Linux???????

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Linux???????

• ????????????
• ???(0551-3606864)
• xlanchen_at_ustc.edu.cn
• Spring 2009

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Linux?????????
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????

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

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

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

native_get_wallclock
get_wallclock
read_persistent_clock
timekeeping_init?
timekeeping_resume?
timekeeping_suspend
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??????TSC

• ?80x86?????,???CLK????
• ????????????
• ?pentium??,??80x86??????????TSC
• ??64???????????????
• ????????(CLK)???1
• ??????400MHz?????,TSC?2.5ns?1
• rdtsc?????????

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• ?Linux2.6.26?,rdtscll()?rdtscl()????TSC???

rdtscl32?
rdtscll64?
native_read_tsc
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• ??????????????PIT??,TSC??????????
• ??,Linux?????????????????CLK???(?CPU?????)
• native_calculate_cpu_khz
• ???????????????????TSC?????????
• ????????????PIT??,CALIBRATE_LATCH
• ??????????????,?????????????,???????

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????????PIT

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

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Linux???????

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

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

• Jiffies??
• ???
• Xtime??

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Jiffies??

• ??????????????tick?
• ??????1
• ??jiffies_64

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???

• ?????
• ??????clocksource
• ?????

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????? clocksource_register clocksource_list ?rat
ing??
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???tsc?????
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??pit?????
init_pit_clocksource????????
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Xtime??

• ?????????

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• ????
• 1970?1?1?(UTC)??

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Xtime???

• ?????tick????
• ??update_wall_time
• ???????xtime???????
• ???

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X86????????????
start_kernel
init_timers ???? ?? ???
hrtimers_init ?????? ?? ???
timekeeping_init Xtime?? ???
time_init
sched_clock_init ????
tick_init ???? ???
hpet_time_init
setup_pit_timer ??pit_clockevent? Clockevent?? ???
global_clock_event
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pit_clockevent
????event_handler???????
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tick_init??clockevents_register_notifier??tick_not
ifier? clockevents_chain?
notifier_call_chain?? ??clockevents_chain
tick_check_new_device
tick_setup_device
tick_setup_periodic
__raw_notifier_call_chain
tick_set_periodic_handler
raw_notifier_call_chain
??event_handler tick_handle_periodic
clockevents_do_notify
tick_periodic
clockevents_register_device
update_process_times
do_timer
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?????????

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

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?????

• ??????????????,????????????????

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

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

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????????
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????
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??
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????????delayed work
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????????schedule_timeout
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????
??delay.S
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???delay_loop
??tsc??delay_tsc
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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??????

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Thanks!

• The end.