On Wed, 2010-06-23 at 15:33 -0500, Ron Foster at Baldor-IS wrote: > I know that if I am using hipersockets to communicate from a zLinux > guest under zVM to a zOS LPAR, that I might be able to see improved > performance if I increased the buffer_count from it's default of 16 to > something higher. > > I have seen information indicating if I have a directly attached OSA > adapter to communicate with other systems, that I might be able to > improve performance by increasing buffer_count. > > But what about a zLinux guest, is there likely to be any performance > improvement if I increase the buffer_count for a device attached to a > VSWITCH? > Ron,
buffer_count determines the number of input buffers that the qeth driver shares with the (real or virtual) device. Every buffer is either controlled by Linux (when processing inbound data) or by the device (when providing inbound data). Initially Linux hands over control to the device for all available input buffers. The device fills (some of) them and notifies Linux. Now Linux controls these buffers, processes them, and returns control back to the device. The device can provide inbound data only, if it controls at least 1 input buffer. That means, increasing the buffer_count increases the probability that the device controls input buffers to provide inbound data. The maximum number of input buffers is 128. The only reason qeth chooses a default of 16 as buffer_count are memory-constrained systems. One buffer uses 64K of kernel memory. If your system is not memory-constrained and if the expected burst workload for your network connection is high, it makes always sense to increase buffer_count of a qeth device to 128. This applies to a VSWITCH-attached device as well. Regards, Ursula Braun, IBM Germany, Linux on System z development ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390 ---------------------------------------------------------------------- For more information on Linux on System z, visit http://wiki.linuxvm.org/
