[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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