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

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Message-ID:
 <CH0PR12MB858067B9DB6BCEE10519F957C97D2@CH0PR12MB8580.namprd12.prod.outlook.com>
Date: Tue, 30 Jan 2024 17:33:57 +0000
From: Daniel Jurgens <danielj@...dia.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
CC: "netdev@...r.kernel.org" <netdev@...r.kernel.org>, "jasowang@...hat.com"
	<jasowang@...hat.com>, "xuanzhuo@...ux.alibaba.com"
	<xuanzhuo@...ux.alibaba.com>, "virtualization@...ts.linux.dev"
	<virtualization@...ts.linux.dev>, "davem@...emloft.net"
	<davem@...emloft.net>, "edumazet@...gle.com" <edumazet@...gle.com>,
	"kuba@...nel.org" <kuba@...nel.org>, "abeni@...hat.com" <abeni@...hat.com>,
	Parav Pandit <parav@...dia.com>
Subject: RE: [PATCH net-next] virtio_net: Add TX stop and wake counters

> From: Michael S. Tsirkin <mst@...hat.com>
> Sent: Tuesday, January 30, 2024 9:53 AM
> On Tue, Jan 30, 2024 at 03:50:29PM +0000, Daniel Jurgens wrote:
> > > From: Michael S. Tsirkin <mst@...hat.com>
> > > Sent: Tuesday, January 30, 2024 9:42 AM On Tue, Jan 30, 2024 at
> > > 03:40:21PM +0000, Daniel Jurgens wrote:
> > > > > From: Michael S. Tsirkin <mst@...hat.com>
> > > > > Sent: Tuesday, January 30, 2024 8:58 AM
> > > > >
> > > > > 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@...dia.com>
> > > > > > Reviewed-by: Parav Pandit <parav@...dia.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?
> > > >
> > > > At idle the counters will be the same, unless a tx_timeout occurs.
> > > > But
> > > under load they can be monitored to see which queues are stopped and
> > > get an idea of how long they are stopped.
> > >
> > > how does it give you the idea of how long they are stopped?
> >
> > By serially monitoring the counter you can see stops that persist long
> intervals that are less than the tx_timeout time.
> 
> Why don't you monitor queue status directly?

How? I don't know of any interface to check if a queue is stopped.

> 
> > >
> > > > Other net drivers (not all), also have the wake counter.
> > >
> > > Examples?
> >
> > [danielj@...mtx-051 upstream]$ ethtool -i ens2f1np1
> > driver: mlx5_core
> > version: 6.7.0+
> > ...
> > [danielj@...mtx-051 upstream]$ ethtool -S ens2f1np1 | grep wake
> >      tx_queue_wake: 0
> >      tx0_wake: 0
> 
> Do they have a stop counter too?

Yes:
[danielj@...mtx-051 upstream]$ ethtool -S ens2f1np1 | grep 'stop\|wake'
     tx_queue_stopped: 0
     tx_queue_wake: 0
     tx0_stopped: 0
     tx0_wake: 0
     ....

> 
> > >
> > > > In my opinion it makes the stop counter more useful, at little cost.
> > > >
> > > > >
> > > > >
> > > > > > ---
> > > > > >  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