??? ????
  ???? ???? ?????, ???? ????? ???
• ???? ???? ?-time slice, ?????? ????? ????? ??
  ?????? ????? ?? ???? ???? time slice ???? ?????
  ?????
• ???? ??-time slice ?? ??? ??????, ??? ????? ???,
  ??? ????..
• ????? ??????? ???????? do_fork() ?????? ?? fork()
• ???? ????? kernel/fork.c
• p-gttime_slice (current-gttime_slice 1) gtgt 1
• current-gttime_slice gtgt 1

30
??????? ????????????? (1)

• ??????? ????????????? ?????? ?-Linux ?????
  ?????? ???? ???? time slices ?????? ??????
  ???????
• ??????? ????????????? ?? ??????? ???????? ????
  ???????, ?????? shell, ????? ??????? ???'
  ?????? ?????? ??????
• ????? ?????? ??????? ????????????? ??? ????? ???
  ????? ????? ????? ?? ?????? ?????? ????? ????
  ?????? ?????? ??? ???????
• ????? ??????? ????????????? ??? ????? ????? ???
  ???????? ??-????????????? ?????? ?? ?-time slice
  ?????? ??????? "??????", ????? ?? ????? ??? ????
  ???????

31
??????? ????????????? (2)

• ??? ????? ?? ????? ??????, ????? "?? ?????" ??
  ??? ?????? ?? ???????? ?-expired
• define EXPIRED_STARVING(rq) \
• ((rq)-gtexpired_timestamp \
• (jiffies (rq)-gtexpired_timestamp gt \
• STARVATION_LIMIT ((rq)-gtnr_running 1))
• ???? ???????? ?-expired ??????? ???? ???, ??????
  ????? time slices ?????? ???????? ?????????????
  ?????? ???????
• ??? ?????? ??????????? ????? ???????? ?-runqueue,
  ?? ???? ??? ???? ??????? ?????? ?????, ??? ????
  ????
• ??? ?????? ?????? ???? ????, ???????
  ????????????? ?????? ???? ????? ?? ??? ????? ??
  ?????? ????? ????? ??????? ??????

32
??????? ????????????? (3)

• ????? ????? ???????????? ????? ??????
  TASK_INETRACTIVE
• define TASK_INTERACTIVE(p) \
• ((p)-gtprio lt (p)-gtstatic_prio DELTA(p))
• ???? DELTA(p) ????? ?????? ??????

• ????? ????? ???????????? ?? ??????? (???????) ???
  "?????" ???????? ?????? ???
• ????? ?? ??? ????? ????? ???? ????? ????? ??????
  ??????? ??????? ?? ??????

33
??????? ????????????? (4)

• ??? ????? ??????? ?????? ?? ??????, "?? ????"
  ?????? ??????? ????????????
• "?? ????" ?????? ???? ????? ??? ????? ????? ????
  ???? ??-??? ?????? ????????????
• ?????? ????? ?? nice -20 ???? ????? "????"
  ?????? ????? ?????? ??????? ?????? ?? ????? ?????
  -3 ?????? ??????? ????????????. ????? ???, ?????
  ??nice 19 ?? ???? ??? ??????? ???????????? ??
  ???? ????? ?? 7 ??????? ???????? ??? 5
• ?????? ??????? ???? ?????? ????? ????? ??
  ????-??? ?????? ????? (batch) ????? ??????
  ?????????? ?? ??????
• ??????? ??????? ??????, ????? ???????, ???'

34
???????? scheduler_tick() (1)

• ??????? ?? ?????? ??? ????? ???? ??????? ?????
  ????? ?? ???????
• ?? ??????? ?? ?????? ????????? ?????? ??? ?????
  ????? ?????? ?"? ????? ???????? ??????
• ???????? ????? ?????? schedule() ?? ?????? ??????
  ???? ?? ?-time slice ???
• ???????? ?????? ????????? enqueue_task()
  ?-dequeue_task() ?????? ?????? ?? ????? ????
  ?????? ?????? (active ?? expired)
• task_t p current
• runqueue_t rq this_rq()
• ..
• if (p-gtsleep_avg)
• p-gtsleep_avg--

????? ?-sleep_avg ?? ?????? ??????
35
???????? scheduler_tick() (2)

• if (!--p-gttime_slice)
• dequeue_task(p, rq-gtactive)
• set_tsk_need_resched(p)
• p-gtprio effective_prio(p)
• p-gttime_slice TASK_TIMESLICE(p)
• if (!TASK_INTERACTIVE(p) EXPIRED_STARVING(rq))
  
• if (!rq-gtexpired_timestamp)
• rq-gtexpired_timestamp jiffies
• enqueue_task(p, rq-gtexpired)
• else
• enqueue_task(p, rq-gtactive)

?? ?????? ?????? ???? ?? ?-time slice ?? ????,
??? ???? ??-active, ??????? ??????? ??-time slice
??? ??? ??????? ????, ?????? ?? schedule() ?????
???? ?????? ?????? ?????? ??????? ???? ?-expired,
?????? expired_timestamp
????? ??????????? ????? ?-active ???? time slice
???? ?????? ??????? ???? ??? ?????