Re: [question] I doublt on timer interrput.

[liyu <liyu@ccoss.com.cn>]

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
>
>
>  
>