hoiop.blogg.se - Transmit buffers

#TRANSMIT BUFFERS FULL#

And don’t forget to check errpt as many problems show up there. You can check what it’s set to using “lsattr –EL ent?”.Īdditionally you should look for receive or transmit errors, DMA overruns and DMA underruns. Look for “S/W transmit queue overflow”-if you see these or “packets dropped due to memory allocation failure”, you must increase the adapter transmit queue. nmon provides great statistics the –O flag now provides network statistics on the SEA, which is very useful. Several commands are useful when looking at network performance. Setting tcp_nodelay to 1 is a dynamic change and a tradeoff between more network traffic versus better response time.

#TRANSMIT BUFFERS FULL#

Clearly this causes delays in sending further packets until either the acknowledgement is received or TCP can bundle up more data into a full segment. The nagle algorithm means that a TCP connection can only have one outstanding acknowledgement for a small segment. Normally, TCP implements delayed acknowledgements, where it tries to piggyback a TCP acknowledgement onto a response packet this delay is usually up to 200ms. Setting this to 1, instead of the default 0, causes TCP to send each packet out immediately for each application send or write.

tcp_nodelay is often used in a database environment.

udp_recvspace is typically set much higher than udp_sendspace as multiple datagrams can arrive at the same time and multiple applications tend to share sockets listening for UDP datagrams. You can tell if packets are being dropped by issuing the “netstat –p udp” command and looking for socket buffer overflows. Once the udp_recvspace limit is reached, incoming packets are discarded.

udp_sendspace is used for UDP datagram buffering for send, and udp_recvspace controls the amount of space used for queuing incoming data on the UDP socket.

The default is rfc1323=0 (off) so it’s important to set this tunable if you plan to set TCP send and receive higher than 65536 (which I’m recommending). This must be set to 1 on both sides of the connection otherwise the effective value of the tcp_recvspace tunable will be 65536, even though you may have set it to 262144.

rfc1323 is also known as the TCP window scaling option.

For high-speed adapters, it should be at least twice the size of tcp_recvspace. The recommendation for performance is that it should be set to at least the same size as tcp_recvspace.

tcp_sendspace specifies how much data the sending application can buffer in the kernel before the application is blocked on a send call.

tcp_recvspace specifies how many bytes of data the receiving system can buffer in the kernel on the receiving sockets queue.For Gbit adapters: chdev -l ent0 -a txdesc_que_sz=1024 -a tx_que_sz=16384 -Pīoth changes would be activated after a reboot (the –P sets that). The adapter can be set as follows: chdev -l en0 -a tcp_recvspace=262144 –a tcp_sendspace=262144 –a rfc1323=1 –Pĭepending on the load (I do this for the base adapters on my SEAs but also on busy systems), you may want to increase the adapter transmit queues. If the TCP send, receive and/or rfc1323 is set, they should be changed to match the above, unless the settings on the adapter are larger. You’ll see something like the following: en0: flags=1e080863,480 Check by running the “ifconfig –a” command. These defaults only come into play if nothing has been set on the actual adapter, which is the case for certain (more recent) AIX releases. Typically, you receive about 10 times as many UDP packets as you send, hence the difference in the values. Since DNS and other protocols use UDP, it’s important to increase those values. It’s common to see the TCP values changed but many leave UDP at the defaults. This example sets TCP send and receive buffers to 256K, UDP send to 64K and UDP receive to 640K. The first set is done using the no command. Given that most customers are running GB or 10 GB networks, the first step to improving network performance is to set some basic tunables. By default, the network tunables on an AIX system aren’t set optimally for anything above a 100 MB network.