Mathieu Desnoyers

@DesnoyersMa@discuss.systems
46 Followers
32 Following
26 Posts
I am mostly interested in scalability and real-time behavior of the Linux kernel. A kernel tracer is a key aspect that must be added to Linux in order to improve these aspects. The path towards this involves contribution of new pieces of core infrastructure in the kernel itself so it can support a low-overhead, low-disturbance tracer.
Workhttps://www.efficios.com
CityMontreal
Mathieu Desnoyers4d ago
EfficiOS5d ago

Hi everyone,

The release of LTTng 2.14.0 — codenamed “Orbitales” — is now official !

Four years in the making, this release brings a host of new features,
improvements, and experimental capabilities for you to explore.

Learn what's new since LTTng 2.13 here :

https://lists.lttng.org/pipermail/lttng-dev/2025-June/030990.html

[RELEASE] LTTng 2.14.0 - Orbitales - Linux kernel and user space tracer

Mathieu DesnoyersMay 12

We've published a new blog post explaining the most notable new feature introduced in LTTng 2.14: per-channel buffers. This helps reducing memory use on large many-core systems.

https://lttng.org/blog/2025/05/12/lttng-2.14-memory/

LTTng 2.14 is currently in release candidate phase. Try it out!

Saving memory on many-core hosts with LTTng 2.14 — LTTng

LTTng 2.14 introduces per-channel tracing buffers to reduce memory footprint on large, many-core hosts.

LTTng
Mathieu DesnoyersApr 30
OSU Open Source LabApr 30

We need your help, the future of the OSU Open Source Lab is in jeopardy

https://osuosl.org/blog/osl-future/

Future of OSL in Jeopardy | OSU Open Source Lab

A nonprofit organization working for the advancement of open source technologies.

Mathieu DesnoyersApr 25
EfficiOSApr 24

Hello everyone,

Here is an article from Jonathan Corbet @corbet LWN.net, covering our CEO's appearance at the 2025 Linux Storage, Filesystem, Memory-Management and BPF Summit :

''Per-CPU memory for user space''
https://lwn.net/Articles/1016408/

Per-CPU memory for user space [LWN.net]

Mathieu DesnoyersApr 22
EfficiOSApr 21

Hi !

We're excited to share the first release candidate of LTTng 2.14, codenamed Orbitales!

Put these new features, improvements and experimental capabilities to the test and offer your feedback in the next few weeks before the final version ships :

https://lists.lttng.org/pipermail/lttng-dev/2025-April/030933.html

[RELEASE] LTTng 2.14.0-rc1 - Orbitales - Linux kernel and user space tracer

Mathieu DesnoyersMar 4
EfficiOSMar 3

Hello everyone,

This is a release announcement for the Userspace RCU library version
0.15.0. It has been nearly two years since the 0.14.0 release, so
it is now time to get this out of the door.

The Userspace RCU library implements RCU, atomics, and lock-free
data structures in userspace.

https://lists.lttng.org/pipermail/lttng-dev/2024-December/030893.html

[RELEASE] Userspace RCU 0.15.0

Mathieu DesnoyersMar 4
EfficiOSMar 3

Hi there!

On January 22nd 2025, five years to the day [1] after launching Babeltrace 2.0 “Amqui”, we released Babeltrace 2.1 “Brossard”! 🎉

https://babeltrace.org/docs/release-notes/babeltrace-2.1.0-release-notes.html

Babeltrace 2.1.0 release notes

Mathieu DesnoyersFeb 14
Ondřej Surý (https://isc.org) presented how he leverages the RCU, lock-free queues, and RCU lock-free hash table APIs from https://liburcu.org to improve the performance and response time of the BIND 9 DNS (https://www.isc.org/bind/). He describes the improvements and results in his #fosdem 2025 talk "How to make BIND 9 fast(er)" https://fosdem.org/2025/schedule/event/fosdem-2025-4626-how-to-make-bind-9-fast-er-/
ISC

Open source software information, blogs, events, downloads and support

Mathieu DesnoyersFeb 14
Andy WingoFeb 14

tracepoints: gnarly but worth it

https://wingolog.org/archives/2025/02/14/tracepoints-gnarly-but-worth-it

tracepoints: gnarly but worth it — wingolog

wingolog: article: tracepoints: gnarly but worth it

Mathieu DesnoyersFeb 13

The video recordings of my #fosdem 2025 talks are now published, enjoy!

- "A new cgroup cpu.max.concurrency controller interface file" , FOSDEM 2025 Container devroom, https://fosdem.org/2025/schedule/event/fosdem-2025-6283-a-new-cgroup-cpu-max-concurrency-controller-interface-file/
- "Waste-Free Per-CPU Userspace Memory Allocation", FOSDEM 2025 Kernel devroom, https://fosdem.org/2025/schedule/event/fosdem-2025-6245-waste-free-per-cpu-userspace-memory-allocation/
- "Exa-Tracer: Tracing HPC Supercomputers with LTTng", FOSDEM 2025 HPC, Big Data & Data Science devroom, https://fosdem.org/2025/schedule/event/fosdem-2025-6269-exa-tracer-tracing-hpc-supercomputers-with-lttng/

FOSDEM 2025 - A new cgroup cpu.max.concurrency controller interface file

×
Andy WingoFeb 11

a minor collection in a whippet microbenchmark, 16MB total nursery:
. 366µs total pause time
. 12µs to get the 8 mutators to stop
. every green arrow is one object stolen from a remote chase-lev deque
. a couple workers ran out of work after 42µs and restarted 25µs later when more work was available

traces via https://lttng.org's user-space tracing; output munged by a script so that i could load in perfetto / chrome-tracing's UI

Show threadCF Bolz-TereickFeb 11
@wingo are you happy with the perfetto ui, compared to, say, the chrome thing? Or the Firefox profiler ui?
Show threadAndy WingoFeb 11
@cfbolz i don’t actually see perfecto and the chrome thing as different; or at least i have not used the enough to have an opinion
Show threadAndy WingoFeb 11
@cfbolz no experience with firefox’s, i should look into that
Show threadCF Bolz-TereickFeb 11
@wingo it's more profiling-oriented, maybe? I haven't tried perfetto 😅
Show threadAndy WingoFeb 11
@cfbolz my impression (completely retconned, no knowledge) is that chrome:tracing was a wonderful one-page hack, that was so good they put a team of people on it, it became an android product and now is full of protobufs; but the web ui is the same as it ever was.
Show threadAndy WingoFeb 11
@cfbolz i.e. the ui is now only one part of perfetto, they spend more time getting the data, and the main target is now android rather than the web. but again this is all retconned :)
Show threadCF Bolz-TereickFeb 11
@wingo I quite enjoy the firefox profiler, we generate json for it from python profiles. only thing I'm really missing is a nice call graph view, like kcachegrind has it: https://kcachegrind.github.io/html/Shot3Large.html
KCachegrind

Show threadAndy WingoFeb 11
@cfbolz i dearly love kcachegrind :) honestly that any profiling tool exists at all is a miracle, these things are so ephemeral; you fix your bug and move on, leaving half-finished perf analysis tools to rot
Show threadCF Bolz-TereickFeb 11

@wingo yeah, it seems like a hard problem, PyPy's profiler is also in a bit of a weird state always, and our former ui is just gone.

I really don't get why nobody that I can find has done a graphviz based call graph though, like kcachegrind has it. It such a super useful tool.

Show threadStefan MarrFeb 11
@cfbolz @wingo I think PyCharm's looks similar? https://www.jetbrains.com/help/pycharm/read-the-profiling-report.html#view-graph
Read the profiler snapshot | PyCharm

PyCharm Help
Show threadCF Bolz-TereickFeb 11
@smarr @wingo goes in the right direction for sure!
Show threadZixian CaiFeb 11

@cfbolz @wingo have you tried MMTk’s tracing support? We also output in the JSON tracing format supported by Perfetto. https://github.com/mmtk/mmtk-core/tree/master/tools/tracing

Kunshan has written a case study using the tracing tools for performance debugging https://wks.github.io/blog/2023/10/04/proved-me-wrong.html

mmtk-core/tools/tracing at master · mmtk/mmtk-core

Memory Management ToolKit. Contribute to mmtk/mmtk-core development by creating an account on GitHub.

GitHub
Show threadAndy WingoFeb 11
@caizixian @cfbolz nice, will look! enjoyed the paper, btw!
Show threadZixian CaiFeb 11
@wingo @cfbolz I’m glad you enjoyed it. It was led by Claire as one of her undergraduate research projects. Very impressive work.