Messages in this thread | | | Date | Tue, 8 Nov 2005 07:53:34 +0500 | From | Fawad Lateef <> | Subject | Re: [question] I doublt on timer interrput. |
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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 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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