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Date: Thu, 15 Jul 2021 19:24:25 +0800
From: Yunsheng Lin <linyunsheng@...wei.com>
To: Cong Wang <xiyou.wangcong@...il.com>, <netdev@...r.kernel.org>
CC: Qitao Xu <qitao.xu@...edance.com>,
Cong Wang <cong.wang@...edance.com>
Subject: Re: [Patch net-next v3] net_sched: introduce tracepoint
trace_qdisc_enqueue()
On 2021/7/15 14:03, Cong Wang wrote:
> From: Qitao Xu <qitao.xu@...edance.com>
>
> Tracepoint trace_qdisc_enqueue() is introduced to trace skb at
> the entrance of TC layer on TX side. This is similar to
> trace_qdisc_dequeue():
>
> 1. For both we only trace successful cases. The failure cases
> can be traced via trace_kfree_skb().
>
> 2. They are called at entrance or exit of TC layer, not for each
> ->enqueue() or ->dequeue(). This is intentional, because
> we want to make trace_qdisc_enqueue() symmetric to
> trace_qdisc_dequeue(), which is easier to use.
>
> The return value of qdisc_enqueue() is not interesting here,
> we have Qdisc's drop packets in ->dequeue(), it is impossible to
> trace them even if we have the return value, the only way to trace
> them is tracing kfree_skb().
>
> We only add information we need to trace ring buffer. If any other
> information is needed, it is easy to extend it without breaking ABI,
> see commit 3dd344ea84e1 ("net: tracepoint: exposing sk_family in all
> tcp:tracepoints").
>
> Reviewed-by: Cong Wang <cong.wang@...edance.com>
> Signed-off-by: Qitao Xu <qitao.xu@...edance.com>
> ---
> v3: expand changelog
> add helper dev_qdisc_enqueue()
>
> v2: improve changelog
>
> include/trace/events/qdisc.h | 26 ++++++++++++++++++++++++++
> net/core/dev.c | 20 ++++++++++++++++----
> 2 files changed, 42 insertions(+), 4 deletions(-)
>
> diff --git a/include/trace/events/qdisc.h b/include/trace/events/qdisc.h
> index 58209557cb3a..c3006c6b4a87 100644
> --- a/include/trace/events/qdisc.h
> +++ b/include/trace/events/qdisc.h
> @@ -46,6 +46,32 @@ TRACE_EVENT(qdisc_dequeue,
> __entry->txq_state, __entry->packets, __entry->skbaddr )
> );
>
> +TRACE_EVENT(qdisc_enqueue,
> +
> + TP_PROTO(struct Qdisc *qdisc, const struct netdev_queue *txq, struct sk_buff *skb),
> +
> + TP_ARGS(qdisc, txq, skb),
> +
> + TP_STRUCT__entry(
> + __field(struct Qdisc *, qdisc)
> + __field(void *, skbaddr)
> + __field(int, ifindex)
> + __field(u32, handle)
> + __field(u32, parent)
> + ),
> +
> + TP_fast_assign(
> + __entry->qdisc = qdisc;
> + __entry->skbaddr = skb;
> + __entry->ifindex = txq->dev ? txq->dev->ifindex : 0;
> + __entry->handle = qdisc->handle;
> + __entry->parent = qdisc->parent;
> + ),
> +
> + TP_printk("enqueue ifindex=%d qdisc handle=0x%X parent=0x%X skbaddr=%px",
> + __entry->ifindex, __entry->handle, __entry->parent, __entry->skbaddr)
> +);
> +
> TRACE_EVENT(qdisc_reset,
>
> TP_PROTO(struct Qdisc *q),
> diff --git a/net/core/dev.c b/net/core/dev.c
> index c253c2aafe97..0dcddd077d60 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -131,6 +131,7 @@
> #include <trace/events/napi.h>
> #include <trace/events/net.h>
> #include <trace/events/skb.h>
> +#include <trace/events/qdisc.h>
> #include <linux/inetdevice.h>
> #include <linux/cpu_rmap.h>
> #include <linux/static_key.h>
> @@ -3844,6 +3845,18 @@ static void qdisc_pkt_len_init(struct sk_buff *skb)
> }
> }
>
> +static int dev_qdisc_enqueue(struct sk_buff *skb, struct Qdisc *q,
> + struct sk_buff **to_free,
> + struct netdev_queue *txq)
> +{
> + int rc;
> +
> + rc = q->enqueue(skb, q, to_free) & NET_XMIT_MASK;
> + if (rc == NET_XMIT_SUCCESS)
I do not really understand the usecase you metioned previously,
but tracepointing the rc in trace_qdisc_enqueue() will avoid the
above checking, which is in the fast path.
If there is no extra checking overhead when this tracepoint is
disabled, then ignore my comment.
> + trace_qdisc_enqueue(q, txq, skb);
> + return rc;
> +}
> +
> static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q,
> struct net_device *dev,
> struct netdev_queue *txq)
> @@ -3862,8 +3875,7 @@ static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q,
> * of q->seqlock to protect from racing with requeuing.
> */
> if (unlikely(!nolock_qdisc_is_empty(q))) {
> - rc = q->enqueue(skb, q, &to_free) &
> - NET_XMIT_MASK;
> + rc = dev_qdisc_enqueue(skb, q, &to_free, txq);
> __qdisc_run(q);
> qdisc_run_end(q);
>
> @@ -3879,7 +3891,7 @@ static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q,
> return NET_XMIT_SUCCESS;
> }
>
> - rc = q->enqueue(skb, q, &to_free) & NET_XMIT_MASK;
> + rc = dev_qdisc_enqueue(skb, q, &to_free, txq);
> qdisc_run(q);
>
> no_lock_out:
> @@ -3923,7 +3935,7 @@ static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q,
> qdisc_run_end(q);
> rc = NET_XMIT_SUCCESS;
> } else {
> - rc = q->enqueue(skb, q, &to_free) & NET_XMIT_MASK;
> + rc = dev_qdisc_enqueue(skb, q, &to_free, txq);
> if (qdisc_run_begin(q)) {
> if (unlikely(contended)) {
> spin_unlock(&q->busylock);
>
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