On Mon, 18 Nov 2013, George V. Neville-Neil wrote:
Allow ethernet drivers to pass in packets connected via the nextpkt pointer.
Handling packets in this way allows drivers to amortize work during packet
reception.
Submitted by: Vijay Singh
Sponsored by: NetApp
Currently, it is quite easy to make mistakes regarding individual mbuf chains
vs. lists of mbuf chains. This leads me to wonder whether a new type, perhaps
simply constructed on the stack before passing in, should be used for KPIs
that accept lists of packets. E.g.,
/*
* This structure is almost always allocated on a caller stack, so
* cannot itself be queued without memory allocation in most cases.
*/
struct mbuf_queue {
struct mbuf *mq_head;
};
int
ether_input(struct ifnet *ifp, struct mbuf_queue *m)
{
...
}
...
struct mbuf_queue mq = { m };
return (ether_input(ifp, &mq));
...
That way the compiler can help us figure out where we expect an individual
packet but have accidentally leaked a queue. Functions that accept only a
single packet could also more agressively assert that m->m_nextpkt is NULL:
M_ASSERT_ONEPACKET(m);
Robert
Modified:
head/sys/net/if_ethersubr.c
Modified: head/sys/net/if_ethersubr.c
==============================================================================
--- head/sys/net/if_ethersubr.c Mon Nov 18 22:55:50 2013 (r258327)
+++ head/sys/net/if_ethersubr.c Mon Nov 18 22:58:14 2013 (r258328)
@@ -708,13 +708,25 @@ static void
ether_input(struct ifnet *ifp, struct mbuf *m)
{
+ struct mbuf *mn;
+
/*
- * We will rely on rcvif being set properly in the deferred context,
- * so assert it is correct here.
+ * The drivers are allowed to pass in a chain of packets linked with
+ * m_nextpkt. We split them up into separate packets here and pass
+ * them up. This allows the drivers to amortize the receive lock.
*/
- KASSERT(m->m_pkthdr.rcvif == ifp, ("%s: ifnet mismatch", __func__));
+ while (m) {
+ mn = m->m_nextpkt;
+ m->m_nextpkt = NULL;
- netisr_dispatch(NETISR_ETHER, m);
+ /*
+ * We will rely on rcvif being set properly in the deferred
context,
+ * so assert it is correct here.
+ */
+ KASSERT(m->m_pkthdr.rcvif == ifp, ("%s: ifnet mismatch",
__func__));
+ netisr_dispatch(NETISR_ETHER, m);
+ m = mn;
+ }
}
/*
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