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

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Date: Mon, 2 Oct 2023 14:49:11 +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 2:43 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)

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;