The drbr(9) API appeared to be so unclear, that most drivers in

tree used it incorrectly, which lead to inaccurate overrated
if_obytes accounting. The drbr(9) used to update ifnet stats on
drbr_enqueue(), which is not accurate since enqueuing doesn't
imply successful processing by driver. Dequeuing neither mean
that. Most drivers also called drbr_stats_update() which did
accounting again, leading to doubled if_obytes statistics. And
in case of severe transmitting, when a packet could be several
times enqueued and dequeued it could have been accounted several
times.

o Thus, make drbr(9) API thinner. Now drbr(9) merely chooses between
  ALTQ queueing or buf_ring(9) queueing.
  - It doesn't touch the buf_ring stats any more.
  - It doesn't touch ifnet stats anymore.
  - drbr_stats_update() no longer exists.

o buf_ring(9) handles its stats itself:
  - It handles br_drops itself.
  - br_prod_bytes stats are dropped. Rationale: no one ever
    reads them but update of a common counter on every packet
    negatively affects performance due to excessive cache
    invalidation.
  - buf_ring_enqueue_bytes() reduced to buf_ring_enqueue(), since
    we no longer account bytes.

o Drivers handle their stats theirselves: if_obytes, if_omcasts.

o mlx4(4), igb(4), em(4), vxge(4), oce(4) and  ixv(4) no longer
  use drbr_stats_update(), and update ifnet stats theirselves.

o bxe(4) was the most correct driver, it didn't call
  drbr_stats_update(), thus it was the only driver accurate under
  moderate load. Now it also maintains stats itself.

o ixgbe(4) had already taken stats from hardware, so just
  - drop software stats updating.
  - take multicast packet count from hardware as well.

o mxge(4) just no longer needs NO_SLOW_STATS define.

o cxgb(4), cxgbe(4) need no change, since they obtain stats
  from hardware.

Reviewed by:	jfv, gnn

1 files changed, 3 insertions, 17 deletions

diff --git a/sys/net/if_var.h b/sys/net/if_var.h
index 01ec2b6..8a1d5cc 100644
--- a/sys/net/if_var.h
+++ b/sys/net/if_var.h
@@ -590,22 +590,10 @@ do {									\
 } while (0)
 
 #ifdef _KERNEL
-static __inline void
-drbr_stats_update(struct ifnet *ifp, int len, int mflags)
-{
-#ifndef NO_SLOW_STATS
-	ifp->if_obytes += len;
-	if (mflags & M_MCAST)
-		ifp->if_omcasts++;
-#endif
-}
-
 static __inline int
 drbr_enqueue(struct ifnet *ifp, struct buf_ring *br, struct mbuf *m)
 {	
 	int error = 0;
-	int len = m->m_pkthdr.len;
-	int mflags = m->m_flags;
 
 #ifdef ALTQ
 	if (ALTQ_IS_ENABLED(&ifp->if_snd)) {
@@ -613,12 +601,10 @@ drbr_enqueue(struct ifnet *ifp, struct buf_ring *br, struct mbuf *m)
 		return (error);
 	}
 #endif
-	if ((error = buf_ring_enqueue_bytes(br, m, len)) == ENOBUFS) {
-		br->br_drops++;
+	error = buf_ring_enqueue(br, m);
+	if (error)
 		m_freem(m);
-	} else
-		drbr_stats_update(ifp, len, mflags);
-	
+
 	return (error);
 }