Bug #1383
openThe "cpu_id" context (available for filters) is not discoverable by end users
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Description
I recently tried remembering how to filter by cpu_id when enabling an event, and found that there was not clear way to see that $ctx.cpu_id actually exists from the lttng man pages (other than a random example in the lttng-enable-event man page). AFAIU the man pages rely on lttng add-context --list to let the user discover the available contexts. This is likely because the cpu_id context is not available for the "add-context" command because it would be redundant with the implicit context already sampled with the buffers.
We may want to have some way to let users discovers those contexts which are filter-specific.
My use-case is to try to grab only traces for a few logical cpus (0-3) from my 384 logical cpus machine.
Updated by Erica Bugden 9 months ago
So my understanding based on the description is that this filter option is essentially not listed or described within the tool/documentation.
As a reference for the bug importance, are there several filter features that suffer from this problem? As in, other "off-menu" options that are difficult to discover.
Updated by Mathieu Desnoyers 9 months ago
AFAIR cpu_id is the only "special-case" at the moment.