Date: Wed, 15 May 2024 02:19:33 -0500
From: Joe Damato <jdamato@...tly.com>
To: Tariq Toukan <ttoukan.linux@...il.com>
Cc: linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	zyjzyj2000@...il.com, nalramli@...tly.com,
	Saeed Mahameed <saeedm@...dia.com>,
	Leon Romanovsky <leon@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Richard Cochran <richardcochran@...il.com>,
	"open list:MELLANOX MLX5 core VPI driver" <linux-rdma@...r.kernel.org>,
	Tariq Toukan <tariqt@...dia.com>
Subject: Re: [PATCH net-next v2 1/1] net/mlx5e: Add per queue netdev-genl
 stats

On Tue, May 14, 2024 at 09:44:37PM +0300, Tariq Toukan wrote:
> 
> 
> On 10/05/2024 7:17, Joe Damato wrote:
> > Add functions to support the netdev-genl per queue stats API.
> > 
> > ./cli.py --spec netlink/specs/netdev.yaml \
> > --dump qstats-get --json '{"scope": "queue"}'
> > 
> > ...snip
> > 
> >   {'ifindex': 7,
> >    'queue-id': 62,
> >    'queue-type': 'rx',
> >    'rx-alloc-fail': 0,
> >    'rx-bytes': 105965251,
> >    'rx-packets': 179790},
> >   {'ifindex': 7,
> >    'queue-id': 0,
> >    'queue-type': 'tx',
> >    'tx-bytes': 9402665,
> >    'tx-packets': 17551},
> > 
> > ...snip
> > 
> > Also tested with the script tools/testing/selftests/drivers/net/stats.py
> > in several scenarios to ensure stats tallying was correct:
> > 
> > - on boot (default queue counts)
> > - adjusting queue count up or down (ethtool -L eth0 combined ...)
> > - adding mqprio TCs
> > 
> > Signed-off-by: Joe Damato <jdamato@...tly.com>
> > ---
> >   .../net/ethernet/mellanox/mlx5/core/en_main.c | 144 ++++++++++++++++++
> >   1 file changed, 144 insertions(+)
> > 
> > diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> > index ffe8919494d5..4a675d8b31b5 100644
> > --- a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> > +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> > @@ -39,6 +39,7 @@
> >   #include <linux/debugfs.h>
> >   #include <linux/if_bridge.h>
> >   #include <linux/filter.h>
> > +#include <net/netdev_queues.h>
> >   #include <net/page_pool/types.h>
> >   #include <net/pkt_sched.h>
> >   #include <net/xdp_sock_drv.h>
> > @@ -5282,6 +5283,148 @@ static bool mlx5e_tunnel_any_tx_proto_supported(struct mlx5_core_dev *mdev)
> >   	return (mlx5_vxlan_allowed(mdev->vxlan) || mlx5_geneve_tx_allowed(mdev));
> >   }
> > +static void mlx5e_get_queue_stats_rx(struct net_device *dev, int i,
> > +				     struct netdev_queue_stats_rx *stats)
> > +{
> > +	struct mlx5e_priv *priv = netdev_priv(dev);
> > +
> > +	if (mlx5e_is_uplink_rep(priv))
> > +		return;
> > +
> > +	struct mlx5e_channel_stats *channel_stats = priv->channel_stats[i];
> > +	struct mlx5e_rq_stats *xskrq_stats = &channel_stats->xskrq;
> > +	struct mlx5e_rq_stats *rq_stats = &channel_stats->rq;
> > +
> 
> Don't we allow variable declaration only at the beginning of a block?
> Is this style accepted in the networking subsystem?
> 
> > +	stats->packets = rq_stats->packets + xskrq_stats->packets;
> > +	stats->bytes = rq_stats->bytes + xskrq_stats->bytes;
> > +	stats->alloc_fail = rq_stats->buff_alloc_err +
> > +			    xskrq_stats->buff_alloc_err;
> > +}
> > +
> > +static void mlx5e_get_queue_stats_tx(struct net_device *dev, int i,
> > +				     struct netdev_queue_stats_tx *stats)
> > +{
> > +	struct mlx5e_priv *priv = netdev_priv(dev);
> > +	struct net_device *netdev = priv->netdev;
> > +	struct mlx5e_txqsq *sq;
> > +	int j;
> > +
> > +	if (mlx5e_is_uplink_rep(priv))
> > +		return;
> > +
> > +	for (j = 0; j < netdev->num_tx_queues; j++) {
> > +		sq = priv->txq2sq[j];
> 
> No sq instance in case interface is down.

This seems easily fixable by checking:

  priv->channels.num > 0

> This should be a simple arithmetic calculation.

I'm not sure why I can't use txq2sq? Please see below for my
explanation about why I think txq2sq might be all I need.

> Need to expose the proper functions for this calculation, and use it here
> and in the sq create flows.

I re-read the code several times and my apologies, but I am probably
still missing something.

I don't think a calculation function is necessary (see below), but
if one is really needed, I'd probably add something like:

  static inline int tc_to_txq_ix(struct mlx5e_channel *c,
                                 struct mlx5e_params *params,
                                 int tc)
  {
         return c->ix + tc * params->num_channels;
  }

And call it from mlx5e_open_sqs.

But, I don't understand why any calculation is needed in
mlx5e_get_queue_stats_tx. Please see below for explanation.

> 
> Here it seems that you need a very involved user, so he passes the correct
> index i of the SQ that he's interested in..
> 
> > +		if (sq->ch_ix == i) {
> 
> So you're looking for the first SQ on channel i?
> But there might be multiple SQs on channel i...
> Also, this SQ might be already included in the base stats.
> In addition, this i might be too large for a channel index (num_tx_queues
> can be 8 * num_channels)
>
> The logic here (of mapping from i in num_tx_queues to SQ stats) needs
> careful definition.

I read your comments a few times and read the mlx5 source and I am
probably still missing something obvious here; my apologies.

In net/core/netdev-genl.c, calls to the driver's get_queue_stats_tx
appear to pass [0, netdev->real_num_tx_queues) as i.

I think this means i is a txq_ix in mlx5, because mlx5 sets
netdev->real_num_tx_queues in mlx5e_update_tx_netdev_queues, as:

  nch * ntc + qos_queues

which when expanded is

  priv->channels.params.num_channels * mlx5e_get_dcb_num_tc + qos_queues

So, net/core/netdev-genl.c will be using 0 up to that expression as
i when calling mlx5e_get_queue_stats_tx.

In mlx5: 
  - mlx5e_activate_priv_channels calls mlx5e_build_txq_maps which
    generates priv->txq2sq[txq_ix] = sq for every mlx5e_get_dcb_num_tc
    of every priv->channels.num.
 
This seems to happen every time mlx5e_activate_priv_channels is
called, which I think means that priv->txq2sq is always up to date
and will give the right sq for a given txq_ix (assuming the device
isn't down).

Putting all of this together, I think that mlx5e_get_queue_stats_tx
might need to be something like:

  mutex_lock(&priv->state_lock);
  if (priv->channels.num > 0) {
          sq = priv->txq2sq[i];
          stats->packets = sq->stats->packets;
          stats->bytes = sq->stats->bytes;
  }
  mutex_unlock(&priv->state_lock);

Is this still incorrect somehow?

If so, could you explain a bit more about why a calculation is
needed? It seems like txq2sq would provide the mapping from txq_ix's
(which is what mlx5e_get_queue_stats_tx gets as 'i') and an sq,
which seems like all I would need?

Sorry if I am still not following here.

> > +			stats->packets = sq->stats->packets;
> > +			stats->bytes = sq->stats->bytes;
> > +			return;
> > +		}
> > +	}
> > +}
> > +
> > +static void mlx5e_get_base_stats(struct net_device *dev,
> > +				 struct netdev_queue_stats_rx *rx,
> > +				 struct netdev_queue_stats_tx *tx)
> > +{
> > +	struct mlx5e_priv *priv = netdev_priv(dev);
> > +	int i, j;
> > +
> > +	if (!mlx5e_is_uplink_rep(priv)) {
> > +		rx->packets = 0;
> > +		rx->bytes = 0;
> > +		rx->alloc_fail = 0;
> > +
> > +		/* compute stats for deactivated RX queues
> > +		 *
> > +		 * if priv->channels.num == 0 the device is down, so compute
> > +		 * stats for every queue.
> > +		 *
> > +		 * otherwise, compute only the queues which have been deactivated.
> > +		 */
> > +		if (priv->channels.num == 0)
> > +			i = 0;
> > +		else
> > +			i = priv->channels.params.num_channels;
> > +
> > +		for (; i < priv->stats_nch; i++) {
> > +			struct mlx5e_channel_stats *channel_stats = priv->channel_stats[i];
> > +			struct mlx5e_rq_stats *xskrq_stats = &channel_stats->xskrq;
> > +			struct mlx5e_rq_stats *rq_stats = &channel_stats->rq;
> > +
> > +			rx->packets += rq_stats->packets + xskrq_stats->packets;
> > +			rx->bytes += rq_stats->bytes + xskrq_stats->bytes;
> > +			rx->alloc_fail += rq_stats->buff_alloc_err +
> > +					  xskrq_stats->buff_alloc_err;
> 
> Isn't this equivalent to mlx5e_get_queue_stats_rx(i) ?
> 
> > +		}
> > +
> > +		if (priv->rx_ptp_opened) {
> > +			struct mlx5e_rq_stats *rq_stats = &priv->ptp_stats.rq;
> > +
> > +			rx->packets += rq_stats->packets;
> > +			rx->bytes += rq_stats->bytes;
> > +		}
> > +	}
> > +
> > +	tx->packets = 0;
> > +	tx->bytes = 0;
> > +
> > +	/* three TX cases to handle:
> > +	 *
> > +	 * case 1: priv->channels.num == 0, get the stats for every TC
> > +	 *         on every queue.
> > +	 *
> > +	 * case 2: priv->channel.num > 0, so get the stats for every TC on
> > +	 *         every deactivated queue.
> > +	 *
> > +	 * case 3: the number of TCs has changed, so get the stats for the
> > +	 *         inactive TCs on active TX queues (handled in the second loop
> > +	 *         below).
> > +	 */
> > +	if (priv->channels.num == 0)
> > +		i = 0;
> > +	else
> > +		i = priv->channels.params.num_channels;
> > +
> 
> All reads/writes to priv->channels must be under the priv->state_lock.
> 
> > +	for (; i < priv->stats_nch; i++) {
> > +		struct mlx5e_channel_stats *channel_stats = priv->channel_stats[i];
> > +
> > +		for (j = 0; j < priv->max_opened_tc; j++) {
> > +			struct mlx5e_sq_stats *sq_stats = &channel_stats->sq[j];
> > +
> > +			tx->packets += sq_stats->packets;
> > +			tx->bytes += sq_stats->bytes;
> > +		}
> > +	}
> > +
> > +	/* Handle case 3 described above. */
> > +	for (i = 0; i < priv->channels.params.num_channels; i++) {
> > +		struct mlx5e_channel_stats *channel_stats = priv->channel_stats[i];
> > +		u8 dcb_num_tc = mlx5e_get_dcb_num_tc(&priv->channels.params);
> > +
> > +		for (j = dcb_num_tc; j < priv->max_opened_tc; j++) {
> > +			struct mlx5e_sq_stats *sq_stats = &channel_stats->sq[j];
> > +
> > +			tx->packets += sq_stats->packets;
> > +			tx->bytes += sq_stats->bytes;
> > +		}
> > +	}
> > +
> > +	if (priv->tx_ptp_opened) {
> > +		for (j = 0; j < priv->max_opened_tc; j++) {
> > +			struct mlx5e_sq_stats *sq_stats = &priv->ptp_stats.sq[j];
> > +
> > +			tx->packets    += sq_stats->packets;
> > +			tx->bytes      += sq_stats->bytes;
> > +		}
> > +	}
> > +}
> > +
> > +static const struct netdev_stat_ops mlx5e_stat_ops = {
> > +	.get_queue_stats_rx     = mlx5e_get_queue_stats_rx,
> > +	.get_queue_stats_tx     = mlx5e_get_queue_stats_tx,
> > +	.get_base_stats         = mlx5e_get_base_stats,
> > +};
> > +
> >   static void mlx5e_build_nic_netdev(struct net_device *netdev)
> >   {
> >   	struct mlx5e_priv *priv = netdev_priv(netdev);
> > @@ -5299,6 +5442,7 @@ static void mlx5e_build_nic_netdev(struct net_device *netdev)
> >   	netdev->watchdog_timeo    = 15 * HZ;
> > +	netdev->stat_ops          = &mlx5e_stat_ops;
> >   	netdev->ethtool_ops	  = &mlx5e_ethtool_ops;
> >   	netdev->vlan_features    |= NETIF_F_SG;

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