Re: 回复: [PATCH v1 3/3] examples/l3fwd-power: enable PMD power mgmt on Arm

[Thomas Monjalon <thomas@monjalon.net>]

11/10/2022 09:56, Feifei Wang:
> David Marchand <david.marchand@redhat.com>
> > > On 25/08/2022 07:42, Feifei Wang wrote:
> > > > --- a/examples/l3fwd-power/main.c
> > > > +++ b/examples/l3fwd-power/main.c
> > > > @@ -432,8 +432,16 @@ static void
> > > >   signal_exit_now(int sigtype)
> > > >   {
> > > >
> > > > -     if (sigtype == SIGINT)
> > > > +     if (sigtype == SIGINT) {
> > > > +#if defined(RTE_ARCH_ARM64)
> > 
> > Having a arch specific behavior in the application shows that there is
> > something wrong either in the API, or in the Arm implementation of the API.
> > I don't think this is a good solution.
> > 
> > Can't we find a better alternative? By changing the API probably?
> Sorry I do not understand ' shows that there is something wrong either in the API'

David means the application developer should not have to be aware
of the arch differences.
When you use an API, you don't check how it is implemented,
and you are not supposed to use #ifdef.
The API must be arch-agnostic.

> Here we call ' rte_power_monitor_wakeup' API is due to that we need to wake
> up all cores from WFE instructions in arm, and then l3fwd can exit correctly.
> 
> This is due to that arm arch is different from x86, if there is no packets received, x86's
> 'UMONITOR' can automatically exit from energy-saving state after waiting for a period of time.
> But arm's 'WFE' can not exit automatically. It will wait 'SEV' instructions in wake_up API to wake
> up it.
> 
> Finally, if user want to exit l3fwd by  'SIGINT' in arm, main core should firstly call 'wake_up' API
> to force worker cores to exit from energy-saving state. 
> Otherwise, the worker will stay in the energy-saving state forever if no packet is received.

Please find a way to have a common API,
even if the API implementation is empty in x86 case.

> > 
> > 
> > > > +     /**
> > > > +      * wake_up api does not need input parameter on Arm,
> > > > +      * so 0 is meaningless here.
> > > > +      */
> > > > +             rte_power_monitor_wakeup(0); #endif
> > > >               quit_signal = true;
> > > > +     }