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

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CHAPTER 4. EXPERIMENTAL SETUP 33 memory results is shown in Figure 4.3. These results demonstrate that the perfect memory model eliminated memory bank access time, bus access time, and cache coherency overhead. 4.7.2 Memory System Saturation The SimOS memory system parameters are given in Table 4.1. For instance: 177 MB/s bus bandwidth, 1 memory bank, and 2100 ns memory access time are critical memory parameters. However, these parameters alone do not describe memory system behavior under increasing contention. We ran a simple experiment to depict the characteristics and limitations of the memory system. File system scalability is limited to the maximal throughput of these hardware components. In the experiment, each processor executes a thread that sequentially traverses a separate, independent 2 MB array, reading and modifying each array element. The nature of the modification is a simple increment of the current value in the array element. Each element is 1 byte in size. The array is allocated local to each processor, using K42’s memory allocation routines. The allocation performs padding at the array boundaries to prevent false sharing of cache lines. The 2 MB array size ensured the data set would not fit in the 1 MB secondary cache so that read and write accesses to main memory were necessary. The goal of the experiment was to saturate the bus or the sole memory bank with memory traffic from the array accesses to determine the maximum load that can be placed on the system. Figure 4.4 shows that performance was satisfactory for up to 4 processors but degraded drastically beyond this point. Under continuous, intense pressure, the bus or memory bank could adequately service a maximum of 4 processors. In practice, this worst-case scenario should rarely occur since the processor caches should reduce the amount of memory bus traffic.
Chapter 5 Microbenchmarks – Read Operation 5.1 Purpose One of the basic tasks of a file system is to act as a translation layer between the operating system and the disk device driver. The file system receives a logical file block number from the operating system, translates it into a physical disk block number, and asks the disk device driver to operate on the physical disk block. The first microbenchmark measures the scalability of this fundamental operation. 5.2 Experimental Setup The first benchmark attempts to determine the maximum concurrency and throughput of the file system under the following configuration. In this experiment, a worker thread is allocated to each processor. In parallel, each thread sequentially reads a separate 12,845,056 byte extent-based file located on separate disks that it accesses exclusively. Figure 3.2 on page 17 shows an example of the block index of an extent- based file. The particular file size was chosen so that the block index occupied exactly 1 meta-data cache entry. A 12,845,056 byte file contains 3136 blocks. Each thread performs the following general operations 3136 times. (1) Obtain the file status on the target file. (2) Perform a block read operation on the target block. (3) Update the file status information. Steps 1 and 3 are required to reflect the time-stamping activity of the file system during a read operation. An ideal file system would scale perfectly under this workload since each thread is operating on its own processor and disk. A conceptual view of the experimental setup is shown in Figure 5.1. 128 MB of RAM was provided. Optimizations and variations are explored in Section 5.4 and Section 5.5. 34
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Bibliography [1] Gene M. Amdahl. Va
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BIBLIOGRAPHY 88 [33] David Kotz, So
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BIBLIOGRAPHY 90 [71] Keith A. Smith
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