From: Dave Jiang <dave.jiang@intel.com>
To: epilmore@gigaio.com, netdev@vger.kernel.org,
dmaengine@vger.kernel.org, linux-kernel@vger.kernel.org,
ntb@lists.linux.dev, allenbh@gmail.com, jdmason@kudzu.us
Subject: Re: [PATCH] ntb_netdev: Use dev_kfree_skb_irq() in interrupt context
Date: Thu, 8 Dec 2022 08:35:08 -0700 [thread overview]
Message-ID: <dfd8dd16-64ed-33ef-7dd3-5c501ce99cff@intel.com> (raw)
In-Reply-To: <63914879.CJDc0NszG7y0lmQT%epilmore@gigaio.com>
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
prev parent reply other threads:[~2022-12-08 15:35 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-08 2:14 [PATCH] ntb_netdev: Use dev_kfree_skb_irq() in interrupt context epilmore
2022-12-08 15:35 ` Dave Jiang [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=dfd8dd16-64ed-33ef-7dd3-5c501ce99cff@intel.com \
--to=dave.jiang@intel.com \
--cc=allenbh@gmail.com \
--cc=dmaengine@vger.kernel.org \
--cc=epilmore@gigaio.com \
--cc=jdmason@kudzu.us \
--cc=linux-kernel@vger.kernel.org \
--cc=netdev@vger.kernel.org \
--cc=ntb@lists.linux.dev \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).