pktgen: document ability to add same device to several threads

The pktgen.txt documentation still claimed that adding same device to
multiple threads were not supported, but it have been since 2008 via
commit e6fce5b9 ("pktgen: multiqueue etc.").

Document this and describe the naming scheme dev@X, as the procfile name
still need to be unique.

Fixes: e6fce5b9 ("pktgen: multiqueue etc.")
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Acked-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/pktgen.txt

@@ -50,16 +50,33 @@ For ixgbe use e.g. "30" resulting in approx 33K interrupts/sec (1/30*10^6):
  # ethtool -C ethX rx-usecs 30
 
 
-Viewing threads
-===============
-/proc/net/pktgen/kpktgend_0
-Running:
-Stopped: eth1
-Result: OK: add_device=eth1
+Kernel threads
+==============
+Pktgen creates a thread for each CPU with affinity to that CPU.
+Which is controlled through procfile /proc/net/pktgen/kpktgend_X.
+
+Example: /proc/net/pktgen/kpktgend_0
+
+ Running:
+ Stopped: eth4@0
+ Result: OK: add_device=eth4@0
+
+Most important are the devices assigned to the thread.
 
-Most important are the devices assigned to the thread.  Note that a
-device can only belong to one thread.
+The two basic thread commands are:
+ * add_device DEVICE@NAME -- adds a single device
+ * rem_device_all         -- remove all associated devices
 
+When adding a device to a thread, a corrosponding procfile is created
+which is used for configuring this device. Thus, device names need to
+be unique.
+
+To support adding the same device to multiple threads, which is useful
+with multi queue NICs, a the device naming scheme is extended with "@":
+ device@something
+
+The part after "@" can be anything, but it is custom to use the thread
+number.
 
 Viewing devices
 ===============
@@ -68,29 +85,32 @@ The Params section holds configured information.  The Current section
 holds running statistics.  The Result is printed after a run or after
 interruption.  Example:
 
-/proc/net/pktgen/eth1
+/proc/net/pktgen/eth4@0
 
-Params: count 10000000  min_pkt_size: 60  max_pkt_size: 60
-     frags: 0  delay: 0  clone_skb: 1000000  ifname: eth1
+ Params: count 100000  min_pkt_size: 60  max_pkt_size: 60
+     frags: 0  delay: 0  clone_skb: 64  ifname: eth4@0
      flows: 0 flowlen: 0
-     dst_min: 10.10.11.2  dst_max: 
+     queue_map_min: 0  queue_map_max: 0
+     dst_min: 192.168.81.2  dst_max:
      src_min:   src_max:
-     src_mac: 00:00:00:00:00:00  dst_mac: 00:04:23:AC:FD:82
-     udp_src_min: 9  udp_src_max: 9  udp_dst_min: 9  udp_dst_max: 9
+     src_mac: 90:e2:ba:0a:56:b4 dst_mac: 00:1b:21:3c:9d:f8
+     udp_src_min: 9  udp_src_max: 109  udp_dst_min: 9  udp_dst_max: 9
      src_mac_count: 0  dst_mac_count: 0
-     Flags: 
-Current:
-     pkts-sofar: 10000000  errors: 39664
-     started: 1103053986245187us  stopped: 1103053999346329us idle: 880401us
-     seq_num: 10000011  cur_dst_mac_offset: 0  cur_src_mac_offset: 0
-     cur_saddr: 0x10a0a0a  cur_daddr: 0x20b0a0a
-     cur_udp_dst: 9  cur_udp_src: 9
+     Flags: UDPSRC_RND  NO_TIMESTAMP  QUEUE_MAP_CPU
+ Current:
+     pkts-sofar: 100000  errors: 0
+     started: 623913381008us  stopped: 623913396439us idle: 25us
+     seq_num: 100001  cur_dst_mac_offset: 0  cur_src_mac_offset: 0
+     cur_saddr: 192.168.8.3  cur_daddr: 192.168.81.2
+     cur_udp_dst: 9  cur_udp_src: 42
+     cur_queue_map: 0
      flows: 0
-Result: OK: 13101142(c12220741+d880401) usec, 10000000 (60byte,0frags)
-  763292pps 390Mb/sec (390805504bps) errors: 39664
+ Result: OK: 15430(c15405+d25) usec, 100000 (60byte,0frags)
+  6480562pps 3110Mb/sec (3110669760bps) errors: 0
+
 
-Configuring threads and devices
-================================
+Configuring devices
+===================
 This is done via the /proc interface, and most easily done via pgset
 as defined in the sample scripts.
 
@@ -221,6 +241,9 @@ Note that when adding devices to a specific CPU it is a good idea to
 also assign /proc/irq/XX/smp_affinity so that the TX interrupts are bound
 to the same CPU.  This reduces cache bouncing when freeing skbs.
 
+Plus using the device flag QUEUE_MAP_CPU, which maps the SKBs TX queue
+to the running threads CPU (directly from smp_processor_id()).
+
 Enable IPsec
 ============
 Default IPsec transformation with ESP encapsulation plus transport mode