Linux????

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Linux????

• xlanchen_at_2007.6.19

2
????

• Linux?????????????
• ??????????
• ????time(), ftime()??gettimeofday()
• ?????
• settimer(), alarm()
• ?????????????????????????????

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????

• ???????
• Linux???????????
• ???????????

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???

• 80x86?????,???????????????
• ????Real time clock,RTC
• ??????Time stamp counter,TSC
• ????????Programmable interval timer, PIT
• SMP??????APIC???

???? ????
?????????
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????RTC

• ??????PC???????
• ???CPU???????
• ????????????
• ????PC??,??????
• ?CMOS RAM??????????
• ??Motorala 146818
• ??IRQ8?????????,???2HZ8192??
• ????????????

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• Linux???RTC???????
• ????????/dev/rtc
• ????????????
• ????0x70?0x71??????RTC
• ???????????????????

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??????TSC

• ??80x86??????
• ?pentium???
• 64?????
• rdtsc?????????
• ???????,???????????1
• ??,????400MHz?????,TSC?2.5ns1

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• ????????????????,TSC??????????
• ??,Linux??????????????????
• calibrate_tsc
• ???????????????(?50ms)????TSC?????????
• ???????????????
• ????????????????,?????????????,???????

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????????PIT

• ???????,??????????
• ???8254 CMOS??
• ??I/O??0x400x43
• Linux?PIT???
• 100Hz
• ??IRQ0??????
• ?10ms????????,???tick

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• Linux???????,????????????CPU???
• ??calibrate_tsc()

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Tick???

• ?
• ??????
• ???????CPU????,???????????
• ??????????,???????????????
• Tick????????,??
• ???????Alpha?Intel?IA-64??1ms????tick(??1024?????)
  
• Rawhide Alpha???????(1200tick/?)

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• ?Linux?,???????????

??????????,???tick???
8254??????????
?8254??,??HZ?????
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• ?init_IRQ()??????????

??,??10ms??????tick
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Linux???????

• ????????,????????IRQ0????????,??
• ???????????,?
• ?????????????

15
????????

• Linux?????time_init()??IRQ0?????????

?irq0??irq_desc???? ???????
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???TSC,?????????????, ????????????
??????do_timer?????
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do_timer
????,??????? ???????? 32? ?497????(???0)
????????????? ??
??????
??tq_timer??,?????????????
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update_process_times
??????? CPU????? ??
????? ???????
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TIMER_BH????

• ?????????????????,?????????

?????????,?????????
????????
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???????

• ?????????????????????

???1970?1?1???0? ?????????
???????????? ????0999999
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• ??????,time_init()????????
• ??get_cmos_time()

??coms?? ????,Linux????RTC,????????xtime
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??xtime
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????

• ??????????,?????????????????
• ??????????????????????
• ?????????????????????????
• ????????????????????

24

• Linux????????
• ?????
• ????
• ?????
• ?????????
• ???????????????,??????????????????????,?????,????
  ????

25
?????

• ??????????????,????????????????
• ????
• ????512????????????

????
???????
????????????
26
????????????

• ??????timer_list??
• ??init_timer???,???????????????
• ??????
• ??add_timer?????????
• ???????????,?????????,??????????

27
????????

• ?????????????,????????,??????????
• Linux??expires??,?????????

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64, 64?????,???????????? ????? index?????????????
??????
(256),256?????,?????? ????????????? Index????????
?????
????????????? ???????????
??220-1???????? ?214?????????1??? ?64?
??226-1???????? ?220?????????1??? ?64?
??232-1???????? ?226?????????1??? ?64?
??214-1???????? ?256?????????1??? ?64?
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run_timer_list

• ????timer_bh()??run_timer_list()??????????,??
• ???????
• ????
• ??run_timer_list()

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????????

• ??schedule_timeout()????????(??????)
• ??schedule_timeout()??????????

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????????????

• time()
• ???1970?1?1???0??????
• ftime()
• ???1970?1?1???0????????????????
• ?????timeb
• gettimeofday()
• ???1970?1?1???0??????
• ???sys_gettimeofday()

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• settimer()
• ?????
• ???????????(??0,?????)
• alarm()
• ??SIGALARM??

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????????(??)

• date??????????
• ??time????
• ??ctime??????