netdev - Re: [PATCH net-next v4 1/8] bnxt_en: add support for rx-copybreak ethtool command

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Message-ID: <CACKFLikK0p1e41sbkBt1MCL=gxoWbKNHvqzEfcaV=rBfvQjB4w@mail.gmail.com>
Date: Thu, 24 Oct 2024 21:54:50 -0700
From: Michael Chan <michael.chan@...adcom.com>
To: Taehee Yoo <ap420073@...il.com>
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Subject: Re: [PATCH net-next v4 1/8] bnxt_en: add support for rx-copybreak
 ethtool command

On Thu, Oct 24, 2024 at 9:38 AM Taehee Yoo <ap420073@...il.com> wrote:
>
> On Thu, Oct 24, 2024 at 3:41 PM Michael Chan

> > > diff --git a/drivers/net/ethernet/broadcom/bnxt/bnxt.c b/drivers/net/ethernet/broadcom/bnxt/bnxt.c
> > > index bda3742d4e32..0f5fe9ba691d 100644
> > > --- a/drivers/net/ethernet/broadcom/bnxt/bnxt.c
> > > +++ b/drivers/net/ethernet/broadcom/bnxt/bnxt.c
> >
> > > @@ -4510,7 +4513,8 @@ void bnxt_set_ring_params(struct bnxt *bp)
> > >                                   ALIGN(max(NET_SKB_PAD, XDP_PACKET_HEADROOM), 8) -
> > >                                   SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
> > >                 } else {
> > > -                       rx_size = SKB_DATA_ALIGN(BNXT_RX_COPY_THRESH + NET_IP_ALIGN);
> > > +                       rx_size = SKB_DATA_ALIGN(bp->rx_copybreak +
> > > +                                                NET_IP_ALIGN);
> >
> > When rx_copybreak is 0 or very small, rx_size will be very small and
> > will be a problem.  We need rx_size to be big enough to contain the
> > packet header, so rx_size cannot be below some minimum (256?).
> >
> > >                         rx_space = rx_size + NET_SKB_PAD +
> > >                                 SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
> > >                 }
> > > @@ -6424,8 +6428,8 @@ static int bnxt_hwrm_vnic_set_hds(struct bnxt *bp, struct bnxt_vnic_info *vnic)
> > >                                           VNIC_PLCMODES_CFG_REQ_FLAGS_HDS_IPV6);
> > >                 req->enables |=
> > >                         cpu_to_le32(VNIC_PLCMODES_CFG_REQ_ENABLES_HDS_THRESHOLD_VALID);
> > > -               req->jumbo_thresh = cpu_to_le16(bp->rx_copy_thresh);
> > > -               req->hds_threshold = cpu_to_le16(bp->rx_copy_thresh);
> > > +               req->jumbo_thresh = cpu_to_le16(bp->rx_copybreak);
> > > +               req->hds_threshold = cpu_to_le16(bp->rx_copybreak);
> >
> > Similarly, these thresholds should not go to 0 when rx_copybreak becomes small.
> >
> > >         }
> > >         req->vnic_id = cpu_to_le32(vnic->fw_vnic_id);
> > >         return hwrm_req_send(bp, req);
> >
> > > @@ -4769,7 +4813,7 @@ static int bnxt_run_loopback(struct bnxt *bp)
> > >         cpr = &rxr->bnapi->cp_ring;
> > >         if (bp->flags & BNXT_FLAG_CHIP_P5_PLUS)
> > >                 cpr = rxr->rx_cpr;
> > > -       pkt_size = min(bp->dev->mtu + ETH_HLEN, bp->rx_copy_thresh);
> > > +       pkt_size = min(bp->dev->mtu + ETH_HLEN, bp->rx_copybreak);
> >
> > The loopback test will also not work if rx_copybreak is very small.  I
> > think we should always use 256 bytes for the loopback test packet
> > size.  Thanks.
> >
> > >         skb = netdev_alloc_skb(bp->dev, pkt_size);
> > >         if (!skb)
> > >                 return -ENOMEM;
>
> I tested `ethtool -t eth0` and I checked it fails if rx-copybreak is too
> small. Sorry for missing that.
> I think we can use max(BNXT_DEFAULT_RX_COPYBREAK,
> bp->rx_copybreak) for both cases.
> I tested it, it works well.
> So I will use that if you are okay!
>

Yes, please go ahead.  I think all 3 places I commented above should
use max(BNXT_DEFAULT_RX_COPYBREAK, bp->rx_copybreak).  Thanks.

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