Re: [question] I doublt on timer interrput.

[liyu]

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@xxxxxxxxxxxx> 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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