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packet.7: improve PACKET_QDISC_BYPASS description

PATCH In review Daniel Borkmann 2 participants 3 messages Feb 14, 2014 – Feb 23, 2014 4 messages not in the archive Man-pages: manual pages for Linux -- Sections 2, 3, 4, 5, and 7

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Daniel Borkmann

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#2 lore raw

PATCH 1/1 packet.7: improve PACKET_QDISC_BYPASS description

Improve the description resp. provide some more details.

Signed-off-by Daniel Borkmann <[email protected]>
---
 man7/packet.7 | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)
man7/packet.7 +8 -3
index 1d3f222..7a2ce1e 100644
@@ -431,9 +431,14 @@ integer option before creating the ring.
 .BR PACKET_QDISC_BYPASS " (since Linux 3.14)"
 .\" commit d346a3fae3ff1d99f5d0c819bf86edf9094a26a1
 By default, packets sent through packet sockets pass through the kernel's
-qdisc (traffic control) layer.
-This can be bypassed by setting this integer option to 1;
-this is useful for usage scenarios similar to pktgen.
+qdisc (traffic control) layer, which is fine for the vast majority of use
+cases.
+For traffic generator appliances using packet socket that intend to flood
+the network with brute force i.e., to test devices under load in a similar
+fashion to pktgen, this layer can be bypassed by setting this integer option
+to 1. Side-effects are that packet buffering in qdisc layer is avoided
+which will lead to increased drops when net device transmit queues are busy;
+therefore, use at your own risk.
 .SS Ioctls
 .B SIOCGSTAMP
 can be used to receive the timestamp of the last received packet.
Signature · 6 lines
1.7.11.7

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A message that is not in the archive (sent off-list or not yet received): e28f3b491ae1d2e4538ef6b84871eb773185f089.1392373992.git.dborkman-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org

#4 lore raw
Quoted 20 lines · Daniel Borkmann

Improve the description resp. provide some more details.

Signed-off-by Daniel Borkmann <[email protected]>
---
 man7/packet.7 | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)
man7/packet.7 +1 -3
index 1d3f222..7a2ce1e 100644
@@ -431,9 +431,14 @@ integer option before creating the ring.
 .BR PACKET_QDISC_BYPASS " (since Linux 3.14)"
 .\" commit d346a3fae3ff1d99f5d0c819bf86edf9094a26a1
 By default, packets sent through packet sockets pass through the kernel's
-qdisc (traffic control) layer.
-This can be bypassed by setting this integer option to 1;
-this is useful for usage scenarios similar to pktgen.
+qdisc (traffic control) layer, which is fine for the vast majority of use

man7/packet.7 integer option before creating the ring. · line 444

Quoted 10 lines
man7/packet.7 +7 -0
+cases.
+For traffic generator appliances using packet socket that intend to flood
+the network with brute force i.e., to test devices under load in a similar
+fashion to pktgen, this layer can be bypassed by setting this integer option
+to 1. Side-effects are that packet buffering in qdisc layer is avoided
+which will lead to increased drops when net device transmit queues are busy;
+therefore, use at your own risk.
 .SS Ioctls
 .B SIOCGSTAMP
 can be used to receive the timestamp of the last received packet.

Thanks, Daniel. I applied, and then tweaked the text a little:

PACKET_QDISC_BYPASS (since Linux 3.14)
By default, packets sent through packet sockets pass through the kernel's qdisc (traffic control) layer, which is fine for the vast majority of use cases. For traffic generator appliances using packet sockets that intend to brute-force flood the network—for example, to test devices under load in a similar fashion to pktgen—this layer can be bypassed by setting this integer option to 1. A side-effects is that packet buffering in the qdisc layer is avoided, which will lead to increased drops when network device transmit queues are busy; therefore, use at your own risk.
Okay?

Thanks,

Michael

Signature · 7 lines
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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