- Update and expand description of node operation.
- Cut section IMPLELEMENTATION NOTES. It doesn't apply to modern FreeBSD. Sponsored by: Rambler
This commit is contained in:
Gleb Smirnoff
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commit
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@ -32,12 +32,12 @@
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.\" Author: Dave Chapeskie <dchapeskie@sandvine.com>
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.\" $FreeBSD$
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.\"
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.Dd November 1, 2002
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.Dd April 5, 2005
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.Dt NG_SOURCE 4
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.Os
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.Sh NAME
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.Nm ng_source
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.Nd netgraph discard node type
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.Nd netgraph node for traffic generation
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.Sh SYNOPSIS
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.In sys/types.h
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.In netgraph/ng_source.h
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@ -47,51 +47,61 @@ The
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node acts as a source of packets according to the parameters set up
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using control messages and input packets.
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The
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.Dv output
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hook must also be connected to a node that responds to the
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.Dv NGM_ETHER_COOKIE Ns / Ns
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.Dv NGM_ETHER_GET_IFINDEX
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message (e.g., an
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.Xr ng_ether 4
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node).
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This type is used for testing and debugging.
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.Pp
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The operation of the node is as follows:
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.Bl -bullet
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.It
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Packets received on the
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.Dv input
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hook are queued internally.
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.It
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On reception of a
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.Dv NGM_SOURCE_START
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message the node starts sending
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the queued packets out the
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.Dv output
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hook on every clock tick as fast
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as the connect interface will take them.
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.It
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While active, on every clock tick the node checks the available space
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in the
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.Va ifqueue
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of the interface connected to the output hook and sends
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that many packets out its
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.Dv output
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hook.
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.It
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Once the number of packets indicated in the start message have been
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sent, or on reception of a stop message, the node stops sending data.
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.El
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.Nm
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node type is used primarily for testing and benchmarking.
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.Sh HOOKS
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The
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.Nm source
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node has two hooks:
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.Dv input
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.Va input
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and
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.Dv output .
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.Va output .
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The
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.Dv output
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.Va output
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hook must remain connected, its disconnection will shutdown the node.
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.Sh OPERATION
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The operation of the node is as follows.
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Packets received on the
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.Va input
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hook are queued internally.
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When
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.Va output
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hook is connected,
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.Nm
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node assumes that its neighbour node is of
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.Xr ng_ether
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node type.
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The neighbor is queried for its interface name.
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.Nm
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node then uses queue of the interface for its evil purposes.
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.Nm
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node also disables
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.Va autosrc
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option on neighbour
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.Xr ng_ether
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node.
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If interface name can't be obtained automatically, it should
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be configured explicitly with help of
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.Dv NGM_SOURCE_SETIFACE
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control message, and
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.Va autosrc
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should be turned off on
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.Xr ng_ether
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node manually.
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.Pp
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Once interface is configured, upon receival of
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.Dv NGM_SOURCE_START
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control message the node starts sending
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the previously queued packets out the
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.Va output
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hook on every clock tick as fast
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as the connected interface will take them.
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While active, on every clock tick the node checks the available space
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in the interface queue and sends that many packets out its
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.Va output
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hook.
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Once the number of packets indicated in the start message have been
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sent, or upon reception of a stop message, the node stops sending data.
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.Sh CONTROL MESSAGES
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This node type supports the generic control messages as well as the following,
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which must be sent with the
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@ -141,109 +151,29 @@ As
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.Ic getstats
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but clears the statistics at the same time.
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.It Dv NGM_SOURCE_START Pq Ic start
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.Bl -bullet
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.It
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Takes a single
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.Vt u_int64_t
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This message requires a single
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.Vt uint64_t
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parameter which is the number of packets to
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send before stopping.
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.It
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Starts sending the queued packets out the output hook.
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.It
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The output hook must be connected or
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.Er EINVAL
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is returned.
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.It
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The node connected to the output hook must respond to
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.Dv NGM_ETHER_GET_IFINDEX
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which is used to get the
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.Va ifqueue
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of the attached interface.
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.It
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.Dv NGM_ETHER_SET_AUTOSRC
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is sent to the node connected to the
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.Dv output
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hook
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to turn off automatic Ethernet source address overwriting (any errors
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from this message are ignored).
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.El
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Node starts sending the queued packets out the output hook.
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The output hook must be connected and node must have
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interface configured.
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.It Dv NGM_SOURCE_STOP Pq Ic stop
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Stops the node if it is active.
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.It Dv NGM_SOURCE_CLR_DATA Pq Ic clrdata
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Clears the packets queued from the
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.Dv input
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hook.
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.It Dv NGM_SOURCE_SETIFACE Pq Ic setiface
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This message requires a string argument - name of the interface
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to be configured.
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.El
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.Sh SHUTDOWN
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This node shuts down upon receipt of a
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.Dv NGM_SHUTDOWN
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control message, or when the
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.Dv output
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control message, when all hooks has been disconnected, or when the
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.Va output
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hook has been disconnected.
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.Sh IMPLEMENTATION NOTES
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.No ( Fx 4.4
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version)
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.Pp
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The use of
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.Xr splimp 9
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around the
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.Dv NG_SEND_DATA
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loop is important.
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Without it,
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the time taken by a single invocation of
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.Fn ng_source_intr
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becomes too
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large and the packet rate drops.
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Probably due to the NIC starting to
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send the packets right away.
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.Pp
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Copying all the packets in one loop and sending them in another inside
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of
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.Fn ng_source_send
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is done to limit how long we are at
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.Xr splimp 9
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and gave
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minor packet rate increases (~5% at 256 byte packets).
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However note
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that if there are errors in the send loop, the remaining copied packets
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are simply freed and discarded; thus we skip those packets, and ordering
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of the input queue to the output is not maintained.
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.Pp
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Calling
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.Xr timeout 9
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at the end of
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.Fn ng_source_intr
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instead of near the
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beginning is done to help avoid CPU starvation if
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.Fn ng_source_intr
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takes a long time to run.
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.Pp
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The use of
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.Xr splnet 9
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may be sub-optimal.
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It is used for synchronization
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within the node (e.g., data received on the
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.Dv input
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hook while
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.Fn ng_source_send
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is active) but we do not want to hold it too long and risk
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starving the NIC.
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.Pp
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For clarity and simplicity, debugging messages and instrumentation code
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has been removed.
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On i386 one can include
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.In machine/cpufunc.h
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to have access to the
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.Fn rdtsc
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function to read the instruction counter at the
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start and end of
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.Fn ng_source_intr .
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Also useful is the packet count returned by
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.Fn ng_source_send .
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Do not try to report such things from within
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.Fn ng_source_intr ,
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instead include the values in
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.Va sc->stats .
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.Sh EXAMPLES
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Attach the node to an
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.Xr ng_ether 4
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