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Date: Tue, 18 Jun 2024 09:52:15 +0200
From: Jiri Pirko <jiri@...nulli.us>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: netdev@...r.kernel.org, davem@...emloft.net, edumazet@...gle.com,
kuba@...nel.org, pabeni@...hat.com, jasowang@...hat.com,
xuanzhuo@...ux.alibaba.com, virtualization@...ts.linux.dev,
ast@...nel.org, daniel@...earbox.net, hawk@...nel.org,
john.fastabend@...il.com, dave.taht@...il.com,
kerneljasonxing@...il.com, hengqi@...ux.alibaba.com
Subject: Re: [PATCH net-next v2] virtio_net: add support for Byte Queue Limits
Mon, Jun 17, 2024 at 06:14:11PM CEST, mst@...hat.com wrote:
>On Wed, Jun 12, 2024 at 07:08:51PM +0200, Jiri Pirko wrote:
>> From: Jiri Pirko <jiri@...dia.com>
>>
>> Add support for Byte Queue Limits (BQL).
>>
>> Tested on qemu emulated virtio_net device with 1, 2 and 4 queues.
>> Tested with fq_codel and pfifo_fast. Super netperf with 50 threads is
>> running in background. Netperf TCP_RR results:
>>
>> NOBQL FQC 1q: 159.56 159.33 158.50 154.31 agv: 157.925
>> NOBQL FQC 2q: 184.64 184.96 174.73 174.15 agv: 179.62
>> NOBQL FQC 4q: 994.46 441.96 416.50 499.56 agv: 588.12
>> NOBQL PFF 1q: 148.68 148.92 145.95 149.48 agv: 148.2575
>> NOBQL PFF 2q: 171.86 171.20 170.42 169.42 agv: 170.725
>> NOBQL PFF 4q: 1505.23 1137.23 2488.70 3507.99 agv: 2159.7875
>> BQL FQC 1q: 1332.80 1297.97 1351.41 1147.57 agv: 1282.4375
>> BQL FQC 2q: 768.30 817.72 864.43 974.40 agv: 856.2125
>> BQL FQC 4q: 945.66 942.68 878.51 822.82 agv: 897.4175
>> BQL PFF 1q: 149.69 151.49 149.40 147.47 agv: 149.5125
>> BQL PFF 2q: 2059.32 798.74 1844.12 381.80 agv: 1270.995
>> BQL PFF 4q: 1871.98 4420.02 4916.59 13268.16 agv: 6119.1875
>>
>> Signed-off-by: Jiri Pirko <jiri@...dia.com>
>> ---
>> v1->v2:
>> - moved netdev_tx_completed_queue() call into __free_old_xmit(),
>> propagate use_napi flag to __free_old_xmit() and only call
>> netdev_tx_completed_queue() in case it is true
>> - added forgotten call to netdev_tx_reset_queue()
>> - fixed stats for xdp packets
>> - fixed bql accounting when __free_old_xmit() is called from xdp path
>> - handle the !use_napi case in start_xmit() kick section
>> ---
>> drivers/net/virtio_net.c | 50 +++++++++++++++++++++++++---------------
>> 1 file changed, 32 insertions(+), 18 deletions(-)
>>
>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>> index 61a57d134544..5863c663ccab 100644
>> --- a/drivers/net/virtio_net.c
>> +++ b/drivers/net/virtio_net.c
>> @@ -84,7 +84,9 @@ struct virtnet_stat_desc {
>>
>> struct virtnet_sq_free_stats {
>> u64 packets;
>> + u64 xdp_packets;
>> u64 bytes;
>> + u64 xdp_bytes;
>> };
>>
>> struct virtnet_sq_stats {
>> @@ -506,29 +508,33 @@ static struct xdp_frame *ptr_to_xdp(void *ptr)
>> return (struct xdp_frame *)((unsigned long)ptr & ~VIRTIO_XDP_FLAG);
>> }
>>
>> -static void __free_old_xmit(struct send_queue *sq, bool in_napi,
>> +static void __free_old_xmit(struct send_queue *sq, struct netdev_queue *txq,
>> + bool in_napi, bool use_napi,
>> struct virtnet_sq_free_stats *stats)
>> {
>> unsigned int len;
>> void *ptr;
>>
>> while ((ptr = virtqueue_get_buf(sq->vq, &len)) != NULL) {
>> - ++stats->packets;
>> -
>> if (!is_xdp_frame(ptr)) {
>> struct sk_buff *skb = ptr;
>>
>> pr_debug("Sent skb %p\n", skb);
>>
>> + stats->packets++;
>> stats->bytes += skb->len;
>> napi_consume_skb(skb, in_napi);
>> } else {
>> struct xdp_frame *frame = ptr_to_xdp(ptr);
>>
>> - stats->bytes += xdp_get_frame_len(frame);
>> + stats->xdp_packets++;
>> + stats->xdp_bytes += xdp_get_frame_len(frame);
>> xdp_return_frame(frame);
>> }
>> }
>> + if (use_napi)
>> + netdev_tx_completed_queue(txq, stats->packets, stats->bytes);
>> +
>> }
>>
>> /* Converting between virtqueue no. and kernel tx/rx queue no.
>> @@ -955,21 +961,22 @@ static void virtnet_rq_unmap_free_buf(struct virtqueue *vq, void *buf)
>> virtnet_rq_free_buf(vi, rq, buf);
>> }
>>
>> -static void free_old_xmit(struct send_queue *sq, bool in_napi)
>> +static void free_old_xmit(struct send_queue *sq, struct netdev_queue *txq,
>> + bool in_napi, bool use_napi)
>> {
>> struct virtnet_sq_free_stats stats = {0};
>>
>> - __free_old_xmit(sq, in_napi, &stats);
>> + __free_old_xmit(sq, txq, in_napi, use_napi, &stats);
>>
>> /* Avoid overhead when no packets have been processed
>> * happens when called speculatively from start_xmit.
>> */
>> - if (!stats.packets)
>> + if (!stats.packets && !stats.xdp_packets)
>> return;
>>
>> u64_stats_update_begin(&sq->stats.syncp);
>> - u64_stats_add(&sq->stats.bytes, stats.bytes);
>> - u64_stats_add(&sq->stats.packets, stats.packets);
>> + u64_stats_add(&sq->stats.bytes, stats.bytes + stats.xdp_bytes);
>> + u64_stats_add(&sq->stats.packets, stats.packets + stats.xdp_packets);
>> u64_stats_update_end(&sq->stats.syncp);
>> }
>>
>> @@ -1003,7 +1010,9 @@ static void check_sq_full_and_disable(struct virtnet_info *vi,
>> * early means 16 slots are typically wasted.
>> */
>> if (sq->vq->num_free < 2+MAX_SKB_FRAGS) {
>> - netif_stop_subqueue(dev, qnum);
>> + struct netdev_queue *txq = netdev_get_tx_queue(dev, qnum);
>> +
>> + netif_tx_stop_queue(txq);
>> u64_stats_update_begin(&sq->stats.syncp);
>> u64_stats_inc(&sq->stats.stop);
>> u64_stats_update_end(&sq->stats.syncp);
>> @@ -1012,7 +1021,7 @@ static void check_sq_full_and_disable(struct virtnet_info *vi,
>> virtqueue_napi_schedule(&sq->napi, sq->vq);
>> } else if (unlikely(!virtqueue_enable_cb_delayed(sq->vq))) {
>> /* More just got used, free them then recheck. */
>> - free_old_xmit(sq, false);
>> + free_old_xmit(sq, txq, false, use_napi);
>> if (sq->vq->num_free >= 2+MAX_SKB_FRAGS) {
>> netif_start_subqueue(dev, qnum);
>> u64_stats_update_begin(&sq->stats.syncp);
>> @@ -1138,7 +1147,8 @@ static int virtnet_xdp_xmit(struct net_device *dev,
>> }
>>
>> /* Free up any pending old buffers before queueing new ones. */
>> - __free_old_xmit(sq, false, &stats);
>> + __free_old_xmit(sq, netdev_get_tx_queue(dev, sq - vi->sq),
>> + false, sq->napi.weight, &stats);
>
>
>So what happens if sq->napi.weight changes while packet is in the queue?
>What prevents that?
Sigh. You are correct. That is what Jason points out as well.
>
>
>
>>
>> for (i = 0; i < n; i++) {
>> struct xdp_frame *xdpf = frames[i];
>> @@ -2313,7 +2323,7 @@ static void virtnet_poll_cleantx(struct receive_queue *rq)
>>
>> do {
>> virtqueue_disable_cb(sq->vq);
>> - free_old_xmit(sq, true);
>> + free_old_xmit(sq, txq, true, true);
>> } while (unlikely(!virtqueue_enable_cb_delayed(sq->vq)));
>>
>> if (sq->vq->num_free >= 2 + MAX_SKB_FRAGS) {
>> @@ -2412,6 +2422,7 @@ static int virtnet_enable_queue_pair(struct virtnet_info *vi, int qp_index)
>> goto err_xdp_reg_mem_model;
>>
>> virtnet_napi_enable(vi->rq[qp_index].vq, &vi->rq[qp_index].napi);
>> + netdev_tx_reset_queue(netdev_get_tx_queue(vi->dev, qp_index));
>> virtnet_napi_tx_enable(vi, vi->sq[qp_index].vq, &vi->sq[qp_index].napi);
>>
>> return 0;
>> @@ -2471,7 +2482,7 @@ static int virtnet_poll_tx(struct napi_struct *napi, int budget)
>> txq = netdev_get_tx_queue(vi->dev, index);
>> __netif_tx_lock(txq, raw_smp_processor_id());
>> virtqueue_disable_cb(sq->vq);
>> - free_old_xmit(sq, true);
>> + free_old_xmit(sq, txq, true, true);
>>
>> if (sq->vq->num_free >= 2 + MAX_SKB_FRAGS) {
>> if (netif_tx_queue_stopped(txq)) {
>> @@ -2559,17 +2570,18 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
>> struct send_queue *sq = &vi->sq[qnum];
>> int err;
>> struct netdev_queue *txq = netdev_get_tx_queue(dev, qnum);
>> - bool kick = !netdev_xmit_more();
>> + bool xmit_more = netdev_xmit_more();
>> bool use_napi = sq->napi.weight;
>> + bool kick;
>>
>> /* Free up any pending old buffers before queueing new ones. */
>> do {
>> if (use_napi)
>> virtqueue_disable_cb(sq->vq);
>>
>> - free_old_xmit(sq, false);
>> + free_old_xmit(sq, txq, false, use_napi);
>>
>> - } while (use_napi && kick &&
>> + } while (use_napi && !xmit_more &&
>> unlikely(!virtqueue_enable_cb_delayed(sq->vq)));
>>
>> /* timestamp packet in software */
>> @@ -2598,7 +2610,9 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
>>
>> check_sq_full_and_disable(vi, dev, sq);
>>
>> - if (kick || netif_xmit_stopped(txq)) {
>> + kick = use_napi ? __netdev_tx_sent_queue(txq, skb->len, xmit_more) :
>> + !xmit_more && netif_xmit_stopped(txq);
>> + if (kick) {
>> if (virtqueue_kick_prepare(sq->vq) && virtqueue_notify(sq->vq)) {
>> u64_stats_update_begin(&sq->stats.syncp);
>> u64_stats_inc(&sq->stats.kicks);
>> --
>> 2.45.1
>
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