On 11/24/2014 04:54 PM, Lukas Slebodnik wrote:
On (24/11/14 16:33), Michal Židek wrote:
> On 11/24/2014 12:41 PM, Pavel Březina wrote:
>> On 11/21/2014 03:52 PM, Michal Židek wrote:
>>> On 11/21/2014 03:17 PM, Pavel Březina wrote:
>>>> On 11/21/2014 03:02 PM, Michal Židek wrote:
>>>>> On 11/21/2014 12:37 PM, Pavel Březina wrote:
>>>>>> On 11/20/2014 07:22 PM, Michal Židek wrote:
>>>>>>> Hi,
>>>>>>>
>>>>>>> it is probably not very intuitive to choose the
>>>>>>> 'period' parameter as the initial interval in
>>>>>>> the backoff feature (ptask). The first_delay and
>>>>>>> enabled_delay are more suitable for this.
>>>>>>>
>>>>>>> See the attached patch.
>>>>>>>
>>>>>>> Michal
>>>>>>
>>>>>> I still don't think this is the best idea. Let's discuss
it a little.
>>>>>>
>>>>>> Can you remind me what is the purpose of the backoff feature?
Why
>>>>>> was it
>>>>>> implemented? AFAIK it was to detect when we can get back online
and
>>>>>> the
>>>>>> randomization was added to spread the load on a server.
>>>>>
>>>>> We use the ptask API to check if the remote server is still offline.
If
>>>>> it is (offline), the task is rescheduled with doubled period
(+random
>>>>> offest).
>>>>>
>>>>>>
>>>>>> I don't like the fact that in the current state the delay
parameter is
>>>>>> ignored if the backoff is set. And therefore all first delay,
enabled
>>>>>> delay and period (with your new patch) is ignored.
>>>>>
>>>>> Now I am confused a little. With the patch that I attached, the
>>>>> enabled_delay and first_delay are respected. Only the period
>>>>> is ignored (note that the enabled/first_delay are passed as the
>>>>> "delay" paramter to the be_ptask_schedule).
>>>>
>>>> Ah, that is true. Sorry.
>>>>
>>>> We should not ignore the period though. Imagine that you'll use it
for
>>>> some task where first/enabled delay differs a lot from period. Or where
>>>> first/enabled delay will be zero. We should stick to the original plan
>>>> and double the period value.
>>>
>>> Ok.
>>>
>>> The originally designed behaviour was following:
>>> - shedule execution
>>> - if the task was not disabled after last execution, schedule
>>> next execution but double the period
>>>
>>> If I understand you correctly what you propose is to change it to
>>> following:
>>> - schedule execution (with first/enabled delay)
>>> - if the task was not disabled after last execution:
>>> -schedule next execution using 'period' (if backoff_period was
0)
>>> -schedule next execution with doubled backoff_period
>>
>> Yes.
>>
>>> I thought it will be easier to understand the flow if we use
>>> one initial delay in backoff and than just double it. But your
>>> proposal makes sense. Do you want to prepare the patch or shall
>>> I do?
>>
>> New patch is attached. I removed the backoff_delay field and use period
>> directly instead. I think the flow is now pretty straight-forward and
>> clean.
>>
>>>>>> If I understand the purpose of this backoff feature correctly,
you
>>>>>> want
>>>>>> to increase the period after each execution. But in my opinion
you
>>>>>
>>>>> Yes.
>>>>>
>>>>>> should still obey the first delay and enabled delay and use the
>>>>>> *exact*
>>>>>> times (even without the random offset IMHO).
>>>>>
>>>>> We should not ignore the random_offset. That would kill the purpose.
>>>>> For example if the server goes off for less than first_delay,
>>>>> the next "online check" will be successful for all
clients
>>>>> (that is why the randomization is needed even in the first delay).
>>>>> It is why the randomization was added.
>>>>
>>>> OK.
>>>>
>>>>>
>>>>>>
>>>>>> Attached is an *untested* patch to illustrate what I have in
mind.
>
> The patch does not apply on current master. You probably forgot
> to attach some previous patch where you create the private header.
>
It might be based on top of patches "[PATCH] tests: be_ptask"
LS
Yes, sorry I did not mention that.