netdev - Re: [RFC PATCH v3 4/5] skb: add tracepoints to freeing skb

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Message-ID: <20100720115044.GD1995@hmsreliant.think-freely.org>
Date:	Tue, 20 Jul 2010 07:50:44 -0400
From:	Neil Horman <nhorman@...driver.com>
To:	Koki Sanagi <sanagi.koki@...fujitsu.com>
Cc:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	davem@...emloft.net, kaneshige.kenji@...fujitsu.com,
	izumi.taku@...fujitsu.com, kosaki.motohiro@...fujitsu.com,
	laijs@...fujitsu.com, scott.a.mcmillan@...el.com,
	rostedt@...dmis.org, eric.dumazet@...il.com, fweisbec@...il.com,
	mathieu.desnoyers@...ymtl.ca
Subject: Re: [RFC PATCH v3 4/5] skb: add tracepoints to freeing skb

On Tue, Jul 20, 2010 at 09:49:10AM +0900, Koki Sanagi wrote:
> [RFC PATCH v3 4/5] skb: add tracepoints to freeing skb
> This patch adds tracepoint to consume_skb, dev_kfree_skb_irq and
> skb_free_datagram_locked. Combinating with tracepoint on dev_hard_start_xmit,
> we can check how long it takes to free transmited packets. And using it, we can
> calculate how many packets driver had at that time. It is useful when a drop of
> transmited packet is a problem.
> 
>           <idle>-0     [001] 241409.218333: consume_skb: skbaddr=dd6b2fb8
>           <idle>-0     [001] 241409.490555: dev_kfree_skb_irq: skbaddr=f5e29840
> 
>         udp-recv-302   [001] 515031.206008: skb_free_datagram_locked: skbaddr=f5b1d900
> 
> 
> Signed-off-by: Koki Sanagi <sanagi.koki@...fujitsu.com>
> ---
>  include/trace/events/skb.h |   42 ++++++++++++++++++++++++++++++++++++++++++
>  net/core/datagram.c        |    1 +
>  net/core/dev.c             |    2 ++
>  net/core/skbuff.c          |    1 +
>  4 files changed, 46 insertions(+), 0 deletions(-)
> 
> diff --git a/include/trace/events/skb.h b/include/trace/events/skb.h
> index 4b2be6d..84c9041 100644
> --- a/include/trace/events/skb.h
> +++ b/include/trace/events/skb.h
> @@ -35,6 +35,48 @@ TRACE_EVENT(kfree_skb,
>  		__entry->skbaddr, __entry->protocol, __entry->location)
>  );
>  
> +DECLARE_EVENT_CLASS(free_skb,
> +
> +	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(free_skb, consume_skb,
> +
> +	TP_PROTO(struct sk_buff *skb),
> +
> +	TP_ARGS(skb)
> +
> +);
> +
> +DEFINE_EVENT(free_skb, dev_kfree_skb_irq,
> +
> +	TP_PROTO(struct sk_buff *skb),
> +
> +	TP_ARGS(skb)
> +
> +);
> +
> +DEFINE_EVENT(free_skb, skb_free_datagram_locked,
> +
> +	TP_PROTO(struct sk_buff *skb),
> +
> +	TP_ARGS(skb)
> +
> +);
> +

Why create these last two tracepoints at all?  dev_kfree_skb_irq will eventually
pass through kfree_skb anyway, getting picked up by the tracepoint there, the
while the latter won't (since it uses __kfree_skb instead), I think that could
be fixed up by add a call to trace_kfree_skb there directly, saving you two
tracepoints.

Neil

> 
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