2012-01-30 21:02:25 +00:00
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.\" Copyright (c) 2009 Bitgravity Inc
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.\" Written by: Kip Macy <kmacy@@FreeBSD.org>
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.\" All rights reserved.
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.\"
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.\" $FreeBSD$
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.\"
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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
2012-09-28 18:28:27 +00:00
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.Dd September 27, 2012
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2012-01-30 21:02:25 +00:00
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.Dt DRBR 9
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.Os
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.Sh NAME
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.Nm drbr ,
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.Nm drbr_free ,
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.Nm drbr_enqueue ,
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.Nm drbr_dequeue ,
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.Nm drbr_dequeue_cond ,
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.Nm drbr_flush ,
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.Nm drbr_empty ,
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.Nm drbr_inuse ,
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.Nd network driver interface to buf_ring
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.Sh SYNOPSIS
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.In sys/param.h
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.In net/if.h
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.In net/if_var.h
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.Ft void
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.Fn drbr_free "struct buf_ring *br" "struct malloc_type *type"
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.Ft int
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.Fn drbr_enqueue "struct ifnet *ifp" "struct buf_ring *br" "struct mbuf *m"
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.Ft struct mbuf *
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.Fn drbr_dequeue "struct ifnet *ifp" "struct buf_ring *br"
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.Ft struct mbuf *
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.Fn drbr_dequeue_cond "struct ifnet *ifp" "struct buf_ring *br" "int (*func) (struct mbuf *, void *)" "void *arg"
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.Ft void
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.Fn drbr_flush "struct ifnet *ifp" "struct buf_ring *br"
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.Ft int
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.Fn drbr_empty "struct ifnet *ifp" "struct buf_ring *br"
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.Ft int
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.Fn drbr_inuse "struct ifnet *ifp" "struct buf_ring *br"
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.Sh DESCRIPTION
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The
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.Nm
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functions provide an API to network drivers for using
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.Xr buf_ring 9
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for enqueueing and dequeueing packets.
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This is meant as a replacement for the IFQ interface for packet queuing.
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It allows a packet to be enqueued with a single atomic and packet
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dequeue to be done without any per-packet atomics as it is protected
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by the driver's tx queue lock.
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If
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.Dv INVARIANTS
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is enabled,
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.Fn drbr_dequeue
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will assert that the tx queue lock is held when it is called.
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.Pp
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The
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2012-03-29 05:02:12 +00:00
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.Fn drbr_free
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2012-01-30 21:02:25 +00:00
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function frees all the enqueued mbufs and then frees the buf_ring.
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.Pp
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The
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.Fn drbr_enqueue
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function is used to enqueue an mbuf to a buf_ring, falling back to the
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ifnet's IFQ if
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.Xr ALTQ 4
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is enabled.
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.Pp
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The
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.Fn drbr_dequeue
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function is used to dequeue an mbuf from a buf_ring or, if
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.Xr ALTQ 4
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is enabled, from the ifnet's IFQ.
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.Pp
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The
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.Fn drbr_dequeue_cond
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function is used to conditionally dequeue an mbuf from a buf_ring based
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on whether
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.Fa func
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returns
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.Dv TRUE
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or
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.Dv FALSE .
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.Pp
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The
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.Fn drbr_flush
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function frees all mbufs enqueued in the buf_ring and the ifnet's IFQ.
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.Pp
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2012-03-29 05:02:12 +00:00
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The
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2012-01-30 21:02:25 +00:00
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.Fn drbr_empty
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function returns
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.Dv TRUE
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if there are no mbufs enqueued,
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.Dv FALSE
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otherwise.
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.Pp
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The
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.Fn drbr_inuse
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function returns the number of mbufs enqueued.
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Note to users that this is intrinsically racy as there is no guarantee that
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2012-03-29 05:02:12 +00:00
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there will not be more mbufs when
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2012-01-30 21:02:25 +00:00
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.Fn drbr_dequeue
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is actually called.
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Provided the tx queue lock is held there will not be less.
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.Sh RETURN VALUES
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The
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.Fn drbr_enqueue
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function returns
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.Er ENOBUFS
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if there are no slots available in the buf_ring and
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.Dv 0
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on success.
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.Pp
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The
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.Fn drbr_dequeue
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2012-03-29 05:02:12 +00:00
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and
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2012-01-30 21:02:25 +00:00
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.Fn drbr_dequeue_cond
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functions return an mbuf on success and
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.Dv NULL
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if the buf_ring is empty.
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.Sh HISTORY
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These functions were introduced in
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.Fx 8.0 .
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