Re: [PATCH] ath10k: add configurable debugging.

[Adrian Chadd <adrian@freebsd.org>]

On 31 May 2017 at 14:28, Arend van Spriel <arend.vanspriel@broadcom.com> wrote:
> On 31-05-17 22:23, Adrian Chadd wrote:
>> On 31 May 2017 at 13:20, Arend van Spriel <arend.vanspriel@broadcom.com> wrote:
>>> On 31-05-17 14:16, Kalle Valo wrote:
>>>> Adrian Chadd <adrian@freebsd.org> writes:
>>>>
>>>>> This adds a few configurable debugging options:
>>>>>
>>>>> * driver debugging and tracing is now configurable per device
>>>>> * driver debugging and tracing is now configurable at runtime
>>>>> * the debugging / tracing is not run at all (besides a mask check)
>>>>>   unless the specific debugging bitmap field is configured.
>>>>>
>>>>> Signed-off-by: Adrian Chadd <adrian@FreeBSD.org>
>>>>
>>>> [...]
>>>>
>>>>> --- a/drivers/net/wireless/ath/ath10k/core.c
>>>>> +++ b/drivers/net/wireless/ath/ath10k/core.c
>>>>> @@ -2444,6 +2444,8 @@ struct ath10k *ath10k_core_create(size_t priv_size, struct device *dev,
>>>>>      ar->hw_rev = hw_rev;
>>>>>      ar->hif.ops = hif_ops;
>>>>>      ar->hif.bus = bus;
>>>>> +    ar->debug_mask = ath10k_debug_mask;
>>>>> +    ar->trace_debug_mask = ath10k_debug_mask;
>>>>
>>>> Until now tracing has been always enabled, irrespective what debug_mask
>>>> has contained. Now you are changing that and by default log messages are
>>>> not delivered through tracing until user enables them. So I think to
>>>> keep the old behaviour trace_debug_mask should be ATH10K_DBG_ANY
>>>> (0xffffffff) by default and the user can modify the mask per device via
>>>> the debugfs file.
>>>>
>>>> But is it really needed to be able to filter trace messages? debug_mask
>>>> I understand, but not sure about trace_debug_mask.
>>>
>>> FWIW, in brcmfmac I decided not to filter trace messages. The overhead
>>> is relatively small and if needed you can pass filter expressions with
>>> trace-cmd record.
>>
>> The reason for configuring it via a mask is that:
>>
>> * the previous behaviour is "always call debug(), conditionally print,
>> always pass to trace"
>>
>> This meant that function arguments were evaluated even if things
>> weren't being printed.
>>
>> So to avoid that in the default case, there are now two masks. If I
>> have one mask then I can only trace what is being printed, which is
>> not desired. I'd like to be able to have no overhead when doing no
>> debugging, a little overhead when doing tracing (and only the items
>> being traced), and then printing when I want to print.
>
> Well, it is up to you. Have to clariy though that if you are not
> actually recording a trace there is (almost) no overhead. We have
> Kconfig to compile tracing code in and I see no performance impact with
> tracing code. Only when doing tracing you will get little overhead.

The tracing mask is only there to avoid calling debug() all the time
for events that aren't being debugged. That definitely has a cost.



-adrian