103
of nodes increases. The UCB trace shows more than 100% throughput improvement
compared to the base model as the number of nodes reaches seven. Finally, as expected,
the PSU trace does not have any benefit from the NIC caching scheme because the
extended cache space does not help in increasing the cache hit ratio as seen in Figure 5.9.
5.7.2
The Inclusive NIC Caching Scheme
The inclusive caching scheme aims at caching the N most popular data items in
the main memory cache. Thus, the NIC cache is a subset of the main memory cache of a
Web server. The rationale of the inclusive scheme is that since these files are frequently
requested by the remote servers, making them available in the NIC memory reduces the
intra node traffic and the DMA transfer time, compared to reading data from the remote
main memory.
Figure 5.11 shows the throughput of the three traces as a function of the number
of nodes in a cluster when the inclusive scheme is used. Interestingly, these results are
very compared to those of Figure 5.10. The CSE trace shows about 10% throughput
improvement compared to the exclusive scheme at a single node, and yields 14%, 23
% and 25.8 % throughput improvements with 2, 5 and 8 nodes compared to the orig 
inal system, respectively. This is because the CSE trace has many large size files and
the intra cluster communication mechanism (i.e., PCI bus) becomes the bottleneck for
heavy traffic. Since the inclusive scheme reduces the PCI bus traffic and DMA latency
significantly, it is particularly beneficial for the trace with large size files.
For the UCB trace, while the exclusive scheme shows the maximum throughput
improvement, the inclusive scheme does not yield any performance improvement. This is












  

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