Re: [PATCH] ath10k: add configurable debugging.

[Arend van Spriel <arend.vanspriel@broadcom.com>]

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.

Regards,
Arend

> -adrian
> 

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