On 11/07/13 18:43, David Ahern wrote: > On 7/11/13 7:12 AM, Adrian Hunter wrote: >> The event stream is not always parsable because the format of a sample >> is dependent on the sample_type of the selected event. When there >> is more than one selected event and the sample_types are not the >> same then parsing becomes problematic. A sample can be matched to its >> selected event using the ID that is allocated when the event is opened. >> Unfortunately, to get the ID from the sample means first parsing it. > > Here's an alternative suggestion -- one that does not involve changing the > kernel API or requiring a common denominator in sample_type options.
The kernel API is designed to be extensible. Extending it in a way that is perhaps unexpected but nevertheless backward compatible, is an appropriate solution. > > perf handles event streams through an mmap which can be directly tied to an > evsel (a single event) when the mmap is created. ie., when events are read > we know exactly which evsel they correspond to. (See > perf_evlist__mmap_per_cpu and perf_evlist__mmap_per_thread and add struct > perf_evsel *evsel entry to struct perf_mmap). > > Commands like perf-record can inject a user event into the stream and hence > the data file every time the evsel changes while walking all of the mmap's > reading events -- very similar to the way finished round is done. The event > would only contain a perf_event_header which is 8 bytes so this does not add > a lot to a data file. As an optimization the evsel event could only be > injected if the sample_types differ. > > Live commands would just use the evsel connected to the mmap -- no lookups > needed which would simplify things a bit processing the events. > > In short, the information to associate event streams to an event (evsel) is > currently available -- it's just being discarded in the many layers. > > I'll try to whip up some code that implements this in the next few days. > > David > > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
