Performance of vanilla Linux based readout system for B-factory upgrade

KEKB B-factory is now aiming for an upgrade to a luminosity of a few times 10³⁵cm^-2s^-1, where the trigger rate will increase up to 30 kHZ. This is beyond the capability of the current data acquisition system, and therefore we introduce a new system based on a common 9U VME mother board, consisting of a frontend and a processor part. For the processor part. We choose a commercially available PMC CPU module with a PC-based architecture and an Intel CPU, and a vanilla Linux operating system on which the Belle-standard analysis software framework is utilized for the data processing. Since realtime logics are implemented in the on-board FPGA, we do not require any realtime Linux extensions. We have measured the performance of such a system, including the CPU consumption, process interruption rate, and total data transfer rate. We demonstrate that Linux with no realtime extension really can cope with the upgrade plan of Belle and prove advantages of this approach through these measurements.