Effect of timer interrupt interval on file system synchronization overhead

摘要

File system metadata is indispensable in both describing the data and maintaining the file system. Despite the importance of metadata in the file system, the overhead of maintaining the metadata cannot be taken lightly. It is because the metadata also have to be persisted on the storage device and it consumes IO bandwidth as well as creates journaling overhead. In this paper, we find that the random write with synchronous performance of a storage is significantly affected by not only the hardware performance but also timer interrupt interval of the kernel. Extending the timer interrupt interval allows reducing the write volume and increasing the random write followed by fsync() performance of EXT4 file system. We propose intermittent mtime timestamp update on Coarse grain mtime interval instead of Fine grain mtime interval. The experiment results with mtime update interval of 1 second show that the total write volume is decreased by 75% and 28%, respectively compared to total write volume of 1 ms and 10 ms mtime interval, and the throughput increased 3.1× and 1.2× compared to 1 ms and 10 ms mtime interval. Coarse grain mtime update is resolve to the journaling overhead issues while still logging mtime timestamp.