Messages in this thread | | | Date | Tue, 08 Nov 2005 11:05:48 +0800 | From | liyu <> | Subject | Re: [question] I doublt on timer interrput. |
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I get it !
I am sorry to spend your time so much, all trouble are came from one my low-level fault.
I put "++count_tick" in scheduler_tick(), but that function() can return before it!
This is one sample result:
> [root@CCOSS_629884359 root]# cat /proc/sys/kernel/count_tick > /proc/interrupts > 157491 > CPU0 > 0: 157390 IO-APIC-edge timer > 1: 10 IO-APIC-edge i8042 > 8: 1 IO-APIC-edge rtc > 9: 0 IO-APIC-level acpi > 12: 111 IO-APIC-edge i8042 > 14: 57616 IO-APIC-edge ide0 > 15: 2 IO-APIC-edge ide1 > 16: 0 IO-APIC-level uhci_hcd:usb1 > 17: 0 IO-APIC-level uhci_hcd:usb2 > 18: 893 IO-APIC-level eth0 > NMI: 0 > LOC: 157326 > ERR: 0
We can see:
157491 > 157390 !
Yeah, I got it.
Thanks a lot again.
-liyu
Fawad Lateef wrote:
>On 11/8/05, liyu <liyu@ccoss.com.cn> wrote: > > >>Fawad Lateef Wrote: >> >> >> >>>What I found in the kernel code is that scheduler_tick is called from >>>two locations in the kernel (2.6.14-mm1) code (i386). >>> >>>1) from kernel/timer.c in update_process_times which is called from >>>arch/i386/kernel/apic.c and its calling depends on the CONFIG_SMP >>>defined or not (see >>>http://sosdg.org/~coywolf/lxr/source/arch/i386/kernel/apic.c#L1160) >>>and as you don't have CONFIG_SMP enabled so its won't be called from >>>here. >>> >>>2) from sched_fork function in kernel/sched.c >>>(http://sosdg.org/~coywolf/lxr/source/kernel/sched.c#L1414) and I >>>think its called when newly forked process setup is going to be >>>performed, and I think as from here scheduler_tick is called in your >>>case, so you are getting different value for your variable tick_count >>> >>>scheduler_tick might be called from somewhere else which I am missing >>>so please CMIIW ! >>> >>> >>> >>Please see this URL: >> >>http://lxr.linux.no/source/include/asm-i386/mach-default/do_timer.h#L20 >> >>static inline void do_timer_interrupt_hook(struct pt_regs *regs) >>{ >> do_timer(regs); >>#ifndef CONFIG_SMP >> update_process_times(user_mode(regs)); >>#endif >>/* >> * In the SMP case we use the local APIC timer interrupt to do the >> * profiling, except when we simulate SMP mode on a uniprocessor >> * system, in that case we have to call the local interrupt handler. >> */ >>#ifndef CONFIG_X86_LOCAL_APIC >> profile_tick(CPU_PROFILING, regs); >>#else >> if (!using_apic_timer) >> smp_local_timer_interrupt(regs); >>#endif >>} >> >> >>That is the code in 2.6.12, but 2.6.13.3 also same with it at least. >>So we call scheduler_tick() HZ times per second, both enable >>SMP or disable it. >> >> >> > >Yes, this is the thing which I missed > > > > >>Nod, I agree with your words, the scheduler_tick() do not same with >>timer interrupt handler on call times. but I guess it should be more >>than jiffies, beacause of other functions also can call it (for example, >>as Lateef said, sched_fork().) >> >>I think that >> >>scheduler_tick() might be called from somewhere >> >>is not exact. >> >>We may note, it do not be EXPORT_SYMBOL_*()ed , so it only can be called >>from kernel core, >>not kernel modules. Such a few places we can find it use LXR or grep. >> >> >> > >By saying __might_be_called_from_somewhere__ I meant that I am missing >some-other place __with-in_the_kernel_code__ from where it is called, >which you pointed to me (about do_timer.h) :) > > > >>I use setup one sysctl integer variable to watch the value of 'count_tick', >>Do this way have any problem? I found some value skips, but I think it is >>normal case. >> >> >> > >If you are declaring count_tick as a global variable (without static) >in sched.c then you can just use it in your test module by specifying >extern for your variable > > > >>However, I will make a experiemnt that write one hook like do_timer(), >>as Love said >> >>PS: if our scheduler_tick() is not called every timer interrput, the >>compute of task timeslice >>also is not exact ?! >> >> >> > >Yes, I am now sure that it will be called for every timer interrupt ! :) > >Thanks, > >-- >Fawad Lateef > > > >
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