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Message-ID: <Zj34VgY5yT7259iT@nanopsycho.orion>
Date: Fri, 10 May 2024 12:35:02 +0200
From: Jiri Pirko <jiri@...nulli.us>
To: Heng Qi <hengqi@...ux.alibaba.com>
Cc: davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
	pabeni@...hat.com, mst@...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, netdev@...r.kernel.org
Subject: Re: [patch net-next] virtio_net: add support for Byte Queue Limits

Fri, May 10, 2024 at 09:11:16AM CEST, hengqi@...ux.alibaba.com wrote:
>On Thu,  9 May 2024 13:46:15 +0200, Jiri Pirko <jiri@...nulli.us> wrote:
>> From: Jiri Pirko <jiri@...dia.com>
>> 
>> Add support for Byte Queue Limits (BQL).
>
>Historically both Jason and Michael have attempted to support BQL
>for virtio-net, for example:
>
>https://lore.kernel.org/netdev/21384cb5-99a6-7431-1039-b356521e1bc3@redhat.com/
>
>These discussions focus primarily on:
>
>1. BQL is based on napi tx. Therefore, the transfer of statistical information
>needs to rely on the judgment of use_napi. When the napi mode is switched to
>orphan, some statistical information will be lost, resulting in temporary
>inaccuracy in BQL.
>
>2. If tx dim is supported, orphan mode may be removed and tx irq will be more
>reasonable. This provides good support for BQL.

Thanks for the pointers, will check that out.


>
>Thanks.
>
>> 
>> Signed-off-by: Jiri Pirko <jiri@...dia.com>
>> ---
>>  drivers/net/virtio_net.c | 33 ++++++++++++++++++++-------------
>>  1 file changed, 20 insertions(+), 13 deletions(-)
>> 
>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>> index 218a446c4c27..c53d6dc6d332 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 {
>> @@ -512,19 +514,19 @@ static void __free_old_xmit(struct send_queue *sq, bool in_napi,
>>  	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);
>>  		}
>>  	}
>> @@ -965,7 +967,8 @@ 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)
>>  {
>>  	struct virtnet_sq_free_stats stats = {0};
>>  
>> @@ -974,9 +977,11 @@ static void free_old_xmit(struct send_queue *sq, bool in_napi)
>>  	/* 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;
>>  
>> +	netdev_tx_completed_queue(txq, stats.packets, stats.bytes);
>> +
>>  	u64_stats_update_begin(&sq->stats.syncp);
>>  	u64_stats_add(&sq->stats.bytes, stats.bytes);
>>  	u64_stats_add(&sq->stats.packets, stats.packets);
>> @@ -1013,13 +1018,15 @@ 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);
>>  		if (use_napi) {
>>  			if (unlikely(!virtqueue_enable_cb_delayed(sq->vq)))
>>  				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);
>>  			if (sq->vq->num_free >= 2+MAX_SKB_FRAGS) {
>>  				netif_start_subqueue(dev, qnum);
>>  				virtqueue_disable_cb(sq->vq);
>> @@ -2319,7 +2326,7 @@ 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);
>>  		} while (unlikely(!virtqueue_enable_cb_delayed(sq->vq)));
>>  
>>  		if (sq->vq->num_free >= 2 + MAX_SKB_FRAGS)
>> @@ -2471,7 +2478,7 @@ 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);
>>  
>>  	if (sq->vq->num_free >= 2 + MAX_SKB_FRAGS)
>>  		netif_tx_wake_queue(txq);
>> @@ -2553,7 +2560,7 @@ 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;
>>  
>>  	/* Free up any pending old buffers before queueing new ones. */
>> @@ -2561,9 +2568,9 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
>>  		if (use_napi)
>>  			virtqueue_disable_cb(sq->vq);
>>  
>> -		free_old_xmit(sq, false);
>> +		free_old_xmit(sq, txq, false);
>>  
>> -	} while (use_napi && kick &&
>> +	} while (use_napi && !xmit_more &&
>>  	       unlikely(!virtqueue_enable_cb_delayed(sq->vq)));
>>  
>>  	/* timestamp packet in software */
>> @@ -2592,7 +2599,7 @@ 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)) {
>> +	if (__netdev_tx_sent_queue(txq, skb->len, xmit_more)) {
>>  		if (virtqueue_kick_prepare(sq->vq) && virtqueue_notify(sq->vq)) {
>>  			u64_stats_update_begin(&sq->stats.syncp);
>>  			u64_stats_inc(&sq->stats.kicks);
>> -- 
>> 2.44.0
>> 
>> 

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