On 17.10.2020 23:35, Vladimir Oltean wrote:
> DSA needs to push a header onto every packet on TX, and this might cause
> reallocation under certain scenarios, which might affect, for example,
> performance.
>
> But reallocated packets are not standardized in struct pcpu_sw_netstats,
> struct net_device_stats or anywhere else, it seems, so we need to roll
> our own extra netdevice statistics and expose them to ethtool.
>
> Signed-off-by: Vladimir Oltean <vladimir.olt...@nxp.com>
> ---
> net/dsa/dsa_priv.h | 9 +++++++++
> net/dsa/slave.c | 25 ++++++++++++++++++++++---
> 2 files changed, 31 insertions(+), 3 deletions(-)
>
> diff --git a/net/dsa/dsa_priv.h b/net/dsa/dsa_priv.h
> index 12998bf04e55..d39db7500cdd 100644
> --- a/net/dsa/dsa_priv.h
> +++ b/net/dsa/dsa_priv.h
> @@ -73,12 +73,21 @@ struct dsa_notifier_mtu_info {
> int mtu;
> };
>
> +/* Driver statistics, other than those in struct rtnl_link_stats64.
> + * These are collected per-CPU and aggregated by ethtool.
> + */
> +struct dsa_slave_stats {
> + __u64 tx_reallocs;
> + struct u64_stats_sync syncp;
> +} __aligned(1 * sizeof(u64));
> +
Wouldn't a simple unsigned long (like in struct net_device_stats) be
sufficient here? This would make handling the counter much simpler.
And as far as I understand we talk about a packet counter that is
touched in certain scenarios only.
> struct dsa_slave_priv {
> /* Copy of CPU port xmit for faster access in slave transmit hot path */
> struct sk_buff * (*xmit)(struct sk_buff *skb,
> struct net_device *dev);
>
> struct pcpu_sw_netstats __percpu *stats64;
> + struct dsa_slave_stats __percpu *extra_stats;
>
> struct gro_cells gcells;
>
> diff --git a/net/dsa/slave.c b/net/dsa/slave.c
> index 3bc5ca40c9fb..d4326940233c 100644
> --- a/net/dsa/slave.c
> +++ b/net/dsa/slave.c
> @@ -668,9 +668,10 @@ static void dsa_slave_get_strings(struct net_device *dev,
> strncpy(data + len, "tx_bytes", len);
> strncpy(data + 2 * len, "rx_packets", len);
> strncpy(data + 3 * len, "rx_bytes", len);
> + strncpy(data + 4 * len, "tx_reallocs", len);
> if (ds->ops->get_strings)
> ds->ops->get_strings(ds, dp->index, stringset,
> - data + 4 * len);
> + data + 5 * len);
> }
> }
>
> @@ -682,11 +683,13 @@ static void dsa_slave_get_ethtool_stats(struct
> net_device *dev,
> struct dsa_slave_priv *p = netdev_priv(dev);
> struct dsa_switch *ds = dp->ds;
> struct pcpu_sw_netstats *s;
> + struct dsa_slave_stats *e;
> unsigned int start;
> int i;
>
> for_each_possible_cpu(i) {
> u64 tx_packets, tx_bytes, rx_packets, rx_bytes;
> + u64 tx_reallocs;
>
> s = per_cpu_ptr(p->stats64, i);
> do {
> @@ -696,13 +699,21 @@ static void dsa_slave_get_ethtool_stats(struct
> net_device *dev,
> rx_packets = s->rx_packets;
> rx_bytes = s->rx_bytes;
> } while (u64_stats_fetch_retry_irq(&s->syncp, start));
> +
> + e = per_cpu_ptr(p->extra_stats, i);
> + do {
> + start = u64_stats_fetch_begin_irq(&e->syncp);
> + tx_reallocs = e->tx_reallocs;
> + } while (u64_stats_fetch_retry_irq(&e->syncp, start));
> +
> data[0] += tx_packets;
> data[1] += tx_bytes;
> data[2] += rx_packets;
> data[3] += rx_bytes;
> + data[4] += tx_reallocs;
> }
> if (ds->ops->get_ethtool_stats)
> - ds->ops->get_ethtool_stats(ds, dp->index, data + 4);
> + ds->ops->get_ethtool_stats(ds, dp->index, data + 5);
> }
>
> static int dsa_slave_get_sset_count(struct net_device *dev, int sset)
> @@ -713,7 +724,7 @@ static int dsa_slave_get_sset_count(struct net_device
> *dev, int sset)
> if (sset == ETH_SS_STATS) {
> int count;
>
> - count = 4;
> + count = 5;
> if (ds->ops->get_sset_count)
> count += ds->ops->get_sset_count(ds, dp->index, sset);
>
> @@ -1806,6 +1817,12 @@ int dsa_slave_create(struct dsa_port *port)
> free_netdev(slave_dev);
> return -ENOMEM;
> }
> + p->extra_stats = netdev_alloc_pcpu_stats(struct dsa_slave_stats);
> + if (!p->extra_stats) {
> + free_percpu(p->stats64);
> + free_netdev(slave_dev);
> + return -ENOMEM;
> + }
>
> ret = gro_cells_init(&p->gcells, slave_dev);
> if (ret)
> @@ -1864,6 +1881,7 @@ int dsa_slave_create(struct dsa_port *port)
> out_gcells:
> gro_cells_destroy(&p->gcells);
> out_free:
> + free_percpu(p->extra_stats);
> free_percpu(p->stats64);
> free_netdev(slave_dev);
> port->slave = NULL;
> @@ -1886,6 +1904,7 @@ void dsa_slave_destroy(struct net_device *slave_dev)
> dsa_slave_notify(slave_dev, DSA_PORT_UNREGISTER);
> phylink_destroy(dp->pl);
> gro_cells_destroy(&p->gcells);
> + free_percpu(p->extra_stats);
> free_percpu(p->stats64);
> free_netdev(slave_dev);
> }
>
