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    Subject[PATCH v4 4/5] skb: add tracepoints to freeing skb
    This patch adds tracepoint to consume_skb and add trace_kfree_skb before
    __kfree_skb in skb_free_datagram_locked and net_tx_action.
    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.

    sshd-6828 [000] 112689.258154: consume_skb: skbaddr=f2d99bb8

    Signed-off-by: Koki Sanagi <sanagi.koki@jp.fujitsu.com>
    ---
    include/trace/events/skb.h | 17 +++++++++++++++++
    net/core/datagram.c | 1 +
    net/core/dev.c | 2 ++
    net/core/skbuff.c | 1 +
    4 files changed, 21 insertions(+), 0 deletions(-)

    diff --git a/include/trace/events/skb.h b/include/trace/events/skb.h
    index 4b2be6d..75ce9d5 100644
    --- a/include/trace/events/skb.h
    +++ b/include/trace/events/skb.h
    @@ -35,6 +35,23 @@ TRACE_EVENT(kfree_skb,
    __entry->skbaddr, __entry->protocol, __entry->location)
    );

    +TRACE_EVENT(consume_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)
    +);
    +
    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 251997a..282806b 100644
    --- a/net/core/datagram.c
    +++ b/net/core/datagram.c
    @@ -243,6 +243,7 @@ void skb_free_datagram_locked(struct sock *sk, struct sk_buff *skb)
    unlock_sock_fast(sk, slow);

    /* skb is now orphaned, can be freed outside of locked section */
    + trace_kfree_skb(skb, skb_free_datagram_locked);
    __kfree_skb(skb);
    }
    EXPORT_SYMBOL(skb_free_datagram_locked);
    diff --git a/net/core/dev.c b/net/core/dev.c
    index c9b026a..48f7977 100644
    --- a/net/core/dev.c
    +++ b/net/core/dev.c
    @@ -129,6 +129,7 @@
    #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"
    @@ -2589,6 +2590,7 @@ static void net_tx_action(struct softirq_action *h)
    clist = clist->next;

    WARN_ON(atomic_read(&skb->users));
    + trace_kfree_skb(skb, net_tx_action);
    __kfree_skb(skb);
    }
    }
    diff --git a/net/core/skbuff.c b/net/core/skbuff.c
    index 99ef721..ef4ffa8 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;
    + trace_consume_skb(skb);
    __kfree_skb(skb);
    }
    EXPORT_SYMBOL(consume_skb);


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