netdev - Re: [PATCH v4] net: Add trace events for all receive exit points

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Message-Id: <20181130.132321.418162208729355308.davem@davemloft.net>
Date:   Fri, 30 Nov 2018 13:23:21 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     gbastien@...satic.net
Cc:     netdev@...r.kernel.org, mathieu.desnoyers@...icios.com,
        rostedt@...dmis.org, mingo@...hat.com
Subject: Re: [PATCH v4] net: Add trace events for all receive exit points

From: Geneviève Bastien <gbastien@...satic.net>
Date: Tue, 27 Nov 2018 12:52:39 -0500

> 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 not possible with tracepoint instrumentation 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. It is possible using other mechanisms
> like kretprobes, but considering the "entry" points are already present,
> it would be good to add the matching exit events.
> 
> In addition to linking packets with wakeups, the entry/exit event pair
> can also be used to perform network stack latency analyses.
> 
> 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>
> Reviewed-by: Steven Rostedt (VMware) <rostedt@...dmis.org> (tracing
> side)

Applied to net-next, thanks for sticking with this.