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Message-ID: <CAF=yD-LSgCEnL_kTH44A8-FH3nut3y=bonf4Bgf75=jd=D64hw@mail.gmail.com>
Date: Thu, 13 Sep 2018 11:20:06 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Jason Wang <jasowang@...hat.com>
Cc: "Michael S. Tsirkin" <mst@...hat.com>,
David Miller <davem@...emloft.net>,
virtualization@...ts.linux-foundation.org,
Network Development <netdev@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>,
Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net-next V2] virtio_net: ethtool tx napi configuration
On Thu, Sep 13, 2018 at 1:40 AM Jason Wang <jasowang@...hat.com> wrote:
>
> Implement ethtool .set_coalesce (-C) and .get_coalesce (-c) handlers.
> Interrupt moderation is currently not supported, so these accept and
> display the default settings of 0 usec and 1 frame.
>
> Toggle tx napi through a bit in tx-frames. So as to not interfere
> with possible future interrupt moderation, value 1 means tx napi while
> value 0 means not.
>
> To properly synchronize with the data path, tx napi is disabled and
> tx lock is held when changing the value of napi weight. And two more
> places that can access tx napi weight:
>
> - speculative tx polling in rx napi, we can leave it as is since it
> not a must for correctness.
> - skb_xmit_done(), one more check of napi weight is added before
> trying to enable tx to avoid tx to be disabled forever if napi is
> disabled after skb_xmit_done() but before the napi
>
> Link: https://patchwork.ozlabs.org/patch/948149/
> Suggested-by: Jason Wang <jasowang@...hat.com>
> Signed-off-by: Willem de Bruijn <willemb@...gle.com>
> Signed-off-by: Jason Wang <jasowang@...hat.com>
> ---
> Changes from V1:
> - try to synchronize with datapath to allow changing mode when
> interface is up.
> - use tx-frames 0 as to disable tx napi while tx-frames 1 to enable tx napi
> ---
> drivers/net/virtio_net.c | 64 +++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 63 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 765920905226..6e70864f5899 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -66,6 +66,8 @@ DECLARE_EWMA(pkt_len, 0, 64)
>
> #define VIRTNET_DRIVER_VERSION "1.0.0"
>
> +static const u32 ethtool_coalesce_napi_mask = (1UL << 10);
> +
This is no longer needed
> static const unsigned long guest_offloads[] = {
> VIRTIO_NET_F_GUEST_TSO4,
> VIRTIO_NET_F_GUEST_TSO6,
> @@ -1444,7 +1446,10 @@ static int virtnet_poll_tx(struct napi_struct *napi, int budget)
>
> virtqueue_napi_complete(napi, sq->vq, 0);
>
> - if (sq->vq->num_free >= 2 + MAX_SKB_FRAGS)
> + /* Check napi.weight to avoid tx stall since it could be set
> + * to zero by ethtool after skb_xmit_done().
> + */
> + if (sq->vq->num_free >= 2 + MAX_SKB_FRAGS || !sq->napi.weight)
> netif_tx_wake_queue(txq);
I see. This assumes that the napi handler will always be called on
conversion from napi to no-napi mode.
That is safe to assume because if it isn't called (and will not call
netif_tx_wake_queue) that implies that napi was not scheduled, and
thus the tx interrupt was not suppressed and thus there was no tx
completion work to be scheduled?
>
> return 0;
> @@ -2181,6 +2186,61 @@ static int virtnet_get_link_ksettings(struct net_device *dev,
> return 0;
> }
>
> +static int virtnet_set_coalesce(struct net_device *dev,
> + struct ethtool_coalesce *ec)
> +{
> + struct ethtool_coalesce ec_default = {
> + .cmd = ETHTOOL_SCOALESCE,
> + .rx_max_coalesced_frames = 1,
> + };
> + struct virtnet_info *vi = netdev_priv(dev);
> + int i, napi_weight;
> +
> + if (ec->tx_max_coalesced_frames > 1)
> + return -EINVAL;
> +
> + ec_default.tx_max_coalesced_frames = ec->tx_max_coalesced_frames;
> + napi_weight = ec->tx_max_coalesced_frames ? NAPI_POLL_WEIGHT : 0;
> +
> + /* disallow changes to fields not explicitly tested above */
> + if (memcmp(ec, &ec_default, sizeof(ec_default)))
> + return -EINVAL;
> +
> + if (napi_weight ^ vi->sq[0].napi.weight) {
> + for (i = 0; i < vi->max_queue_pairs; i++) {
> + struct netdev_queue *txq =
> + netdev_get_tx_queue(vi->dev, i);
> +
> + virtnet_napi_tx_disable(&vi->sq[i].napi);
> + __netif_tx_lock_bh(txq);
> + vi->sq[i].napi.weight = napi_weight;
> + __netif_tx_unlock_bh(txq);
> + virtnet_napi_tx_enable(vi, vi->sq[i].vq,
> + &vi->sq[i].napi);
> + }
> + }
> +
> + return 0;
> +}
> +
> +static int virtnet_get_coalesce(struct net_device *dev,
> + struct ethtool_coalesce *ec)
> +{
> + struct ethtool_coalesce ec_default = {
> + .cmd = ETHTOOL_GCOALESCE,
> + .rx_max_coalesced_frames = 1,
> + .tx_max_coalesced_frames = 0,
no need to explicitly initialize to 0 (unless you did this for
documentation purposes, which is fine).
> + };
> + struct virtnet_info *vi = netdev_priv(dev);
> +
> + memcpy(ec, &ec_default, sizeof(ec_default));
> +
> + if (vi->sq[0].napi.weight)
> + ec->tx_max_coalesced_frames = 1;
> +
> + return 0;
> +}
> +
> static void virtnet_init_settings(struct net_device *dev)
> {
> struct virtnet_info *vi = netdev_priv(dev);
> @@ -2219,6 +2279,8 @@ static const struct ethtool_ops virtnet_ethtool_ops = {
> .get_ts_info = ethtool_op_get_ts_info,
> .get_link_ksettings = virtnet_get_link_ksettings,
> .set_link_ksettings = virtnet_set_link_ksettings,
> + .set_coalesce = virtnet_set_coalesce,
> + .get_coalesce = virtnet_get_coalesce,
> };
>
> static void virtnet_freeze_down(struct virtio_device *vdev)
> --
> 2.17.1
>
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