Message ID | 63914879.CJDc0NszG7y0lmQT%epilmore@gigaio.com (mailing list archive) |
---|---|
State | Handled Elsewhere |
Headers | show |
Series | ntb_netdev: Use dev_kfree_skb_irq() in interrupt context | expand |
On 12/7/2022 7:14 PM, epilmore@gigaio.com wrote: > From: Eric Pilmore <epilmore@gigaio.com> > > TX/RX callback handlers (ntb_netdev_tx_handler(), > ntb_netdev_rx_handler()) can be called in interrupt > context via the DMA framework when the respective > DMA operations have completed. As such, any calls > by these routines to free skb's, should use the > interrupt context safe dev_kfree_skb_irq() function. > > Previously, these callback handlers would call the > interrupt unsafe version of dev_kfree_skb(). Although > this does not seem to present an issue when the > underlying DMA engine being utilized is Intel IOAT, > a kernel WARNING message was being encountered when > PTDMA DMA engine was utilized on AMD platforms. The > WARNING was being issued from skb_release_head_state() > due to in_hardirq() being true. > > Besides the user visible WARNING from the kernel, > the other symptom of this bug was that TCP/IP performance > across the ntb_netdev interface was very poor, i.e. > approximately an order of magnitude below what was > expected. With the repair to use dev_kfree_skb_irq(), > kernel WARNINGs from skb_release_head_state() ceased > and TCP/IP performance, as measured by iperf, was on > par with expected results, approximately 20 Gb/s on > AMD Milan based server. Note that this performance > is comparable with Intel based servers. > > Fixes: 765ccc7bc3d91 ("ntb_netdev: correct skb leak") > Fixes: 548c237c0a997 ("net: Add support for NTB virtual ethernet device") > Signed-off-by: Eric Pilmore <epilmore@gigaio.com> Hi Eric, Thanks for submitting this. I think the reason is ptdma runs everything in the hard interrupt handler while ioatdma runs interrupt handling in a tasklet. I just took a look at the function definitions in netdevice.h, and I think the call you want to use is dev_kfree_skb_any(). It handles being freed depending on the context for you. > --- > drivers/net/ntb_netdev.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/drivers/net/ntb_netdev.c b/drivers/net/ntb_netdev.c > index 80bdc07..283e23c 100644 > --- a/drivers/net/ntb_netdev.c > +++ b/drivers/net/ntb_netdev.c > @@ -137,7 +137,7 @@ static void ntb_netdev_rx_handler(struct ntb_transport_qp *qp, void *qp_data, > enqueue_again: > rc = ntb_transport_rx_enqueue(qp, skb, skb->data, ndev->mtu + ETH_HLEN); > if (rc) { > - dev_kfree_skb(skb); > + dev_kfree_skb_irq(skb); > ndev->stats.rx_errors++; > ndev->stats.rx_fifo_errors++; > } > @@ -192,7 +192,7 @@ static void ntb_netdev_tx_handler(struct ntb_transport_qp *qp, void *qp_data, > ndev->stats.tx_aborted_errors++; > } > > - dev_kfree_skb(skb); > + dev_kfree_skb_irq(skb); > > if (ntb_transport_tx_free_entry(dev->qp) >= tx_start) { > /* Make sure anybody stopping the queue after this sees the new
diff --git a/drivers/net/ntb_netdev.c b/drivers/net/ntb_netdev.c index 80bdc07..283e23c 100644 --- a/drivers/net/ntb_netdev.c +++ b/drivers/net/ntb_netdev.c @@ -137,7 +137,7 @@ static void ntb_netdev_rx_handler(struct ntb_transport_qp *qp, void *qp_data, enqueue_again: rc = ntb_transport_rx_enqueue(qp, skb, skb->data, ndev->mtu + ETH_HLEN); if (rc) { - dev_kfree_skb(skb); + dev_kfree_skb_irq(skb); ndev->stats.rx_errors++; ndev->stats.rx_fifo_errors++; } @@ -192,7 +192,7 @@ static void ntb_netdev_tx_handler(struct ntb_transport_qp *qp, void *qp_data, ndev->stats.tx_aborted_errors++; } - dev_kfree_skb(skb); + dev_kfree_skb_irq(skb); if (ntb_transport_tx_free_entry(dev->qp) >= tx_start) { /* Make sure anybody stopping the queue after this sees the new