[PATCH man-pages] packet.7: improve PACKET_QDISC_BYPASS description

[PATCH man-pages] packet.7: improve PACKET_QDISC_BYPASS description

[Daniel Borkmann]

Improve the description resp. provide some more details.

Signed-off-by: Daniel Borkmann <dborkman-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
---
 man7/packet.7 | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/man7/packet.7 b/man7/packet.7
index 1d3f222..7a2ce1e 100644
--- a/man7/packet.7
+++ b/man7/packet.7
@@ -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.
-- 
1.7.11.7

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Re: [PATCH man-pages] packet.7: improve PACKET_QDISC_BYPASS description

[Michael Kerrisk (man-pages)]

On 02/14/2014 11:34 AM, Daniel Borkmann wrote:
> Improve the description resp. provide some more details.
> 
> Signed-off-by: Daniel Borkmann <dborkman-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
> ---
>  man7/packet.7 | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/man7/packet.7 b/man7/packet.7
> index 1d3f222..7a2ce1e 100644
> --- a/man7/packet.7
> +++ b/man7/packet.7
> @@ -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.
> 

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

-- 
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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Re: [PATCH man-pages] packet.7: improve PACKET_QDISC_BYPASS description

[Daniel Borkmann]

On 02/23/2014 08:35 AM, Michael Kerrisk (man-pages) wrote:
...
> Okay?

Yes, thanks Michael!
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