# On Linux Vdso and Clockgettime

DevFeed: [On Linux Vdso and Clockgettime](<https://devfeed.tech/articles/on-linux-vdso-and-clockgettime-36503.md>)

Original publisher: [Read original article](<https://berthub.eu/articles/posts/on-linux-vdso-and-clockgettime/>)

Published: 2017-03-24T18:22:18Z

Content type: article

Language: en

Sources: [Bert Hubert's writings](<https://devfeed.tech/sources/bert-hubert-s-writings.md>)

Topics: [Linux](<https://devfeed.tech/topics/linux.md>), [benchmarking](<https://devfeed.tech/topics/benchmarking.md>), [Kernel](<https://devfeed.tech/topics/kernel.md>), [C](<https://devfeed.tech/topics/c.md>), [Code](<https://devfeed.tech/topics/code.md>)

Tags: [benchmarking](<https://devfeed.tech/tags/benchmarking.md>), [c](<https://devfeed.tech/tags/c.md>), [code](<https://devfeed.tech/tags/code.md>), [kernel](<https://devfeed.tech/tags/kernel.md>), [linux](<https://devfeed.tech/tags/linux.md>), [programming](<https://devfeed.tech/tags/programming.md>)

## AI overview

The article investigates why Linux clock_gettime calls can sometimes be slow despite clock_gettime being available in the kernel-provided vDSO. It describes discovering millions of clock_gettime system calls during dnsdist benchmarking and examining the vDSO and glibc code to understand why the vDSO implementation was not used.

## Source excerpt

On Linux vDSO and clock_gettime sometimes being slow Like the previous post on this somewhat dormant blog, I want to share an oddity I discovered that no search engine could really find for me - even though once I found what the problem was, it turns out I was by no means the first person to discover this. Some system calls that are used extremely frequently in Linux can be speeded up by a mechanism called vDSO: a virtual dynamically linked shared object.