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Date: Wed, 22 Nov 2023 14:01:22 +0800
From: Jason Wang <jasowang@...hat.com>
To: Heng Qi <hengqi@...ux.alibaba.com>
Cc: netdev@...r.kernel.org, virtualization@...ts.linux-foundation.org,
mst@...hat.com, kuba@...nel.org, edumazet@...gle.com, pabeni@...hat.com,
davem@...emloft.net, hawk@...nel.org, john.fastabend@...il.com,
ast@...nel.org, horms@...nel.org, xuanzhuo@...ux.alibaba.com
Subject: Re: [PATCH net-next v4 4/4] virtio-net: support rx netdim
On Wed, Nov 22, 2023 at 1:52 PM Jason Wang <jasowang@...hat.com> wrote:
>
> On Mon, Nov 20, 2023 at 8:38 PM Heng Qi <hengqi@...ux.alibaba.com> wrote:
> >
> > By comparing the traffic information in the complete napi processes,
> > let the virtio-net driver automatically adjust the coalescing
> > moderation parameters of each receive queue.
> >
> > Signed-off-by: Heng Qi <hengqi@...ux.alibaba.com>
> > ---
> > v2->v3:
> > - Some minor modifications.
> >
> > v1->v2:
> > - Improved the judgment of dim switch conditions.
> > - Cancel the work when vq reset.
> >
> > drivers/net/virtio_net.c | 191 ++++++++++++++++++++++++++++++++++-----
> > 1 file changed, 169 insertions(+), 22 deletions(-)
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index 69fe09e99b3c..bc32d5aae005 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -19,6 +19,7 @@
> > #include <linux/average.h>
> > #include <linux/filter.h>
> > #include <linux/kernel.h>
> > +#include <linux/dim.h>
> > #include <net/route.h>
> > #include <net/xdp.h>
> > #include <net/net_failover.h>
> > @@ -172,6 +173,17 @@ struct receive_queue {
> >
> > struct virtnet_rq_stats stats;
> >
> > + /* The number of rx notifications */
> > + u16 calls;
> > +
> > + /* Is dynamic interrupt moderation enabled? */
> > + bool dim_enabled;
> > +
> > + /* Dynamic Interrupt Moderation */
> > + struct dim dim;
> > +
> > + u32 packets_in_napi;
> > +
> > struct virtnet_interrupt_coalesce intr_coal;
> >
> > /* Chain pages by the private ptr. */
> > @@ -305,6 +317,9 @@ struct virtnet_info {
> > u8 duplex;
> > u32 speed;
> >
> > + /* Is rx dynamic interrupt moderation enabled? */
> > + bool rx_dim_enabled;
> > +
> > /* Interrupt coalescing settings */
> > struct virtnet_interrupt_coalesce intr_coal_tx;
> > struct virtnet_interrupt_coalesce intr_coal_rx;
> > @@ -2001,6 +2016,7 @@ static void skb_recv_done(struct virtqueue *rvq)
> > struct virtnet_info *vi = rvq->vdev->priv;
> > struct receive_queue *rq = &vi->rq[vq2rxq(rvq)];
> >
> > + rq->calls++;
> > virtqueue_napi_schedule(&rq->napi, rvq);
> > }
> >
> > @@ -2141,6 +2157,26 @@ static void virtnet_poll_cleantx(struct receive_queue *rq)
> > }
> > }
> >
> > +static void virtnet_rx_dim_work(struct work_struct *work);
> > +
> > +static void virtnet_rx_dim_update(struct virtnet_info *vi, struct receive_queue *rq)
> > +{
> > + struct dim_sample cur_sample = {};
> > +
> > + if (!rq->packets_in_napi)
> > + return;
> > +
> > + u64_stats_update_begin(&rq->stats.syncp);
> > + dim_update_sample(rq->calls,
> > + u64_stats_read(&rq->stats.packets),
> > + u64_stats_read(&rq->stats.bytes),
> > + &cur_sample);
> > + u64_stats_update_end(&rq->stats.syncp);
> > +
> > + net_dim(&rq->dim, cur_sample);
> > + rq->packets_in_napi = 0;
> > +}
> > +
> > static int virtnet_poll(struct napi_struct *napi, int budget)
> > {
> > struct receive_queue *rq =
> > @@ -2149,17 +2185,22 @@ static int virtnet_poll(struct napi_struct *napi, int budget)
> > struct send_queue *sq;
> > unsigned int received;
> > unsigned int xdp_xmit = 0;
> > + bool napi_complete;
> >
> > virtnet_poll_cleantx(rq);
> >
> > received = virtnet_receive(rq, budget, &xdp_xmit);
> > + rq->packets_in_napi += received;
> >
> > if (xdp_xmit & VIRTIO_XDP_REDIR)
> > xdp_do_flush();
> >
> > /* Out of packets? */
> > - if (received < budget)
> > - virtqueue_napi_complete(napi, rq->vq, received);
> > + if (received < budget) {
> > + napi_complete = virtqueue_napi_complete(napi, rq->vq, received);
> > + if (napi_complete && rq->dim_enabled)
> > + virtnet_rx_dim_update(vi, rq);
> > + }
> >
> > if (xdp_xmit & VIRTIO_XDP_TX) {
> > sq = virtnet_xdp_get_sq(vi);
> > @@ -2179,6 +2220,7 @@ static void virtnet_disable_queue_pair(struct virtnet_info *vi, int qp_index)
> > virtnet_napi_tx_disable(&vi->sq[qp_index].napi);
> > napi_disable(&vi->rq[qp_index].napi);
> > xdp_rxq_info_unreg(&vi->rq[qp_index].xdp_rxq);
> > + cancel_work_sync(&vi->rq[qp_index].dim.work);
> > }
> >
> > static int virtnet_enable_queue_pair(struct virtnet_info *vi, int qp_index)
> > @@ -2196,6 +2238,9 @@ static int virtnet_enable_queue_pair(struct virtnet_info *vi, int qp_index)
> > if (err < 0)
> > goto err_xdp_reg_mem_model;
> >
> > + INIT_WORK(&vi->rq[qp_index].dim.work, virtnet_rx_dim_work);
> > + vi->rq[qp_index].dim.mode = DIM_CQ_PERIOD_MODE_START_FROM_EQE;
>
> So in V2, you explained it can be done here but I want to know why it
> must be done here.
>
> For example, the refill_work is initialized in alloc_queues().
>
> > +
> > virtnet_napi_enable(vi->rq[qp_index].vq, &vi->rq[qp_index].napi);
> > virtnet_napi_tx_enable(vi, vi->sq[qp_index].vq, &vi->sq[qp_index].napi);
> >
> > @@ -2393,8 +2438,10 @@ static int virtnet_rx_resize(struct virtnet_info *vi,
> >
> > qindex = rq - vi->rq;
> >
> > - if (running)
> > + if (running) {
> > napi_disable(&rq->napi);
> > + cancel_work_sync(&rq->dim.work);
> > + }
> >
> > err = virtqueue_resize(rq->vq, ring_num, virtnet_rq_free_unused_buf);
> > if (err)
> > @@ -2403,8 +2450,10 @@ static int virtnet_rx_resize(struct virtnet_info *vi,
> > if (!try_fill_recv(vi, rq, GFP_KERNEL))
> > schedule_delayed_work(&vi->refill, 0);
> >
> > - if (running)
> > + if (running) {
> > + INIT_WORK(&rq->dim.work, virtnet_rx_dim_work);
> > virtnet_napi_enable(rq->vq, &rq->napi);
> > + }
> > return err;
> > }
> >
> > @@ -3341,24 +3390,55 @@ static int virtnet_send_tx_notf_coal_cmds(struct virtnet_info *vi,
> > static int virtnet_send_rx_notf_coal_cmds(struct virtnet_info *vi,
> > struct ethtool_coalesce *ec)
> > {
> > + bool rx_ctrl_dim_on = !!ec->use_adaptive_rx_coalesce;
> > + bool update = false, switch_dim;
> > struct scatterlist sgs_rx;
> > int i;
> >
> > - vi->ctrl->coal_rx.rx_usecs = cpu_to_le32(ec->rx_coalesce_usecs);
> > - vi->ctrl->coal_rx.rx_max_packets = cpu_to_le32(ec->rx_max_coalesced_frames);
> > - sg_init_one(&sgs_rx, &vi->ctrl->coal_rx, sizeof(vi->ctrl->coal_rx));
> > -
> > - if (!virtnet_send_command(vi, VIRTIO_NET_CTRL_NOTF_COAL,
> > - VIRTIO_NET_CTRL_NOTF_COAL_RX_SET,
> > - &sgs_rx))
> > - return -EINVAL;
> > + switch_dim = rx_ctrl_dim_on != vi->rx_dim_enabled;
> > + if (switch_dim) {
> > + if (rx_ctrl_dim_on) {
> > + if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_VQ_NOTF_COAL)) {
>
> So basically, I'm asking why we need to duplicate the check here?
>
> E.g caller has done the check for us:
>
> if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_NOTF_COAL))
> ret = virtnet_send_notf_coal_cmds(vi, ec);
> else
> ret = virtnet_coal_params_supported(ec);
Speak too fast, they have different features :(
But the point still, the logic needs some optimizations to reduce the
levels of nesting if/else.
Thanks
>
> ?
>
> Please also check other nested if/else, usually, too many levels of
> nesting is a hint that the logic needs to be optimized.
>
> Thanks
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