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Message-ID: <1057796879.2336.1541708744442.JavaMail.zimbra@efficios.com>
Date: Thu, 8 Nov 2018 15:25:44 -0500 (EST)
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Geneviève Bastien <gbastien@...satic.net>
Cc: "David S. Miller" <davem@...emloft.net>,
netdev <netdev@...r.kernel.org>, rostedt <rostedt@...dmis.org>,
Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH] net: Add trace events for all receive exit points
----- On Nov 8, 2018, at 2:56 PM, Geneviève Bastien gbastien@...satic.net wrote:
> Trace events are already present for the receive entry points, to indicate
> how the reception entered the stack.
>
> This patch adds the corresponding exit trace events that will bound the
> reception such that all events occurring between the entry and the exit
> can be considered as part of the reception context. This greatly helps
> for dependency and root cause analyses.
>
> Without this, it is impossible to determine whether a sched_wakeup
> event following a netif_receive_skb event is the result of the packet
> reception or a simple coincidence after further processing by the
> thread.
As a clarification: it is indeed not possible with tracepoint instrumentation,
which I think is your point here. It might be possible to do so by using other
mechanisms like kretprobes, but considering that the "entry" point was deemed
important enough to have a tracepoint, it would be good to add the matching exit
events.
Being able to link the packet reception entry/exit with wakeups is key to
allow tools to perform automated network stack latency analysis, so I think
the use case justifies adding the missing "exit" events.
It might be great if you can provide a glimpse of the wakeup dependency chain
analysis prototypes you have created, which rely on this new event, in order
to justify adding it.
Thanks,
Mathieu
>
> Signed-off-by: Geneviève Bastien <gbastien@...satic.net>
> CC: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> CC: Steven Rostedt <rostedt@...dmis.org>
> CC: Ingo Molnar <mingo@...hat.com>
> CC: David S. Miller <davem@...emloft.net>
> ---
> include/trace/events/net.h | 59 ++++++++++++++++++++++++++++++++++++++
> net/core/dev.c | 30 ++++++++++++++++---
> 2 files changed, 85 insertions(+), 4 deletions(-)
>
> diff --git a/include/trace/events/net.h b/include/trace/events/net.h
> index 00aa72ce0e7c..318307511018 100644
> --- a/include/trace/events/net.h
> +++ b/include/trace/events/net.h
> @@ -117,6 +117,23 @@ DECLARE_EVENT_CLASS(net_dev_template,
> __get_str(name), __entry->skbaddr, __entry->len)
> )
>
> +DECLARE_EVENT_CLASS(net_dev_template_simple,
> +
> + TP_PROTO(struct sk_buff *skb),
> +
> + TP_ARGS(skb),
> +
> + TP_STRUCT__entry(
> + __field(void *, skbaddr)
> + ),
> +
> + TP_fast_assign(
> + __entry->skbaddr = skb;
> + ),
> +
> + TP_printk("skbaddr=%p", __entry->skbaddr)
> +)
> +
> DEFINE_EVENT(net_dev_template, net_dev_queue,
>
> TP_PROTO(struct sk_buff *skb),
> @@ -244,6 +261,48 @@ DEFINE_EVENT(net_dev_rx_verbose_template,
> netif_rx_ni_entry,
> TP_ARGS(skb)
> );
>
> +DEFINE_EVENT(net_dev_template_simple, napi_gro_frags_exit,
> +
> + TP_PROTO(struct sk_buff *skb),
> +
> + TP_ARGS(skb)
> +);
> +
> +DEFINE_EVENT(net_dev_template_simple, napi_gro_receive_exit,
> +
> + TP_PROTO(struct sk_buff *skb),
> +
> + TP_ARGS(skb)
> +);
> +
> +DEFINE_EVENT(net_dev_template_simple, netif_receive_skb_exit,
> +
> + TP_PROTO(struct sk_buff *skb),
> +
> + TP_ARGS(skb)
> +);
> +
> +DEFINE_EVENT(net_dev_template_simple, netif_receive_skb_list_exit,
> +
> + TP_PROTO(struct sk_buff *skb),
> +
> + TP_ARGS(skb)
> +);
> +
> +DEFINE_EVENT(net_dev_template_simple, netif_rx_exit,
> +
> + TP_PROTO(struct sk_buff *skb),
> +
> + TP_ARGS(skb)
> +);
> +
> +DEFINE_EVENT(net_dev_template_simple, netif_rx_ni_exit,
> +
> + TP_PROTO(struct sk_buff *skb),
> +
> + TP_ARGS(skb)
> +);
> +
> #endif /* _TRACE_NET_H */
>
> /* This part must be outside protection */
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 0ffcbdd55fa9..e670ca27e829 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -4520,9 +4520,14 @@ static int netif_rx_internal(struct sk_buff *skb)
>
> int netif_rx(struct sk_buff *skb)
> {
> + int ret;
> +
> trace_netif_rx_entry(skb);
>
> - return netif_rx_internal(skb);
> + ret = netif_rx_internal(skb);
> + trace_netif_rx_exit(skb);
> +
> + return ret;
> }
> EXPORT_SYMBOL(netif_rx);
>
> @@ -4537,6 +4542,7 @@ int netif_rx_ni(struct sk_buff *skb)
> if (local_softirq_pending())
> do_softirq();
> preempt_enable();
> + trace_netif_rx_ni_exit(skb);
>
> return err;
> }
> @@ -5222,9 +5228,14 @@ static void netif_receive_skb_list_internal(struct
> list_head *head)
> */
> int netif_receive_skb(struct sk_buff *skb)
> {
> + int ret;
> +
> trace_netif_receive_skb_entry(skb);
>
> - return netif_receive_skb_internal(skb);
> + ret = netif_receive_skb_internal(skb);
> + trace_netif_receive_skb_exit(skb);
> +
> + return ret;
> }
> EXPORT_SYMBOL(netif_receive_skb);
>
> @@ -5247,6 +5258,8 @@ void netif_receive_skb_list(struct list_head *head)
> list_for_each_entry(skb, head, list)
> trace_netif_receive_skb_list_entry(skb);
> netif_receive_skb_list_internal(head);
> + list_for_each_entry(skb, head, list)
> + trace_netif_receive_skb_list_exit(skb);
> }
> EXPORT_SYMBOL(netif_receive_skb_list);
>
> @@ -5634,12 +5647,17 @@ static gro_result_t napi_skb_finish(gro_result_t ret,
> struct sk_buff *skb)
>
> gro_result_t napi_gro_receive(struct napi_struct *napi, struct sk_buff *skb)
> {
> + gro_result_t ret;
> +
> skb_mark_napi_id(skb, napi);
> trace_napi_gro_receive_entry(skb);
>
> skb_gro_reset_offset(skb);
>
> - return napi_skb_finish(dev_gro_receive(napi, skb), skb);
> + ret = napi_skb_finish(dev_gro_receive(napi, skb), skb);
> + trace_napi_gro_receive_exit(skb);
> +
> + return ret;
> }
> EXPORT_SYMBOL(napi_gro_receive);
>
> @@ -5753,6 +5771,7 @@ static struct sk_buff *napi_frags_skb(struct napi_struct
> *napi)
>
> gro_result_t napi_gro_frags(struct napi_struct *napi)
> {
> + gro_result_t ret;
> struct sk_buff *skb = napi_frags_skb(napi);
>
> if (!skb)
> @@ -5760,7 +5779,10 @@ gro_result_t napi_gro_frags(struct napi_struct *napi)
>
> trace_napi_gro_frags_entry(skb);
>
> - return napi_frags_finish(napi, skb, dev_gro_receive(napi, skb));
> + ret = napi_frags_finish(napi, skb, dev_gro_receive(napi, skb));
> + trace_napi_gro_frags_exit(skb);
> +
> + return ret;
> }
> EXPORT_SYMBOL(napi_gro_frags);
>
> --
> 2.19.1
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
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