Re: [PATCH net-next] virtio_net: Add TX stop and wake counters

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Jan 30, 2024 at 08:25:21AM -0600, Daniel Jurgens wrote:
> Add a tx queue stop and wake counters, they are useful for debugging.
> 
> 	$ ethtool -S ens5f2 | grep 'tx_stop\|tx_wake'
> 	...
> 	tx_queue_1_tx_stop: 16726
> 	tx_queue_1_tx_wake: 16726
> 	...
> 	tx_queue_8_tx_stop: 1500110
> 	tx_queue_8_tx_wake: 1500110
> 
> Signed-off-by: Daniel Jurgens <danielj@nvidia.com>
> Reviewed-by: Parav Pandit <parav@nvidia.com>

Hmm isn't one always same as the other, except when queue is stopped?
And when it is stopped you can see that in the status?
So how is having two useful?


> ---
>  drivers/net/virtio_net.c | 26 ++++++++++++++++++++++++--
>  1 file changed, 24 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 3cb8aa193884..7e3c31ceaf7e 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -88,6 +88,8 @@ struct virtnet_sq_stats {
>  	u64_stats_t xdp_tx_drops;
>  	u64_stats_t kicks;
>  	u64_stats_t tx_timeouts;
> +	u64_stats_t tx_stop;
> +	u64_stats_t tx_wake;
>  };
>  
>  struct virtnet_rq_stats {
> @@ -112,6 +114,8 @@ static const struct virtnet_stat_desc virtnet_sq_stats_desc[] = {
>  	{ "xdp_tx_drops",	VIRTNET_SQ_STAT(xdp_tx_drops) },
>  	{ "kicks",		VIRTNET_SQ_STAT(kicks) },
>  	{ "tx_timeouts",	VIRTNET_SQ_STAT(tx_timeouts) },
> +	{ "tx_stop",		VIRTNET_SQ_STAT(tx_stop) },
> +	{ "tx_wake",		VIRTNET_SQ_STAT(tx_wake) },
>  };
>  
>  static const struct virtnet_stat_desc virtnet_rq_stats_desc[] = {
> @@ -843,6 +847,9 @@ static void check_sq_full_and_disable(struct virtnet_info *vi,
>  	 */
>  	if (sq->vq->num_free < 2+MAX_SKB_FRAGS) {
>  		netif_stop_subqueue(dev, qnum);
> +		u64_stats_update_begin(&sq->stats.syncp);
> +		u64_stats_inc(&sq->stats.tx_stop);
> +		u64_stats_update_end(&sq->stats.syncp);
>  		if (use_napi) {
>  			if (unlikely(!virtqueue_enable_cb_delayed(sq->vq)))
>  				virtqueue_napi_schedule(&sq->napi, sq->vq);
> @@ -851,6 +858,9 @@ static void check_sq_full_and_disable(struct virtnet_info *vi,
>  			free_old_xmit_skbs(sq, false);
>  			if (sq->vq->num_free >= 2+MAX_SKB_FRAGS) {
>  				netif_start_subqueue(dev, qnum);
> +				u64_stats_update_begin(&sq->stats.syncp);
> +				u64_stats_inc(&sq->stats.tx_wake);
> +				u64_stats_update_end(&sq->stats.syncp);
>  				virtqueue_disable_cb(sq->vq);
>  			}
>  		}
> @@ -2163,8 +2173,14 @@ static void virtnet_poll_cleantx(struct receive_queue *rq)
>  			free_old_xmit_skbs(sq, true);
>  		} while (unlikely(!virtqueue_enable_cb_delayed(sq->vq)));
>  
> -		if (sq->vq->num_free >= 2 + MAX_SKB_FRAGS)
> +		if (sq->vq->num_free >= 2 + MAX_SKB_FRAGS) {
> +			if (netif_tx_queue_stopped(txq)) {
> +				u64_stats_update_begin(&sq->stats.syncp);
> +				u64_stats_inc(&sq->stats.tx_wake);
> +				u64_stats_update_end(&sq->stats.syncp);
> +			}
>  			netif_tx_wake_queue(txq);
> +		}
>  
>  		__netif_tx_unlock(txq);
>  	}
> @@ -2310,8 +2326,14 @@ static int virtnet_poll_tx(struct napi_struct *napi, int budget)
>  	virtqueue_disable_cb(sq->vq);
>  	free_old_xmit_skbs(sq, true);
>  
> -	if (sq->vq->num_free >= 2 + MAX_SKB_FRAGS)
> +	if (sq->vq->num_free >= 2 + MAX_SKB_FRAGS) {
> +		if (netif_tx_queue_stopped(txq)) {
> +			u64_stats_update_begin(&sq->stats.syncp);
> +			u64_stats_inc(&sq->stats.tx_wake);
> +			u64_stats_update_end(&sq->stats.syncp);
> +		}
>  		netif_tx_wake_queue(txq);
> +	}
>  
>  	opaque = virtqueue_enable_cb_prepare(sq->vq);
>  
> -- 
> 2.42.0