Questions about complete

Questions about complete

[loody]

Dear all:
I know complete will wake up the process who call wait_complete.
Is there any methods I can use to measure how long from calling
complete to the process that detect done=1?
Regards,
miloody

Questions about complete

[Pavan Savoy]

On Thu, Jan 6, 2011 at 11:48 AM, loody <miloody@gmail.com> wrote:
>
> Dear all:
> I know complete will wake up the process who call wait_complete.
> Is there any methods I can use to measure how long from calling
> complete to the process that detect done=1?
> Regards,
> miloody

returned value of wait_for_completion_timeout ?

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Questions about complete

[loody]

hi:

2011/1/6 Pavan Savoy <pavan_savoy@sify.com>:
> On Thu, Jan 6, 2011 at 11:48 AM, loody <miloody@gmail.com> wrote:
>>
>> Dear all:
>> I know complete will wake up the process who call wait_complete.
>> Is there any methods I can use to measure how long from calling
>> complete to the process that detect done=1?
>> Regards,
>> miloody
>
> returned value of wait_for_completion_timeout ?
No.
I want to measure the duration of complete to the time of wake up
process who is pending on wait.
thank you.

Questions about complete

[Pavan Savoy]

On Thu, Jan 6, 2011 at 12:23 PM, loody <miloody@gmail.com> wrote:
> hi:
>
> 2011/1/6 Pavan Savoy <pavan_savoy@sify.com>:
>> On Thu, Jan 6, 2011 at 11:48 AM, loody <miloody@gmail.com> wrote:
>>>
>>> Dear all:
>>> I know complete will wake up the process who call wait_complete.
>>> Is there any methods I can use to measure how long from calling
>>> complete to the process that detect done=1?
>>> Regards,
>>> miloody
>>
>> returned value of wait_for_completion_timeout ?
> No.
> I want to measure the duration of complete to the time of wake up
> process who is pending on wait.

Ah, Ok, Got it...
I would do a copy of jiffies before the complete and do a diff for
jiffies after the
wait_for_ ...

I suppose there would be much more better/optimized way ....

> thank you.
>

Questions about complete

[loody]

hi:

2011/1/6 Pavan Savoy <pavan_savoy@sify.com>:
> On Thu, Jan 6, 2011 at 12:23 PM, loody <miloody@gmail.com> wrote:
>> hi:
>>
>> 2011/1/6 Pavan Savoy <pavan_savoy@sify.com>:
>>> On Thu, Jan 6, 2011 at 11:48 AM, loody <miloody@gmail.com> wrote:
>>>>
>>>> Dear all:
>>>> I know complete will wake up the process who call wait_complete.
>>>> Is there any methods I can use to measure how long from calling
>>>> complete to the process that detect done=1?
>>>> Regards,
>>>> miloody
>>>
>>> returned value of wait_for_completion_timeout ?
>> No.
>> I want to measure the duration of complete to the time of wake up
>> process who is pending on wait.
>
> Ah, Ok, Got it...
> I would do a copy of jiffies before the complete and do a diff for
> jiffies after the
> wait_for_ ...
>
> I suppose there would be much more better/optimized way ....
thank U :)
why I ask so is I am porting kernel to other platform right now.
and I found the time of getting complete is too long.
What I mean is
function A call wait_complete_timeout
function B complete
theoretically A will get complete and leave successfully
but my platform A will told me that before timeout the complete is not got.

Regards,
miloody

Questions about complete

[Rajat Sharma]

Hi loody,

calling complete will make the waiter process runnable but won't
necessarily switch to waiter thread and make it run. Its upto
scheduler to pick this process from run queue and execute based on its
priority value. I think there is not deterministic time in which the
waiter process will start executing.

Probably what you want to do is calibrate timeout value in
wait_for_completion_timeout. I would suggest to do a binary search
between minimum timeout value (latency by which function A calls
complete, though this process can also schedule in between) to max
value (max your application can afford).

Rajat

On Thu, Jan 6, 2011 at 1:35 PM, loody <miloody@gmail.com> wrote:
> hi:
>
> 2011/1/6 Pavan Savoy <pavan_savoy@sify.com>:
>> On Thu, Jan 6, 2011 at 12:23 PM, loody <miloody@gmail.com> wrote:
>>> hi:
>>>
>>> 2011/1/6 Pavan Savoy <pavan_savoy@sify.com>:
>>>> On Thu, Jan 6, 2011 at 11:48 AM, loody <miloody@gmail.com> wrote:
>>>>>
>>>>> Dear all:
>>>>> I know complete will wake up the process who call wait_complete.
>>>>> Is there any methods I can use to measure how long from calling
>>>>> complete to the process that detect done=1?
>>>>> Regards,
>>>>> miloody
>>>>
>>>> returned value of wait_for_completion_timeout ?
>>> No.
>>> I want to measure the duration of complete to the time of wake up
>>> process who is pending on wait.
>>
>> Ah, Ok, Got it...
>> I would do a copy of jiffies before the complete and do a diff for
>> jiffies after the
>> wait_for_ ...
>>
>> I suppose there would be much more better/optimized way ....
> thank U :)
> why I ask so is I am porting kernel to other platform right now.
> and I found the time of getting complete is too long.
> What I mean is
> function A call wait_complete_timeout
> function B complete
> theoretically A will get complete and leave successfully
> but my platform A will told me that before timeout the complete is not got.
>
> Regards,
> miloody
>
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>

Questions about complete

[loody]

hi all:

2011/1/6 Rajat Sharma <fs.rajat@gmail.com>:
> Hi loody,
>
> calling complete will make the waiter process runnable but won't
> necessarily switch to waiter thread and make it run. Its upto
> scheduler to pick this process from run queue and execute based on its
> priority value. I think there is not deterministic time in which the
> waiter process will start executing.
>
> Probably what you want to do is calibrate timeout value in
> wait_for_completion_timeout. I would suggest to do a binary search
> between minimum timeout value (latency by which function A calls
> complete, though this process can also schedule in between) to max
> value (max your application can afford).
>
> Rajat
>
> On Thu, Jan 6, 2011 at 1:35 PM, loody <miloody@gmail.com> wrote:
>> hi:
>>
>> 2011/1/6 Pavan Savoy <pavan_savoy@sify.com>:
>>> On Thu, Jan 6, 2011 at 12:23 PM, loody <miloody@gmail.com> wrote:
>>>> hi:
>>>>
>>>> 2011/1/6 Pavan Savoy <pavan_savoy@sify.com>:
>>>>> On Thu, Jan 6, 2011 at 11:48 AM, loody <miloody@gmail.com> wrote:
>>>>>>
>>>>>> Dear all:
>>>>>> I know complete will wake up the process who call wait_complete.
>>>>>> Is there any methods I can use to measure how long from calling
>>>>>> complete to the process that detect done=1?
>>>>>> Regards,
>>>>>> miloody
>>>>>
>>>>> returned value of wait_for_completion_timeout ?
>>>> No.
>>>> I want to measure the duration of complete to the time of wake up
>>>> process who is pending on wait.
>>>
>>> Ah, Ok, Got it...
>>> I would do a copy of jiffies before the complete and do a diff for
>>> jiffies after the
>>> wait_for_ ...
>>>
>>> I suppose there would be much more better/optimized way ....
>> thank U :)
>> why I ask so is I am porting kernel to other platform right now.
>> and I found the time of getting complete is too long.
>> What I mean is
>> function A call wait_complete_timeout
>> function B complete
>> theoretically A will get complete and leave successfully
>> but my platform A will told me that before timeout the complete is not got.

I doubt my problem comes from cpu timer interrupt is so often such
that when function B get the change to complete, the left time is
almost exhausted.
for not to be confused, I take following jiffies for example:
1               2            3            4            5
6            8
start wait                                      B try complete
       time out

B try to complete but cpu timer keep firing and at 8 it is time out.
My platform is mips and is there any possibility to only let cpu timer
be preemptible?

BTW, in x86 or other ARCH, will they try to let timer ISR be preemptible?


-- 
Regards,
miloody

Questions about complete

[Rajat Sharma]

> B try to complete but cpu timer keep firing and at 8 it is time out.
> My platform is mips and is there any possibility to only let cpu timer
> be preemptible?
>

This seems really strange because when B calls complete, it sets up
condition variable value i.e. completion->done++ by disabling the
local interrupts. Following is code snippet from complete function:

        spin_lock_irqsave(&x->wait.lock, flags);
                   // This will disable interrupts
        x->done++;
                            // signals completion
        __wake_up_common(&x->wait, TASK_NORMAL, 1, 0, NULL);
        spin_unlock_irqrestore(&x->wait.lock, flags);

So now even if process A does not get a chance to execute and
completion timeout occurs before that, as you have shown in your
example, process A would still correctly knows about completion
because x->done was already set. Pleas look at the code snippet for
do_wait_for_common called from wait_for_completion_timeout:

          if (!x->done) {
                 ....
                 do {
                          ....
                 } while (!x->done && timeout);
                __remove_wait_queue(&x->wait, &wait);
                if (!x->done)
                        return timeout;
        }
        x->done--;
        return timeout ?: 1;

>From above code, even if timeout expires i.e. timeout=0 and x->done is
already set, this function will still return 1.

> BTW, in x86 or other ARCH, will they try to let timer ISR be preemptible?

completion functions taking spin_lock_irqsave, so timer ISR should not
preempt the complete API.

Rajat

On Fri, Jan 7, 2011 at 7:51 PM, loody <miloody@gmail.com> wrote:
>
> hi all:
>
> 2011/1/6 Rajat Sharma <fs.rajat@gmail.com>:
> > Hi loody,
> >
> > calling complete will make the waiter process runnable but won't
> > necessarily switch to waiter thread and make it run. Its upto
> > scheduler to pick this process from run queue and execute based on its
> > priority value. I think there is not deterministic time in which the
> > waiter process will start executing.
> >
> > Probably what you want to do is calibrate timeout value in
> > wait_for_completion_timeout. I would suggest to do a binary search
> > between minimum timeout value (latency by which function A calls
> > complete, though this process can also schedule in between) to max
> > value (max your application can afford).
> >
> > Rajat
> >
> > On Thu, Jan 6, 2011 at 1:35 PM, loody <miloody@gmail.com> wrote:
> >> hi:
> >>
> >> 2011/1/6 Pavan Savoy <pavan_savoy@sify.com>:
> >>> On Thu, Jan 6, 2011 at 12:23 PM, loody <miloody@gmail.com> wrote:
> >>>> hi:
> >>>>
> >>>> 2011/1/6 Pavan Savoy <pavan_savoy@sify.com>:
> >>>>> On Thu, Jan 6, 2011 at 11:48 AM, loody <miloody@gmail.com> wrote:
> >>>>>>
> >>>>>> Dear all:
> >>>>>> I know complete will wake up the process who call wait_complete.
> >>>>>> Is there any methods I can use to measure how long from calling
> >>>>>> complete to the process that detect done=1?
> >>>>>> Regards,
> >>>>>> miloody
> >>>>>
> >>>>> returned value of wait_for_completion_timeout ?
> >>>> No.
> >>>> I want to measure the duration of complete to the time of wake up
> >>>> process who is pending on wait.
> >>>
> >>> Ah, Ok, Got it...
> >>> I would do a copy of jiffies before the complete and do a diff for
> >>> jiffies after the
> >>> wait_for_ ...
> >>>
> >>> I suppose there would be much more better/optimized way ....
> >> thank U :)
> >> why I ask so is I am porting kernel to other platform right now.
> >> and I found the time of getting complete is too long.
> >> What I mean is
> >> function A call wait_complete_timeout
> >> function B complete
> >> theoretically A will get complete and leave successfully
> >> but my platform A will told me that before timeout the complete is not got.
>
> I doubt my problem comes from cpu timer interrupt is so often such
> that when function B get the change to complete, the left time is
> almost exhausted.
> for not to be confused, I take following jiffies for example:
> 1 ? ? ? ? ? ? ? 2 ? ? ? ? ? ?3 ? ? ? ? ? ?4 ? ? ? ? ? ?5
> 6 ? ? ? ? ? ?8
> start wait ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?B try complete
> ? ? ? time out
>
> B try to complete but cpu timer keep firing and at 8 it is time out.
> My platform is mips and is there any possibility to only let cpu timer
> be preemptible?
>
> BTW, in x86 or other ARCH, will they try to let timer ISR be preemptible?
>
>
> --
> Regards,
> miloody
>
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies