[PATCH net 1/1] net: fec: update dirty_tx even if no skb

Fugang Duan fugang.duan at nxp.com
Sun Apr 24 18:57:45 PDT 2016


From: Troy Kisky <troy.kisky at boundarydevices.com> Sent: Saturday, April 23, 2016 12:12 AM
> To: Fugang Duan <fugang.duan at nxp.com>; netdev at vger.kernel.org;
> davem at davemloft.net; lznuaa at gmail.com
> Cc: Fabio Estevam <fabio.estevam at nxp.com>; l.stach at pengutronix.de;
> andrew at lunn.ch; tremyfr at gmail.com; gerg at uclinux.org; linux-arm-
> kernel at lists.infradead.org; johannes at sipsolutions.net;
> stillcompiling at gmail.com; sergei.shtylyov at cogentembedded.com;
> arnd at arndb.de; holgerschurig at gmail.com
> Subject: Re: [PATCH net 1/1] net: fec: update dirty_tx even if no skb
> 
> On 4/21/2016 10:59 PM, Fugang Duan wrote:
> > From: Troy Kisky <troy.kisky at boundarydevices.com> Sent: Friday, April
> > 22, 2016 10:01 AM
> >> To: netdev at vger.kernel.org; davem at davemloft.net; Fugang Duan
> >> <fugang.duan at nxp.com>; lznuaa at gmail.com
> >> Cc: Fabio Estevam <fabio.estevam at nxp.com>; l.stach at pengutronix.de;
> >> andrew at lunn.ch; tremyfr at gmail.com; gerg at uclinux.org; linux-arm-
> >> kernel at lists.infradead.org; johannes at sipsolutions.net;
> >> stillcompiling at gmail.com; sergei.shtylyov at cogentembedded.com;
> >> arnd at arndb.de; holgerschurig at gmail.com; Troy Kisky
> >> <troy.kisky at boundarydevices.com>
> >> Subject: [PATCH net 1/1] net: fec: update dirty_tx even if no skb
> >>
> >> If dirty_tx isn't updated, then dma_unmap_single will be called twice.
> >>
> >> This fixes a
> >> [   58.420980] ------------[ cut here ]------------
> >> [   58.425667] WARNING: CPU: 0 PID: 377 at /home/schurig/d/mkarm/linux-
> >> 4.5/lib/dma-debug.c:1096 check_unmap+0x9d0/0xab8()
> >> [   58.436405] fec 2188000.ethernet: DMA-API: device driver tries to free
> DMA
> >> memory it has not allocated [device address=0x0000000000000000]
> >> [size=66 bytes]
> >>
> >> encountered by Holger
> >>
> >> Signed-off-by: Troy Kisky <troy.kisky at boundarydevices.com>
> >> Tested-by: <holgerschurig at gmail.com>
> >> ---
> >>  drivers/net/ethernet/freescale/fec_main.c | 8 +++-----
> >>  1 file changed, 3 insertions(+), 5 deletions(-)
> >>
> >> diff --git a/drivers/net/ethernet/freescale/fec_main.c
> >> b/drivers/net/ethernet/freescale/fec_main.c
> >> index 08243c2..b71654c 100644
> >> --- a/drivers/net/ethernet/freescale/fec_main.c
> >> +++ b/drivers/net/ethernet/freescale/fec_main.c
> >> @@ -1197,10 +1197,8 @@ fec_enet_tx_queue(struct net_device *ndev,
> u16
> >> queue_id)
> >>  					 fec16_to_cpu(bdp->cbd_datlen),
> >>  					 DMA_TO_DEVICE);
> >>  		bdp->cbd_bufaddr = cpu_to_fec32(0);
> >> -		if (!skb) {
> >> -			bdp = fec_enet_get_nextdesc(bdp, &txq->bd);
> >> -			continue;
> >> -		}
> >> +		if (!skb)
> >> +			goto skb_done;
> >>
> >>  		/* Check for errors. */
> >>  		if (status & (BD_ENET_TX_HB | BD_ENET_TX_LC | @@ -1239,7
> >> +1237,7 @@ fec_enet_tx_queue(struct net_device *ndev, u16 queue_id)
> >>
> >>  		/* Free the sk buffer associated with this last transmit */
> >>  		dev_kfree_skb_any(skb);
> >> -
> >> +skb_done:
> >>  		/* Make sure the update to bdp and tx_skbuff are performed
> >>  		 * before dirty_tx
> >>  		 */
> >> --
> >> 2.5.0
> >
> > The patch is fine for me.
> > Can you review below patch that also fix the issue. It can take much
> > effort due to less rmb() and READ_ONCE() operation that is very
> > sensitive for duplex Gbps test for i.MX6SX/i.MX7d SOC. (i.MX6SX can
> > reach at 1.4Gbps, i.MX7D can reach at 1.8Gbps.)
> 
> 
> 
> If  "READ_ONCE(bdp->cbd_sc)" is really that expensive, then you should skip the
> 1st read as well and only do it after skb presence is verified. But some numbers
> would really help sell the patch.
> Also, I comment as to why the code is reorganized would be warranted
> 
I will do the performance test on i.MX7d to compare the data for the two patches.
Wait my result...

Thanks.

> 
> >
> > --- a/drivers/net/ethernet/freescale/fec_main.c
> > +++ b/drivers/net/ethernet/freescale/fec_main.c
> > @@ -1160,12 +1160,13 @@ static void
> >  fec_enet_tx_queue(struct net_device *ndev, u16 queue_id)  {
> >         struct  fec_enet_private *fep;
> > -       struct bufdesc *bdp;
> > +       struct bufdesc *bdp, *bdp_t;
> >         unsigned short status;
> >         struct  sk_buff *skb;
> >         struct fec_enet_priv_tx_q *txq;
> >         struct netdev_queue *nq;
> >         int     index = 0;
> > +       int     i, bdnum;
> >         int     entries_free;
> >
> >         fep = netdev_priv(ndev);
> > @@ -1187,20 +1188,28 @@ fec_enet_tx_queue(struct net_device *ndev,
> u16 queue_id)
> >                 if (status & BD_ENET_TX_READY)
> >                         break;
> >
> > -               index = fec_enet_get_bd_index(bdp, &txq->bd);
> > -
> > +               bdp_t = bdp;
> > +               bdnum = 1;
> > +               index = fec_enet_get_bd_index(txq->tx_bd_base, bdp_t,
> > + fep);
> >                 skb = txq->tx_skbuff[index];
> > -               txq->tx_skbuff[index] = NULL;
> > -               if (!IS_TSO_HEADER(txq, fec32_to_cpu(bdp->cbd_bufaddr)))
> > -                       dma_unmap_single(&fep->pdev->dev,
> > -                                        fec32_to_cpu(bdp->cbd_bufaddr),
> > -                                        fec16_to_cpu(bdp->cbd_datlen),
> > -                                        DMA_TO_DEVICE);
> > -               bdp->cbd_bufaddr = cpu_to_fec32(0);
> > -               if (!skb) {
> > -                       bdp = fec_enet_get_nextdesc(bdp, &txq->bd);
> > -                       continue;
> > +               while (!skb) {
> > +                       bdp_t = fec_enet_get_nextdesc(bdp_t, &txq->bd);
> > +                       index = fec_enet_get_bd_index(txq->tx_bd_base, bdp_t, fep);
> > +                       skb = txq->tx_skbuff[index];
> > +                       bdnum++;
> > +               }
> > +               status = fec16_to_cpu(READ_ONCE(bdp->cbd_sc));
> > +               if (status & BD_ENET_TX_READY)
> > +                       break;
> > +
> > +               for (i = 0; i < bdnum; i++) {
> > +                       if (!IS_TSO_HEADER(txq, bdp->cbd_bufaddr))
> > +                               dma_unmap_single(&fep->pdev->dev, bdp->cbd_bufaddr,
> > +                                                bdp->cbd_datlen, DMA_TO_DEVICE);
> > +                       bdp->cbd_bufaddr = 0;
> > +                       if (i < bdnum - 1)
> > +                               bdp = fec_enet_get_nextdesc(bdp,
> > + &txq->bd);
> >                 }
> > +               txq->tx_skbuff[index] = NULL;
> >
> >
> > Regards,
> > Andy
> >



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