Vault 2015

Jun He (UW-Madison) will present Chopper, a tool that efficiently explores the vast input space of file system policies to find behaviors that lead to high-tail latencies. Jun He will focus specifically on block allocation, as complex allocation policies can lead to surprising and costly performance problems. The approach utilizes sophisticated statistical methodologies to explore the search space efficiently while still ensuring excellent coverage of system responses. Chopper has been applied to study the over all behavior of two file systems, and to study Linux ext4 in depth. Chopper is able to identify four internal design issues in ext4 which form a large tail in its performance distribution. By removing the underlying problems in the code, consistent and satisfactory file layouts are achieved.