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    SubjectRe: [RFC PATCH v3 4/5] skb: add tracepoints to freeing skb
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    Le mardi 20 juillet 2010 à 09:49 +0900, Koki Sanagi a écrit :
    > [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@jp.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)
    > +
    > +);
    > +
    > TRACE_EVENT(skb_copy_datagram_iovec,
    >
    > TP_PROTO(const struct sk_buff *skb, int len),
    > diff --git a/net/core/datagram.c b/net/core/datagram.c
    > index f5b6f43..1ea32a0 100644
    > --- a/net/core/datagram.c
    > +++ b/net/core/datagram.c
    > @@ -231,6 +231,7 @@ void skb_free_datagram_locked(struct sock *sk, struct sk_buff *skb)
    > {
    > bool slow;
    >
    > + trace_skb_free_datagram_locked(skb);

    Here you unconditionally trace before the test on skb->users

    > if (likely(atomic_read(&skb->users) == 1))
    > smp_rmb();
    > else if (likely(!atomic_dec_and_test(&skb->users)))
    > diff --git a/net/core/dev.c b/net/core/dev.c
    > index 4acfec6..d979847 100644
    > --- a/net/core/dev.c
    > +++ b/net/core/dev.c
    > @@ -131,6 +131,7 @@
    > #include <linux/random.h>
    > #include <trace/events/napi.h>
    > #include <trace/events/net.h>
    > +#include <trace/events/skb.h>
    > #include <linux/pci.h>
    >
    > #include "net-sysfs.h"
    > @@ -1581,6 +1582,7 @@ void dev_kfree_skb_irq(struct sk_buff *skb)
    > struct softnet_data *sd;
    > unsigned long flags;
    >
    > + trace_dev_kfree_skb_irq(skb);
    > local_irq_save(flags);
    > sd = &__get_cpu_var(softnet_data);
    > skb->next = sd->completion_queue;
    > diff --git a/net/core/skbuff.c b/net/core/skbuff.c
    > index 34432b4..a7b4036 100644
    > --- a/net/core/skbuff.c
    > +++ b/net/core/skbuff.c
    > @@ -466,6 +466,7 @@ void consume_skb(struct sk_buff *skb)
    > smp_rmb();
    > else if (likely(!atomic_dec_and_test(&skb->users)))
    > return;

    While here you trace _after_ the test on skb->users - and a "return;" ,
    so you miss some consume_skb() calls


    > + trace_consume_skb(skb);
    > __kfree_skb(skb);
    > }
    > EXPORT_SYMBOL(consume_skb);
    >


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