Thanks Ingo, On Monday 20 February 2017 02:12 PM, Ingo Molnar wrote: > * Ravi Bangoria <ravi.bango...@linux.vnet.ibm.com> wrote: > >> What should be the behavior of the tool? Should it record only one >> 'sdt_libpthread:mutex_entry' which exists in uprobe_events? Or it >> should record all the SDT events from libpthread? We can choose either >> of two but both the cases are ambiguous. > They are not ambiguous really if coded right: just pick one of the outcomes > and > maybe print a warning to inform the user that something weird is going on > because > not all markers are enabled? > > As a user I'd expect 'perf record' to enable all markers and print a warning > that > the markers were in a partial state. This would result in consistent > behaviour.
Yes, makes sense. > Does it make sense to only enable some of the markers that alias on the same > name? > If not then maybe disallow that in perf probe - or change perf probe to do > the > same thing as perf record. 'perf probe' is doing that correctly. It fetches all events with given name from probe-cache and creates entries for them in uprobe_events. The problem is the 2-step process of adding probes and then recording, allowing users to select individual markers to record on. > > I.e. this is IMHO an artificial problem that users should not be exposed to > and > which can be solved by tooling. > > In particular if it's possible to enable only a part of the markers then perf > record not continuing would be a failure mode: if for example a previous perf > record session segfaulted (or ran out of RAM or was killed in the wrong > moment or > whatever) then it would not be possible to (easily) clean up the mess. Agreed. We need to make this more robust. > >> Not allowing 'perf probe' for SDT event will solve all such issues. >> Also it will make user interface simple and consistent. Other current >> tooling (systemtap, for instance) also do not allow probing individual >> markers when there are multiple markers with the same name. > In any case if others agree with your change in UI flow too then it's fine by > me, > but please make it robust, i.e. if perf record sees partially enabled probes > it > should still continue. @Masami, can you please provide your thoughts as well. Thanks, Ravi
