Thanks Arnaldo, I'm working on this but it's taking bit longer time. Will post out a patch within few days.
Ravi On Monday 20 February 2017 07:41 PM, Arnaldo Carvalho de Melo wrote: > Em Mon, Feb 20, 2017 at 04:31:50PM +0530, Ravi Bangoria escreveu: >> Thanks Ingo, >> >> On Monday 20 February 2017 02:12 PM, Ingo Molnar wrote: >>> * Ravi Bangoria <[email protected]> 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. > So, the more streamlined one works for most people, i.e. just use perf > record, no need to perf probe anything. But, for people who "know what > they are doing", perf probe can be used first to control exactly which > SDT probes one wants in place, and then those will be used. > > We need to make sure that when processing the file there is information > that says which probes were in place and enabled in the record session, > tho. Is that possible? > >>> 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. > Right, disambiguating a 'probes left by a session that did auto-probing' > from a 'hey, those probes are there intentionally, just use those' is > important. > >>>> 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. > Yeah, if technically possible to allow both variants, we should leave > it up to users to decide what is best? > > I.e. most people will do auto-probing, not using 'perf probe' at all, > documentation should state the pitfalls in doing so. > > So, after writing the above, perhaps we should warn the user that > pre-existing probes are being used, as this will be the odd case? > > The normal flow will be just using perf record with SDT probes, that > will auto-probe them and remove on exit, or better drop a reference to > them, as simultaneous use also needs to be covered? > > - Arnaldo >
