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Date: Tue, 24 Mar 2020 23:21:39 +0900
From: Toshiaki Makita <toshiaki.makita1@...il.com>
To: Lorenzo Bianconi <lorenzo@...nel.org>
Cc: netdev@...r.kernel.org, davem@...emloft.net, brouer@...hat.com,
dsahern@...il.com, lorenzo.bianconi@...hat.com, toke@...hat.com
Subject: Re: [PATCH net-next 4/5] veth: introduce more xdp counters
On 2020/03/24 2:31, Lorenzo Bianconi wrote:
>> On 2020/03/21 23:30, Lorenzo Bianconi wrote:
>>>> On 2020/03/20 22:37, Lorenzo Bianconi wrote:
>>>>>> On 2020/03/20 1:41, Lorenzo Bianconi wrote:
>
> [...]
>
>> As veth_xdp_xmit really does not use tx queue but select peer rxq directly,
>> per_cpu sounds more appropriate than per-queue.
>> One concern is consistency. Per-queue rx stats and per-cpu tx stats (or only
>> sum of them?) looks inconsistent.
>> One alternative way is to change the queue selection login in veth_xdp_xmit
>> and select txq instead of rxq. Then select peer rxq from txq, like
>> veth_xmit. Accounting per queue tx stats is possible only when we can
>> determine which txq is used.
>>
>> Something like this:
>>
>> static int veth_select_txq(struct net_device *dev)
>> {
>> return smp_processor_id() % dev->real_num_tx_queues;
>> }
>>
>> static int veth_xdp_xmit(struct net_device *dev, int n,
>> struct xdp_frame **frames, u32 flags)
>> {
>> ...
>> txq = veth_select_txq(dev);
>> rcv_rxq = txq; // 1-to-1 mapping from txq to peer rxq
>> // Note: when XDP is enabled on rcv, this condition is always false
>> if (rcv_rxq >= rcv->real_num_rx_queues)
>> return -ENXIO;
>> rcv_priv = netdev_priv(rcv);
>> rq = &rcv_priv->rq[rcv_rxq];
>> ...
>> // account txq stats in some way here
>> }
>
> actually I have a different idea..what about account tx stats on the peer rx
> queue as a result of XDP_TX or ndo_xdp_xmit and properly report this info in
> the ethool stats? In this way we do not have any locking issue and we still use
> the per-queue stats approach. Could you please take a look to the following patch?
Thanks I think your idea is nice.
> diff --git a/drivers/net/veth.c b/drivers/net/veth.c
> index b6505a6c7102..f2acd2ee6287 100644
> --- a/drivers/net/veth.c
> +++ b/drivers/net/veth.c
> @@ -92,17 +92,22 @@ struct veth_q_stat_desc {
> static const struct veth_q_stat_desc veth_rq_stats_desc[] = {
> { "xdp_packets", VETH_RQ_STAT(xdp_packets) },
> { "xdp_bytes", VETH_RQ_STAT(xdp_bytes) },
> - { "rx_drops", VETH_RQ_STAT(rx_drops) },
> - { "rx_xdp_redirect", VETH_RQ_STAT(xdp_redirect) },
> - { "rx_xdp_drops", VETH_RQ_STAT(xdp_drops) },
> - { "rx_xdp_tx", VETH_RQ_STAT(xdp_tx) },
> - { "rx_xdp_tx_errors", VETH_RQ_STAT(xdp_tx_err) },
> - { "tx_xdp_xmit", VETH_RQ_STAT(xdp_xmit) },
> - { "tx_xdp_xmit_errors", VETH_RQ_STAT(xdp_xmit_err) },
> + { "drops", VETH_RQ_STAT(rx_drops) },
> + { "xdp_redirect", VETH_RQ_STAT(xdp_redirect) },
> + { "xdp_drops", VETH_RQ_STAT(xdp_drops) },
> };
>
> #define VETH_RQ_STATS_LEN ARRAY_SIZE(veth_rq_stats_desc)
>
> +static const struct veth_q_stat_desc veth_tq_stats_desc[] = {
> + { "xdp_tx", VETH_RQ_STAT(xdp_tx) },
> + { "xdp_tx_errors", VETH_RQ_STAT(xdp_tx_err) },
I'm wondering why xdp_tx is not accounted in rx_queue?
You can count xdp_tx/tx_error somewhere in rx path like veth_xdp_flush_bq().
xdp_redirect and xdp_drops are similar actions and in rx stats.
> + { "xdp_xmit", VETH_RQ_STAT(xdp_xmit) },
> + { "xdp_xmit_errors", VETH_RQ_STAT(xdp_xmit_err) },
> +};
> +
> +#define VETH_TQ_STATS_LEN ARRAY_SIZE(veth_tq_stats_desc)
> +
> static struct {
> const char string[ETH_GSTRING_LEN];
> } ethtool_stats_keys[] = {
> @@ -142,6 +147,14 @@ static void veth_get_strings(struct net_device *dev, u32 stringset, u8 *buf)
> p += ETH_GSTRING_LEN;
> }
> }
> + for (i = 0; i < dev->real_num_tx_queues; i++) {
> + for (j = 0; j < VETH_TQ_STATS_LEN; j++) {
> + snprintf(p, ETH_GSTRING_LEN,
> + "tx_queue_%u_%.18s",
> + i, veth_tq_stats_desc[j].desc);
> + p += ETH_GSTRING_LEN;
> + }
> + }
> break;
> }
> }
> @@ -151,7 +164,8 @@ static int veth_get_sset_count(struct net_device *dev, int sset)
> switch (sset) {
> case ETH_SS_STATS:
> return ARRAY_SIZE(ethtool_stats_keys) +
> - VETH_RQ_STATS_LEN * dev->real_num_rx_queues;
> + VETH_RQ_STATS_LEN * dev->real_num_rx_queues +
> + VETH_TQ_STATS_LEN * dev->real_num_tx_queues;
> default:
> return -EOPNOTSUPP;
> }
> @@ -160,7 +174,7 @@ static int veth_get_sset_count(struct net_device *dev, int sset)
> static void veth_get_ethtool_stats(struct net_device *dev,
> struct ethtool_stats *stats, u64 *data)
> {
> - struct veth_priv *priv = netdev_priv(dev);
> + struct veth_priv *rcv_priv, *priv = netdev_priv(dev);
> struct net_device *peer = rtnl_dereference(priv->peer);
> int i, j, idx;
>
> @@ -181,6 +195,26 @@ static void veth_get_ethtool_stats(struct net_device *dev,
> } while (u64_stats_fetch_retry_irq(&rq_stats->syncp, start));
> idx += VETH_RQ_STATS_LEN;
> }
> +
> + if (!peer)
> + return;
> +
> + rcv_priv = netdev_priv(peer);
> + for (i = 0; i < peer->real_num_rx_queues; i++) {
> + const struct veth_rq_stats *rq_stats = &rcv_priv->rq[i].stats;
> + const void *stats_base = (void *)&rq_stats->vs;
> + unsigned int start, tx_idx;
> + size_t offset;
> +
> + tx_idx = (i % dev->real_num_tx_queues) * VETH_TQ_STATS_LEN;
I'm a bit concerned that this can fold multiple rx queue counters into one tx
counter. But I cannot think of a better idea provided that we want to align XDP
stats between drivers. So I'm OK with this.
Toshiaki Makita
> + do {
> + start = u64_stats_fetch_begin_irq(&rq_stats->syncp);
> + for (j = 0; j < VETH_TQ_STATS_LEN; j++) {
> + offset = veth_tq_stats_desc[j].offset;
> + data[tx_idx + idx + j] += *(u64 *)(stats_base + offset);
> + }
> + } while (u64_stats_fetch_retry_irq(&rq_stats->syncp, start));
> + }
> }
>
> static const struct ethtool_ops veth_ethtool_ops = {
> @@ -340,8 +374,7 @@ static void veth_get_stats64(struct net_device *dev,
> tot->tx_packets = packets;
>
> veth_stats_rx(&rx, dev);
> - tot->tx_dropped += rx.xdp_xmit_err + rx.xdp_tx_err;
> - tot->rx_dropped = rx.rx_drops;
> + tot->rx_dropped = rx.rx_drops + rx.xdp_tx_err + rx.xdp_xmit_err;
> tot->rx_bytes = rx.xdp_bytes;
> tot->rx_packets = rx.xdp_packets;
>
> @@ -353,7 +386,7 @@ static void veth_get_stats64(struct net_device *dev,
> tot->rx_packets += packets;
>
> veth_stats_rx(&rx, peer);
> - tot->rx_dropped += rx.xdp_xmit_err + rx.xdp_tx_err;
> + tot->tx_dropped += rx.xdp_xmit_err + rx.xdp_tx_err;
> tot->tx_bytes += rx.xdp_bytes;
> tot->tx_packets += rx.xdp_packets;
> }
> @@ -394,9 +427,9 @@ static int veth_xdp_xmit(struct net_device *dev, int n,
> u32 flags, bool ndo_xmit)
> {
> struct veth_priv *rcv_priv, *priv = netdev_priv(dev);
> - unsigned int qidx, max_len;
> struct net_device *rcv;
> int i, ret, drops = n;
> + unsigned int max_len;
> struct veth_rq *rq;
>
> rcu_read_lock();
> @@ -414,8 +447,7 @@ static int veth_xdp_xmit(struct net_device *dev, int n,
> }
>
> rcv_priv = netdev_priv(rcv);
> - qidx = veth_select_rxq(rcv);
> - rq = &rcv_priv->rq[qidx];
> + rq = &rcv_priv->rq[veth_select_rxq(rcv)];
> /* Non-NULL xdp_prog ensures that xdp_ring is initialized on receive
> * side. This means an XDP program is loaded on the peer and the peer
> * device is up.
> @@ -446,7 +478,6 @@ static int veth_xdp_xmit(struct net_device *dev, int n,
>
> ret = n - drops;
> drop:
> - rq = &priv->rq[qidx];
> u64_stats_update_begin(&rq->stats.syncp);
> if (ndo_xmit) {
> rq->stats.vs.xdp_xmit += n - drops;
>
>>
>> Thoughts?
>>
>> Toshiaki Makita
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