On Tue, Apr 20, 2021 at 5:55 AM Steven Rostedt <[email protected]> wrote: [..] > > > So yes, function tracing now allows setting a filter to trace only the > > > functions for a given module, and if that module is not yet loaded, it > > > stores the filter until it is. > > > > Ah, thanks for the pointer. So if I wanted to convert a kernel command like: > > > > libnvdimm.dyndbg > > > > ...it would be something like: > > > > ftrace=function ftrace_filter=:mod:libnvdimm > > Hmm, that may not work, but if it doesn't, it would be trivial to add it. > > > > > ...and then "cat /sys/kernel/tracing/trace" instead of "dmesg" to > > retrieve... assuming only "got here" style debug was being attempted. > > > > > To do something similar for tracepoints, I think we still need to add it > > > as > > > a module parameter. > > > > The dev_dbg() filter language is attractive, it's too bad > > Not sure what you mean by that. What filter language. Tracepoints do have a > pretty good filtering too.
I'm trying to replicate dev_dbg() usability with tracing. So, when people say "don't use dev_dbg() for that" that tracing can reliably replace everything that dev_dbg() was offering. What I think that looks like is the ability to turn on function tracing by a function name glob in addition to any tracepoints in those same functions all from the kernel boot command line, or a module parameter. > > trace_printk() has such a high runtime cost as combining dynamic-debug > > and tracing would seem to be a panacea. > > trace_printk() has a high runtime cost? Besides that it's not allowed on > production code (see nasty banner), it is made to be extremely fast. > Although, it does do sprintf() work. I was referring to the banner. dev_dbg() does not have that production code restriction. > Would adding automatic module parameters be an issue? That is, you can add > in the insmod command line a parameter that will enable tracepoints. We > could have a way to even see them from the modinfo. I think I had that > working once, and it wasn't really that hard to do. Yeah, that's what you seemed to have working at the beginning of this thread: https://lore.kernel.org/lkml/[email protected]/
