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

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Date: Mon, 2 Oct 2023 14:54:55 +0200
From: Christian Marangi <ansuelsmth@...il.com>
To: Eric Dumazet <edumazet@...gle.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 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.

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

> 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;

-- 
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