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qdisc: add tracepoint qdisc:qdisc_dequeue for dequeued SKBs 

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;
}