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

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

On Tue, Jan 30, 2024 at 03:43:48PM +0000, Daniel Jurgens wrote:
> > From: Heng Qi <hengqi@linux.alibaba.com>
> > Sent: Tuesday, January 30, 2024 9:17 AM
> > 在 2024/1/30 下午10:25, Daniel Jurgens 写道:
> > > 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>
> > > ---
> > >   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;
> > >   };
> > 
> > Hi Daniel!
> > 
> > tx_stop/wake only counts the status in the I/O path.
> > Do the status of virtnet_config_changed_work and virtnet_tx_resize need to
> > be counted?
> > 
> 
> My motivation for the counter is detecting full TX queues. I don't think counting them in the control path is useful, but it can be done if you disagree.

Do we then just want "tx full" counter?

> > Thanks,
> > Heng
> > 
> > >
> > >   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);
> > >
>