IEEE Computer Society and GBC/ACM

online 7:00 PM, Thursday, 20 October 2022

KUtrace: Where does every nanosecond go in complex latency-sensitive software?

Richard L. Sites, ex-DEC

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Abstract:

Observation tools for understanding occasionally-slow performance in large-scale distributed transaction systems are not keeping up with the complexity of the environment. The same is true for large database systems, real-time control systems, and operating systems themselves.

KUtrace is a low-overhead tracing tool that reveals the true execution and non-execution (waiting) dynamics of such software, running in situ with live traffic. It is based on small FreeBSD or Linux kernel patches recording and timestamping every transition between kernel- and user-mode execution across all CPUs. The resulting postprocessed display shows exactly what each action/response is doing every nanosecond, and hence shows the root cause(s) for unpredictably-slow responses, including interference between programs. Tracing overhead is well under 1%.

Even without a similar observation tool for GPU execution, CPU-only tracing shows GPU delays and CPU-GPU interaction delays. The net result is deep insight into the dynamics of complex software, leading to often-simple changes to improve performance.

Bio:

Dr. Richard L. Sites wrote his first computer program in 1959 and has spent most of his career at the boundary between hardware and software, with a particular interest in CPU/ software performance. His past work includes VAX microcode, DEC Alpha co-architect, and inventing the performance counters found in nearly all processors today. He has done low-overhead microcode and software tracing at DEC, Adobe, Google, and Tesla. Dr. Sites earned his PhD at Stanford in 1974; he holds 66 patents and is a member of the National Academy of Engineering. His book Understanding Software Dynamics was published by Addison-Wesley in late 2021.

This joint meeting of the Boston Chapter of the IEEE Computer Society and GBC/ACM will be online only due to the COVID-19 lockdown.

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