Throughput vs. Data Size: Transmit

The next series of experiments investigates the effect of the per-write() data size on the overall throughput. The data was gathered with the same nettest program and 100 MByte copies, but the amount of data copied per write() was varied from 512 to 65536 bytes by powers of two. 30 runs were taken and averaged at each data size with both the optimized and 2.0 versions. Figure 6 shows the sustained transmit throughput from the various machine configurations and optimization levels. As expected, the native machines (both PC-733 and PC-350 achieve identical throughput) saturate the 100 Mbit link. VM/PC-733 becomes CPU bound well before saturating the network link. With the optimizations however, VM/PC-733 matches native throughput. Although VM/PC-350 remains CPU bound with the optimizations, its sustained throughput doubles and matches the performance of the unoptimized VM/PC-733. The two VM/PC-350 curves are consistent in shape with their PC-733 counterparts.