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

[Feifei Wang <Feifei.Wang2@arm.com>]

> -----邮件原件-----
> 发件人: Thomas Monjalon <thomas@monjalon.net>
> 发送时间: Friday, October 21, 2022 4:42 AM
> 收件人: David Marchand <david.marchand@redhat.com>
> 抄送: Hunt, David <david.hunt@intel.com>; Ruifeng Wang
> <Ruifeng.Wang@arm.com>; dev@dpdk.org; nd <nd@arm.com>; Feifei
> Wang <Feifei.Wang2@arm.com>
> 主题: Re: 回复: [PATCH v1 3/3] examples/l3fwd-power: enable PMD power
> mgmt on Arm
> 
> 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.

Ok, Understand. Thanks for the explanation.
> 
> > 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.

Yes, I think what we need to do is not a create a new API, it is to look
for a correct location to call 'rte_power_monitor_wakeup'. 

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