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qdisc: add tracepoint qdisc:qdisc_dequeue for dequeued SKBs

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The main purpose of this tracepoint is to monitor bulk dequeue
in the network qdisc layer, as it cannot be deducted from the
existing qdisc stats.

The txq_state can be used for determining the reason for zero packet
dequeues, see enum netdev_queue_state_t.

Notice all packets doesn't necessary activate this tracepoint. As
qdiscs with flag TCQ_F_CAN_BYPASS, can directly invoke
sch_direct_xmit() when qdisc_qlen is zero.

Remember that perf record supports filters like:

 perf record -e qdisc:qdisc_dequeue \
  --filter 'ifindex == 4 && (packets > 1 || txq_state > 0)'

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Jesper Dangaard Brouer 2017-08-15 21:11:03 +02:00 committed by David S. Miller
parent 7440cccee0
commit e543002f77
3 changed files with 57 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

50
include/trace/events/qdisc.h Normal file
View File

@ -0,0 +1,50 @@
#undef TRACE_SYSTEM
#define TRACE_SYSTEM qdisc
#if !defined(_TRACE_QDISC_H) || defined(TRACE_HEADER_MULTI_READ)
#define _TRACE_QDISC_H_
#include <linux/skbuff.h>
#include <linux/netdevice.h>
#include <linux/tracepoint.h>
#include <linux/ftrace.h>
TRACE_EVENT(qdisc_dequeue,
TP_PROTO(struct Qdisc *qdisc, const struct netdev_queue *txq,
int packets, struct sk_buff *skb),
TP_ARGS(qdisc, txq, packets, skb),
TP_STRUCT__entry(
__field( struct Qdisc *, qdisc )
__field(const struct netdev_queue *, txq )
__field( int, packets )
__field( void *, skbaddr )
__field( int, ifindex )
__field( u32, handle )
__field( u32, parent )
__field( unsigned long, txq_state)
),
/* skb==NULL indicate packets dequeued was 0, even when packets==1 */
TP_fast_assign(
__entry->qdisc = qdisc;
__entry->txq = txq;
__entry->packets = skb ? packets : 0;
__entry->skbaddr = skb;
__entry->ifindex = txq->dev ? txq->dev->ifindex : 0;
__entry->handle = qdisc->handle;
__entry->parent = qdisc->parent;
__entry->txq_state = txq->state;
),
TP_printk("dequeue ifindex=%d qdisc handle=0x%X parent=0x%X txq_state=0x%lX packets=%d skbaddr=%p",
__entry->ifindex, __entry->handle, __entry->parent,
__entry->txq_state, __entry->packets, __entry->skbaddr )
);
#endif /* _TRACE_QDISC_H_ */
/* This part must be outside protection */
#include <trace/define_trace.h>

1
net/core/net-traces.c
View File

@ -32,6 +32,7 @@
#include <trace/events/sock.h>
#include <trace/events/udp.h>
#include <trace/events/fib.h>
#include <trace/events/qdisc.h>
#if IS_ENABLED(CONFIG_IPV6)
#include <trace/events/fib6.h>
EXPORT_TRACEPOINT_SYMBOL_GPL(fib6_table_lookup);

8
net/sched/sch_generic.c
View File

@ -29,6 +29,7 @@
#include <net/sch_generic.h>
#include <net/pkt_sched.h>
#include <net/dst.h>
#include <trace/events/qdisc.h>
/* Qdisc to use by default */
const struct Qdisc_ops *default_qdisc_ops = &pfifo_fast_ops;
@ -126,7 +127,7 @@ static struct sk_buff *dequeue_skb(struct Qdisc *q, bool *validate,
q->q.qlen--;
} else
skb = NULL;
return skb;
goto trace;
}
*validate = true;
skb = q->skb_bad_txq;
@ -139,7 +140,8 @@ static struct sk_buff *dequeue_skb(struct Qdisc *q, bool *validate,
q->q.qlen--;
goto bulk;
}
return NULL;
skb = NULL;
goto trace;
}
if (!(q->flags & TCQ_F_ONETXQUEUE) ||
!netif_xmit_frozen_or_stopped(txq))
@ -151,6 +153,8 @@ bulk:
else
try_bulk_dequeue_skb_slow(q, skb, packets);
}
trace:
trace_qdisc_dequeue(q, txq, *packets, skb);
return skb;
}