packet: introduce PACKET_QDISC_BYPASS socket option

[cascardo/linux.git] / Documentation / networking / packet_mmap.txt

diff --git a/Documentation/networking/packet_mmap.txt b/Documentation/networking/packet_mmap.txt
index 8e48e3b..4288ffa 100644 (file)
--- a/Documentation/networking/packet_mmap.txt
+++ b/Documentation/networking/packet_mmap.txt
@@ -952,6 +952,27 @@ int main(int argc, char **argp)
        return 0;
 }
 
+-------------------------------------------------------------------------------
++ PACKET_QDISC_BYPASS
+-------------------------------------------------------------------------------
+
+If there is a requirement to load the network with many packets in a similar
+fashion as pktgen does, you might set the following option after socket
+creation:
+
+    int one = 1;
+    setsockopt(fd, SOL_PACKET, PACKET_QDISC_BYPASS, &one, sizeof(one));
+
+This has the side-effect, that packets sent through PF_PACKET will bypass the
+kernel's qdisc layer and are forcedly pushed to the driver directly. Meaning,
+packet are not buffered, tc disciplines are ignored, increased loss can occur
+and such packets are also not visible to other PF_PACKET sockets anymore. So,
+you have been warned; generally, this can be useful for stress testing various
+components of a system.
+
+On default, PACKET_QDISC_BYPASS is disabled and needs to be explicitly enabled
+on PF_PACKET sockets.
+
 -------------------------------------------------------------------------------
 + PACKET_TIMESTAMP
 -------------------------------------------------------------------------------