[dpdk-dev] [EXT] Re: [PATCH 3/3] l3fwd-power: add interrupt-only mode

[Burakov, Anatoly]

On 02-Jun-20 1:16 PM, Harman Kalra wrote:
> On Tue, Jun 02, 2020 at 03:53:07PM +0530, Harman Kalra wrote:
>> On Mon, Jun 01, 2020 at 01:50:26PM +0100, Burakov, Anatoly wrote:
>>> On 30-May-20 11:02 AM, Harman Kalra wrote:
>>>> On Fri, May 29, 2020 at 03:19:45PM +0100, Burakov, Anatoly wrote:
>>>>> External Email
>>>>>
>>>>> ----------------------------------------------------------------------
>>>>> On 29-May-20 2:19 PM, Harman Kalra wrote:
>>>>>
>>>>>>>     	if (ret < 0)
>>>>>>>     		rte_exit(EXIT_FAILURE, "Invalid L3FWD parameters\n");
>>>>>>> -	if (app_mode != APP_MODE_TELEMETRY && init_power_library())
>>>>>>> +	if (app_mode == APP_MODE_DEFAULT)
>>>>>>> +		app_mode = APP_MODE_LEGACY;
>>>>>>> +
>>>>>>> +	/* only legacy and empty poll mode rely on power library */
>>>>>>> +	if ((app_mode == APP_MODE_LEGACY || app_mode == APP_MODE_EMPTY_POLL) &&
>>>>>>> +			init_power_library())
>>>>>>>     		rte_exit(EXIT_FAILURE, "init_power_library failed\n");
>>>>>> Hi,
>>>>>>
>>>>>> Rather than just exiting from here can we have a else condition to
>>>>>> automatically enter into the "interrupt only" mode.
>>>>>> Please correct me if I am missing something.
>>>>>
>>>>> Hi,
>>>>>
>>>>> Thanks for your review. I don't think silently proceeding is a good idea. If
>>>>> the user wants interrupt-only mode, they should request it. Silently falling
>>>>> back to interrupt-only mode will create an illusion of successful
>>>>> initialization and set the wrong expectation for how the application will
>>>>> behave.
>>>>>
>>>>
>>>> Hi,
>>>>
>>>> Thanks for the explanation which even I also believe is logically perfect.
>>>>
>>>> But since l3fwd-power is an old application and has many users around
>>>> which are currently using this app in interrupt only mode without giving
>>>> an extra argument. But suddenly they will start getting failure messages with
>>>> the new patchset.
>>>>
>>>> My only intent with else condition was backward compatibility.
>>>> Or may be we can have more descriptive failure message, something like
>>>> "init_power_library failed, check manual for other modes".
>>>>
>>>> Thanks
>>>> Harman
>>>>
>>>>
>>>
>>> I think we can compormise on an informative log message suggesting to use
>>> interrupt mode. I'm not keen on reverting to previous buggy behavior :)
>>>
>> Hi
>>
>> I am not insisting to revert to previous behavior, I am just trying to
>> highlight some probable issues that many users might face as its an old
>> application.
>> Since many arm based soc might not be supporting frequency scaling, can
>> we add the following check as soon as the application starts, probe the
>> platform if it supports frequency scaling, if not automatically set the
>> mode to interrupt mode, something like:
>> if (access("/sys/devices/system/cpu/cpu0/cpufreq/scaling_governor",
>> 			F_OK))
>> 	app_mode = APP_MODE_INTERRUPT;
> 
> Sorry, no direct check in application but we can introduce a new API in
> power library:
>     bool rte_is_freq_scaling() {
> 	   return  access("/sys/devices/system/cpu/cpu0/cpufreq/scaling_governor",
> 			   F_OK);
>     }
> 
> and in the application we can use "rte_is_freq_scaling()" at the start.
> 

What you're suggesting here is effectively what you have already 
suggested: silently fall back to interrupt-only mode if power lib init 
failed. I already outlined why i don't think it's a good approach.

>>
>>
>> Thanks
>> Harman
>>
>>>>> -- 
>>>>> Thanks,
>>>>> Anatoly
>>>
>>>
>>> -- 
>>> Thanks,
>>> Anatoly


-- 
Thanks,
Anatoly