On 2023-12-09 22:54, Steven Rostedt wrote: [...]
Basically, events to the tracing subsystem are limited to just under a PAGE_SIZE, as the ring buffer is split into "sub buffers" of one page size, and an event can not be bigger than a sub buffer. This allows users to change the size of a sub buffer by the order: echo 3 > /sys/kernel/tracing/buffer_subbuf_order Will make each sub buffer a size of 8 pages, allowing events to be almost as big as 8 pages in size (sub buffers do have meta data on them as well, keeping an event from reaching the same size as a sub buffer).
Specifying the "order" of subbuffer size as a power of two of number of pages is a poor UX choice for a user-facing ABI. I would recommend allowing the user to specify the size in bytes, and internally bump to size to the next power of 2, with a minimum of PAGE_SIZE. Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. https://www.efficios.com
