Performance Analysis and Optimization of the Hurricane File System ...

CHAPTER 7. MACROBENCHMARK 75
avg # cycles per processor
6e+10
4e+10
2e+10
0e+00
2 4 6 8 10 12
# processors
Unoptimized + logging
Unoptimized
Figure 7.8: Web server – unoptimized
+logging.
avg # cycles per processor
2e+09
1.5e+9
1e+09
5e+08
0e+00
2 4 6 8 10 12
# processors
Optimized 2 + logging
Optimized 2
Figure 7.9: Web server – optimized
2 +logging.
avg # cycles per processor
2e+11
2e+11
1e+11
1e+11
5e+10
0e+00
2 4 6 8 10 12
# processors
Unoptimized +logging +disk
Optimized 2 +logging +disk
Figure 7.10: Web server – +logging
+disk latency.
configuration was not intended to be the final parameters. Cache capacity misses may have been the culprit.
Since the number of hash lists was reduced by a factor of 4, the remaining hash lists may have become 4
times longer. This change would have led to lengthier hash list traversals that accessed more cache entries
more frequently, leading to a greater chance that the hash list elements were not resident in the secondary
physical caches. The resulting additional contention on the memory bus from each processor could have led
to the scalability problems seen in Figure 7.7.
7.3.3 Web Logging
Web logging was implemented to create a slightly more realistic scenario and determine the impact of
contending read and write requests to disks. To simulate efficient Web logging, a new block was written to
a Web log file every 50 requests, emulating the actions of writing a file block to disk once it has been filled
with Web logging data. We used 80 bytes as the typical size of a Web log entry. Each thread appended
to a Web log file located on its designated exclusive disk. We believe this distributed logging technique
would naturally be used in the real world under such a scenario, since using a single global log file located
on a single shared disk would be quite naive and bring an obvious imbalance to the system. Results for the
unoptimized and optimized versions are shown in Figure 7.8 and Figure 7.9. According to these graphs,
Web logging did not affect file system scalability. The microbenchmark results for reading and writing were
accurately reflected under this workload.
7.3.4 Web Logging and 15 ms Disk Latency
In addition to Web logging, a 15 ms disk access latency was introduced to determine the approximate
impact of disk performance on file system scalability. Since disk accesses were made at page granularity,