[PATCH 1/3] log: Add log_check_level function

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Jacob Erlbeck jerlbeck at sysmocom.de
Mon Dec 21 15:23:11 UTC 2015


On 21.12.2015 15:52, Holger Freyther wrote:
> 
>> On 21 Dec 2015, at 15:13, Jacob Erlbeck <jerlbeck at sysmocom.de> wrote:
>>
>> Hi Holger,
>>
>> On 21.12.2015 14:17, Holger Freyther wrote:
>>>
>>>> On 17 Nov 2015, at 11:52, Jacob Erlbeck <jerlbeck at sysmocom.de> wrote:
>>
>>>> +		/* This might get logged (ignoring filters) */
>>>
>>> What is the reasoning for this part?
>>
>> I wanted to have a weaker criterion than 'return true if and only if
>> something would be logged' to be more flexible when it comes to
>> optimization. I had lookup tables in mind which cache the max level per
>> facility, and which get updated when e.g. log_set_log_level is called.
>> This would be O(1) consuming just a few CPU cycles per log, but would
>> not help when filtering is used.
>>
>> And I didn't really understand filters when I wrote that commit.
>> Including them into the log_check_level decision definitely makes sense
>> if I want to use log DEBUG level stuff on an embedded or high load system.
> 
> Okay maybe I am missing a case here but it feels like we don't save anything
> by not calling it. So if the log level is good for output we return 1 and then do
> the full work. It doesn't really matter which function we do this work in.
> 
> And as this doesn't matter we can leave it out. I posted a patch that removes
> the selection criteria and subsys code clone.

Hmm, there seems to be some misunderstanding. While thinking about the
filter stuff again, I liked the idea to include the filter test into
log_check_level. It would made it possible to DEBUG-log e.g. single
subscribers or MS without rendering the application unusable if the load
were high (and filters really supported). So please don't remove it from
your patch.

Jacob

-- 
- Jacob Erlbeck <jerlbeck at sysmocom.de>       http://www.sysmocom.de/
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