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

CHAPTER 4. EXPERIMENTAL SETUP 31
4.5 System Environment Configuration
To create a simple, controlled test environment, the experiments were mainly executed in the file system
address space (server-level) and no other major servers were running at the time. For instance, the NFS
server, RAM file system, toy file system, device file system, pipe server, and pty server were all disabled. For
each microbenchmark, the computer system was booted, HFS was initialized, and the appropriate benchmark
was executed. Running at the server-level allowed the file system to be stressed without invoking the VFS
and FCM components of the operating system.
For the few user-level experiments, the services of the pipe server and pty server were required and
enabled. When running the experiments at user-level, the K42 file cache manager cached all file data blocks
and all requests for file data blocks were satisfied from the file cache from the second run of the experiment
onward 2 . Also, the VFS component cached portions of file meta-data such as file attributes. Therefore, the
user-level experiments stressed the FCM and VFS components of the operating system.
The version of K42 used did not have FCM page eviction (i.e. page-out) enabled because of problems in
the implementation at the time the experiments were run. The workloads used in the experiments are not
affected by this missing feature.
4.6 Measurements Taken and Graph Interpretation
We measured scalability for 1, 2, 4, 8, and 12 processor configurations. For the microbenchmarks, each
experiment was repeated 10 times under each processor configuration. Each repetition consisted of an initial
warm up run, followed by a subsequent identical measured run. For each thread, we measured the number
of cycles taken to complete its task. For a measured run of the experiment on a uniprocessor, we obtain one
number from the single thread of execution. On a dual processor, we obtain two numbers, one from each of
the two threads of execution. On a four processor computer, we obtain four numbers from each of the four
threads of execution.
After 10 measured runs, we have 10, 20, 40, 80, and 120 values for processor configurations of 1, 2, 4, 8,
and 12, respectively. We plot the average of these corresponding numbers to obtain a curve. We also note
the minimum and maximum cycle counts for each configuration.
The y-axis indicates the average number of cycles required by each thread while the x-axis indicates the
number of processors. The ideal scalability graph would be a flat, perfectly horizontal curve, indicating that
thread execution time is independent of system size.
Due to time constraints and speed limitations of the SimOS simulator, the macrobenchmark experiments
were repeated only twice.
2 Main memory is sized adequately to allow all file data to be cached.