Magic-trace – High-resolution traces of what a process is doing

Re:Magic-trace – High-resolution traces of what a process is... by brendangregg on Saturday April 23, 2022 @02:12AM (#31131873)

Thanks, good to see a new perf tool (and not just another procfs top clone :-). I've started using processor trace in the cloud, thanks to bare-metal instances, but for years I couldn't touch it (not available in VMs). There's a wealth of new information it provides, and we need better tooling on top of it, like magic-trace.

Glad to see "overhead" mentioned and quantified. I'd put the 2-10% at the top though, as that's heavy handed for some environments (can trigger a production fail-over).

I see magic-trace has implemented what some call "flame charts" (time on the x-axis) and not "flame graphs" (alphabet on the x-axis). The best tools do both (e.g., TraceCompass). Please do both! Will make seeing the big picture easy (flame graphs) and then zooming into time-based patterns easy too (flame charts).

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Re:Magic-trace – High-resolution traces of what a process is... by cgaebel on Saturday April 23, 2022 @07:19AM (#31133267)

We are similarly sad about how unavailable Intel PT is in VMs. In 2022, being unavailable on Macs and VMs raises the barrier to entry extraordinarily high for many people in our target audience. Not sure if working outside of work is your cup of tea, but we've found Intel NUCs to be <$1000 and an unobtrusive way to play with these features at home.

Good point about overhead. I've moved the 2%-10% number front and center, and wrote up a bit more detail about where that comes from in a new wiki page: https://github.com/janestreet/magic-trace/wiki/Overhead

We'll think about adding flame graphs. We unfortunately have little experience writing responsive web UIs, the excellent Perfetto developers did all of the heavy lifting on that front. But who knows, maybe an enterprising Open Source Contributor could help us out. I see Matt Godbolt was asking questions in their discord the other day...

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Re:Magic-trace – High-resolution traces of what a process is... by lalitmaganti on Saturday April 23, 2022 @01:39PM (#31136390)

(Perfetto developer here)

The Perfetto UI already supports flamegraphs btw (we use it for memory profiling and CPU stack sampling). We've never bothered to implement it for userspace slices because we've never had high frequency data there to make that a worthwhile view of the data.

Contributions for this upstream are very welcome :)

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