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Date: Mon, 12 Nov 2018 15:37:16 -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 v2] net: Add trace events for all receive exit points
----- On Nov 12, 2018, at 3:20 PM, Mathieu Desnoyers mathieu.desnoyers@...icios.com wrote:
> ----- On Nov 12, 2018, at 3:09 PM, Mathieu Desnoyers
> mathieu.desnoyers@...icios.com wrote:
>
>> ----- On Nov 12, 2018, at 2:44 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 discussed over IRC, it is _possible_ to use kretprobes to instrument
>> the exit, but it is not practical. A v3 will be sent soon to clarify
>> this part of the commit message.
>>
>> Also, I wonder if we should use "net_dev_template_exit" for the event
>> class rather than "net_dev_template_return" ?
>
> Hrm, looking at this again, I notice that there is a single DEFINE_EVENT
> using net_dev_template_simple.
>
> We could simply turn netif_receive_skb_list_exit into a TRACE_EVENT(),
> remove the net_dev_template_simple, and rename the net_dev_template_return
> to net_dev_template ?
>
> It's pretty clear from the prototype that it expects a "ret" argument,
> so I don't see the need to also state it in the template name.
As you pointed out on IRC, net_dev_template already exists. So we can
use "net_dev_rx_exit_template" which is along the same lines as
its entry counterpart "net_dev_rx_verbose_template".
Thanks,
Mathieu
>
> Thanks,
>
> Mathieu
>
>>
>> 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>
>>> ---
>>> Changes in v2:
>>> - Add the return value to tracepoints where applicable
>>> - Verify if tracepoint is enabled before walking list in
>>> netif_receive_skb_list
>>> ---
>>> include/trace/events/net.h | 78 ++++++++++++++++++++++++++++++++++++++
>>> net/core/dev.c | 38 ++++++++++++++++---
>>> 2 files changed, 110 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/include/trace/events/net.h b/include/trace/events/net.h
>>> index 00aa72ce0e7c..cff1a7b9d0bb 100644
>>> --- a/include/trace/events/net.h
>>> +++ b/include/trace/events/net.h
>>> @@ -117,6 +117,42 @@ DECLARE_EVENT_CLASS(net_dev_template,
>>> __get_str(name), __entry->skbaddr, __entry->len)
>>> )
>>>
>>> +DECLARE_EVENT_CLASS(net_dev_template_return,
>>> +
>>> + TP_PROTO(struct sk_buff *skb, int ret),
>>> +
>>> + TP_ARGS(skb, ret),
>>> +
>>> + TP_STRUCT__entry(
>>> + __field(void *, skbaddr)
>>> + __field(int, ret)
>>> + ),
>>> +
>>> + TP_fast_assign(
>>> + __entry->skbaddr = skb;
>>> + __entry->ret = ret;
>>> + ),
>>> +
>>> + TP_printk("skbaddr=%p ret=%d", __entry->skbaddr, __entry->ret)
>>> +)
>>> +
>>> +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 +280,48 @@ DEFINE_EVENT(net_dev_rx_verbose_template,
>>> netif_rx_ni_entry,
>>> TP_ARGS(skb)
>>> );
>>>
>>> +DEFINE_EVENT(net_dev_template_return, napi_gro_frags_exit,
>>> +
>>> + TP_PROTO(struct sk_buff *skb, int ret),
>>> +
>>> + TP_ARGS(skb, ret)
>>> +);
>>> +
>>> +DEFINE_EVENT(net_dev_template_return, napi_gro_receive_exit,
>>> +
>>> + TP_PROTO(struct sk_buff *skb, int ret),
>>> +
>>> + TP_ARGS(skb, ret)
>>> +);
>>> +
>>> +DEFINE_EVENT(net_dev_template_return, netif_receive_skb_exit,
>>> +
>>> + TP_PROTO(struct sk_buff *skb, int ret),
>>> +
>>> + TP_ARGS(skb, ret)
>>> +);
>>> +
>>> +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_return, netif_rx_exit,
>>> +
>>> + TP_PROTO(struct sk_buff *skb, int ret),
>>> +
>>> + TP_ARGS(skb, ret)
>>> +);
>>> +
>>> +DEFINE_EVENT(net_dev_template_return, netif_rx_ni_exit,
>>> +
>>> + TP_PROTO(struct sk_buff *skb, int ret),
>>> +
>>> + TP_ARGS(skb, ret)
>>> +);
>>> +
>>> #endif /* _TRACE_NET_H */
>>>
>>> /* This part must be outside protection */
>>> diff --git a/net/core/dev.c b/net/core/dev.c
>>> index 0ffcbdd55fa9..c4dc5df34abe 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, ret);
>>> +
>>> + 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, err);
>>>
>>> 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, ret);
>>> +
>>> + return ret;
>>> }
>>> EXPORT_SYMBOL(netif_receive_skb);
>>>
>>> @@ -5244,9 +5255,15 @@ void netif_receive_skb_list(struct list_head *head)
>>>
>>> if (list_empty(head))
>>> return;
>>> - list_for_each_entry(skb, head, list)
>>> - trace_netif_receive_skb_list_entry(skb);
>>> + if (trace_netif_receive_skb_list_entry_enabled()) {
>>> + list_for_each_entry(skb, head, list)
>>> + trace_netif_receive_skb_list_entry(skb);
>>> + }
>>> netif_receive_skb_list_internal(head);
>>> + if (trace_netif_receive_skb_list_exit_enabled()) {
>>> + list_for_each_entry(skb, head, list)
>>> + trace_netif_receive_skb_list_exit(skb);
>>> + }
>>> }
>>> EXPORT_SYMBOL(netif_receive_skb_list);
>>>
>>> @@ -5634,12 +5651,17 @@ 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, ret);
>>> +
>>> + return ret;
>>> }
>>> EXPORT_SYMBOL(napi_gro_receive);
>>>
>>> @@ -5753,6 +5775,7 @@ 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 +5783,10 @@ 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, ret);
>>> +
>>> + return ret;
>>> }
>>> EXPORT_SYMBOL(napi_gro_frags);
>>>
>>> --
>>> 2.19.1
>>
>> --
>> Mathieu Desnoyers
>> EfficiOS Inc.
>> http://www.efficios.com
>
> --
> Mathieu Desnoyers
> EfficiOS Inc.
> http://www.efficios.com
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
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