DJ Delorie

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The Non-complexity of /etc/nsswitch.conf

The Non-complexity of /etc/nsswitch.conf

In most glibc-based operating systems, there’s a file /etc/nsswitch.conf that most people ignore, few people understand, but all people generally rely on. This file determines where the system finds things like host names, passwords, and protocol numbers. Does your company use LDAP? NIS? Plain files? The nsswitch file (it stands for “name services switch”) tells the system what service to use for each type of name lookup.

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Why you should care about RISC-V

Why you should care about RISC-V

If you haven’t heard about the RISC-V (pronounced “risk five”) processor, it’s an open-source (open-hardware, open-design) processor core created by the University of Berkeley. It exists in 32-bit, 64-bit, and 128-bit variants, although only 32- and 64-bit designs exist in practice. The news is full of stories about major hardware manufacturers (Western Digital, NVidia) looking at or choosing RISC-V cores for their product.

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Practical micro-benchmarking with ‘ltrace’ and ‘sched’

Practical micro-benchmarking with ‘ltrace’ and ‘sched’

Recently I was asked to look into an issue related to QEMU’s I/O subsystem performance – specifically, I was looking for differences in performance between glibc’s malloc and other malloc implementations’. After a good deal of benchmarking I was unable to see a clear difference between our malloc (glibc) and others, not because the implementations were similar, but because there was too much noise in the system; the benchmarks were being polluted by other things, not just in QEMU, but elsewhere in the operating system. I really just wanted to see how much time malloc was using, but it was a small signal in a large noisy system.

To get to the results I needed, I had to isolate malloc’s activity so I could measure it more accurately. In this blog, I’ll document how I extracted the malloc workload, and how to isolate that workload from other system activity so it can be measured more effectively.

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