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Message-ID: <b3bb2916-0b08-e7a7-f744-21469e32e080@intel.com> Date: Thu, 8 Dec 2022 17:20:32 -0700 From: Dave Jiang <dave.jiang@...el.com> To: epilmore@...aio.com, netdev@...r.kernel.org, dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org, ntb@...ts.linux.dev, allenbh@...il.com, jdmason@...zu.us Subject: Re: [PATCH v2] ntb_netdev: Use dev_kfree_skb_any() in interrupt context On 12/8/2022 5:06 PM, epilmore@...aio.com wrote: > From: Eric Pilmore <epilmore@...aio.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_any() function. > > Previously, these callback handlers would call the > interrupt unsafe version of dev_kfree_skb(). This has > not presented an issue on Intel IOAT DMA engines as > that driver utilizes tasklets rather than a hard > interrupt handler, like the AMD PTDMA DMA driver. > On AMD systems, a kernel WARNING message is > encountered, which is 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_any(), > 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@...aio.com> Reviewed-by: Dave Jiang <dave.jiang@...el.com> As an FYI for future. Typically you would add the patch revision change log under the "---" line just as an FYI for reviewers on what you've changed and who suggested the change. > --- i.e. v2: - Use dev_kfree_skb_any() instead of dev_kfree_skb_irq(). (DaveJ) > 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 80bdc07f2cd3..59250b7accfb 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_any(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_any(skb); > > if (ntb_transport_tx_free_entry(dev->qp) >= tx_start) { > /* Make sure anybody stopping the queue after this sees the new
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