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

[Jerin Jacob <jerinjacobk@gmail.com>]

On Mon, Jun 15, 2020 at 5:02 PM Burakov, Anatoly
<anatoly.burakov@intel.com> wrote:
>
> 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.

Is probing "/sys/devices/system/cpu/cpu0/cpufreq/scaling_governor"
file presence,
detects the power lib availability . Right?  Not the failure. Right?
IMO, it make sense to have following case:
# first check, Is the system is capable of power lib if so use power lib
# if the system is not capable of using power lib use interrupt mode.

I think, there is difference between system capable of using power lib
vs power lib not available or power lib failure.




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