Hi Steve, On Wed, 2021-02-24 at 11:54 -0500, Steven Rostedt wrote: > Hi Viktor, > > While doing some tests to trace-cmd, I found that the trace-cmd record was > broken for latency tracers, and has been for some time. That's probably > because nobody has been using it for such. > > That is, trace-cmd record is mostly used for "flyrecord" which is the > constant recording of tracing. But if the user records one of the latency > tracers (preemptirqsoff, wakeup_rt, etc), then it switches to "latency" > mode and only takes a snapshot at the end of the recording. This is what I > found to be broken, because it reset the tracing before taking the > snapshot and lost whatever it was recording. Nobody seemed to complain > about it, so I guess nobody cared. > I have used trace-cmd but I did not know about this feature. Somehow I had assumed that trace-cmd would not deal with those tracers that work in overwrite mode. > The fix is simple, and I was about to do so, but then I thought about your > latency-collector tool, and thought that should be exactly what trace-cmd > should do for such tracers. That is, instead of just taking a snapshot of > the latency at the end of the recording (which it was suppose to do now), > it should act like your latency-collector tool, and take snapshots > every time there's a new latency. > > My question to you is, would you like to work on adding that feature to > trace-cmd? I would be interested to work on the feature but I would probably need permission from my employer, also in case I do it as a spare time project. For this reason, I will need some time come to a decision. I will get back to you when I know the answer. > > git://git.kernel.org/pub/scm/utils/trace-cmd/trace-cmd.git > > (which requires the libtracefs and libtracevent libraries). > > I'm thinking if someone were to do: > > trace-cmd record -p wakeup_rt > > It would then act just like the latency-collector and record every new > instance of a latency into the trace.dat file, where: > > trace-cmd report > > would then nicely format that data for the user. > > Thoughts? It seems like trace-cmd is mostly GPL-2.0. The latency-collector is also GPL- 2.0, so I guess that it would be possible to take snippets of code and inspiration from it. Would you allow the hackish random algorithm to be used in trace-cmd? I mean the "--random" option in latency-collector. best regards, Viktor > > -- Steve
|