netdev - Re: [net-next PATCH 1/3] net: introduce napi_is

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Date: Mon, 2 Oct 2023 14:56:24 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Christian Marangi <ansuelsmth@...il.com>
Cc: Vincent Whitchurch <vincent.whitchurch@...s.com>, Raju Rangoju <rajur@...lsio.com>, 
	"David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Alexandre Torgue <alexandre.torgue@...s.st.com>, Jose Abreu <joabreu@...opsys.com>, 
	Maxime Coquelin <mcoquelin.stm32@...il.com>, Ping-Ke Shih <pkshih@...ltek.com>, 
	Kalle Valo <kvalo@...nel.org>, Simon Horman <horms@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, Jiri Pirko <jiri@...nulli.us>, 
	Hangbin Liu <liuhangbin@...il.com>, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-stm32@...md-mailman.stormreply.com, 
	linux-arm-kernel@...ts.infradead.org, linux-wireless@...r.kernel.org
Subject: Re: [net-next PATCH 1/3] net: introduce napi_is_scheduled helper

On Mon, Oct 2, 2023 at 2:55 PM Christian Marangi <ansuelsmth@...il.com> wrote:
>
> On Mon, Oct 02, 2023 at 02:49:11PM +0200, Eric Dumazet wrote:
> > On Mon, Oct 2, 2023 at 2:43 PM Christian Marangi <ansuelsmth@...il.com> wrote:
> > >
> > > On Mon, Oct 02, 2023 at 02:35:22PM +0200, Eric Dumazet wrote:
> > > > On Mon, Oct 2, 2023 at 2:29 PM Christian Marangi <ansuelsmth@...il.com> wrote:
> > > >
> > > > > Ehhh the idea here was to reduce code duplication since the very same
> > > > > test will be done in stmmac. So I guess this code cleanup is a NACK and
> > > > > I have to duplicate the test in the stmmac driver.
> > > >
> > > > I simply wanted to add a comment in front of this function/helper,
> > > > advising not using it unless absolutely needed.
> > > >
> > > > Thus my question "In which context is it safe to call this helper ?"
> > > >
> > > > As long as it was private with a driver, I did not mind.
> > > >
> > > > But if made public in include/linux/netdevice.h, I would rather not
> > > > have to explain
> > > > to future users why it can be problematic.
> > >
> > > Oh ok!
> > >
> > > We have plenty of case similar to this. (example some clock API very
> > > internal that should not be used normally or regmap related)
> > >
> > > I will include some comments warning that this should not be used in
> > > normal circumstances and other warnings. If you have suggestion on what
> > > to add feel free to write them.
> > >
> > > Any clue on how to proceed with the sge driver?
> > >
> >
> > I would remove use of this helper for something with no race ?
> >
> > Feel free to submit this :
> >
> > (Alternative would be to change napi_schedule() to return a boolean)
> >
>
> Think mod napi_schedule() to return a bool would result in massive
> warning (actually error with werror) with return value not handled.
>

It should not, unless we added a __must_check

> I will submit with your Suggested-by. Ok for you?

Absolutely, thanks.

>
> > diff --git a/drivers/net/ethernet/chelsio/cxgb3/sge.c
> > b/drivers/net/ethernet/chelsio/cxgb3/sge.c
> > index 2e9a74fe0970df333226b80af8716f30865c01b7..09d0e6aa4db982e3488e0c28bed33e83453801d0
> > 100644
> > --- a/drivers/net/ethernet/chelsio/cxgb3/sge.c
> > +++ b/drivers/net/ethernet/chelsio/cxgb3/sge.c
> > @@ -2501,14 +2501,6 @@ static int napi_rx_handler(struct napi_struct
> > *napi, int budget)
> >         return work_done;
> >  }
> >
> > -/*
> > - * Returns true if the device is already scheduled for polling.
> > - */
> > -static inline int napi_is_scheduled(struct napi_struct *napi)
> > -{
> > -       return test_bit(NAPI_STATE_SCHED, &napi->state);
> > -}
> > -
> >  /**
> >   *     process_pure_responses - process pure responses from a response queue
> >   *     @adap: the adapter
> > @@ -2674,9 +2666,9 @@ static int rspq_check_napi(struct sge_qset *qs)
> >  {
> >         struct sge_rspq *q = &qs->rspq;
> >
> > -       if (!napi_is_scheduled(&qs->napi) &&
> > -           is_new_response(&q->desc[q->cidx], q)) {
> > -               napi_schedule(&qs->napi);
> > +       if (is_new_response(&q->desc[q->cidx], q) &&
> > +           napi_schedule_prep(&qs->napi)) {
> > +               __napi_schedule(&qs->napi);
> >                 return 1;
> >         }
> >         return 0;
>
> --
>         Ansuel