netdev - Re: [PATCH net 2/4] bnxt_en: Flush XDP for bnxt_poll

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Message-ID: <ZPtlhSywT5cBTj8u@C02YVCJELVCG.dhcp.broadcom.net>
Date: Fri, 8 Sep 2023 14:18:45 -0400
From: Andy Gospodarek <andrew.gospodarek@...adcom.com>
To: Michael Chan <michael.chan@...adcom.com>
Cc: Pavan Chebbi <pavan.chebbi@...adcom.com>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	netdev@...r.kernel.org, bpf@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Jesper Dangaard Brouer <hawk@...nel.org>,
	John Fastabend <john.fastabend@...il.com>,
	Paolo Abeni <pabeni@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH net 2/4] bnxt_en: Flush XDP for bnxt_poll_nitroa0()'s NAPI

On Fri, Sep 08, 2023 at 10:57:13AM -0700, Michael Chan wrote:
> On Fri, Sep 8, 2023 at 9:30 AM Pavan Chebbi <pavan.chebbi@...adcom.com> wrote:
> >
> > On Fri, Sep 8, 2023 at 7:29 PM Sebastian Andrzej Siewior
> > <bigeasy@...utronix.de> wrote:
> > >
> > > bnxt_poll_nitroa0() invokes bnxt_rx_pkt() which can run a XDP program
> > > which in turn can return XDP_REDIRECT. bnxt_rx_pkt() is also used by
> > > __bnxt_poll_work() which flushes (xdp_do_flush()) the packets after each
> > > round. bnxt_poll_nitroa0() lacks this feature.
> > > xdp_do_flush() should be invoked before leaving the NAPI callback.
> > >
> > > Invoke xdp_do_flush() after a redirect in bnxt_poll_nitroa0() NAPI.
> > >
> > > Cc: Michael Chan <michael.chan@...adcom.com>
> > > Fixes: f18c2b77b2e4e ("bnxt_en: optimized XDP_REDIRECT support")
> > > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> > > ---
> > >  drivers/net/ethernet/broadcom/bnxt/bnxt.c | 5 +++++
> > >  1 file changed, 5 insertions(+)
> > >
> > > diff --git a/drivers/net/ethernet/broadcom/bnxt/bnxt.c b/drivers/net/ethernet/broadcom/bnxt/bnxt.c
> > > index 5cc0dbe121327..7551aa8068f8f 100644
> > > --- a/drivers/net/ethernet/broadcom/bnxt/bnxt.c
> > > +++ b/drivers/net/ethernet/broadcom/bnxt/bnxt.c
> > > @@ -2614,6 +2614,7 @@ static int bnxt_poll_nitroa0(struct napi_struct *napi, int budget)
> > >         struct rx_cmp_ext *rxcmp1;
> > >         u32 cp_cons, tmp_raw_cons;
> > >         u32 raw_cons = cpr->cp_raw_cons;
> > > +       bool flush_xdp = false;
> >
> > Michael can confirm but I don't think we need this additional variable.
> > Since the event is always ORed, we could directly check if (event &
> > BNXT_REDIRECT_EVENT) just like is done in __bnxt_poll_work().
> 
> If we have a mix of XDP_TX and XDP_REDIRECT during NAPI, event can be
> cleared by XDP_TX.  So this patch looks correct to me because of that.

Agreed

> Or we can make it consistent with __bnxt_poll_work() and assume that
> XDP_TX won't mix with XDP_REDIRECT.

Unfortunately we probably cannot guarantee that or maybe more to point
we do not want to guarantee that.

Thanks for this patch.

Reviewed-by: Andy Gospodarek <gospo@...adcom.com>


> Handling a mix of XDP actions needs to be looked at separately.  The
> driver currently won't work well when that happens.  I am working on
> an internal patch to address that and will post it when it's ready.
> Thanks.
> 
> >
> > >         u32 rx_pkts = 0;
> > >         u8 event = 0;
> > >
> > > @@ -2648,6 +2649,8 @@ static int bnxt_poll_nitroa0(struct napi_struct *napi, int budget)
> > >                                 rx_pkts++;
> > >                         else if (rc == -EBUSY)  /* partial completion */
> > >                                 break;
> > > +                       if (event & BNXT_REDIRECT_EVENT)
> > > +                               flush_xdp = true;
> > >                 } else if (unlikely(TX_CMP_TYPE(txcmp) ==
> > >                                     CMPL_BASE_TYPE_HWRM_DONE)) {
> > >                         bnxt_hwrm_handler(bp, txcmp);
> > > @@ -2667,6 +2670,8 @@ static int bnxt_poll_nitroa0(struct napi_struct *napi, int budget)
> > >
> > >         if (event & BNXT_AGG_EVENT)
> > >                 bnxt_db_write(bp, &rxr->rx_agg_db, rxr->rx_agg_prod);
> > > +       if (flush_xdp)
> > > +               xdp_do_flush();
> > >
> > >         if (!bnxt_has_work(bp, cpr) && rx_pkts < budget) {
> > >                 napi_complete_done(napi, rx_pkts);
> > > --
> > > 2.40.1
> > >
> > >