Messages in this thread | | | Date | Mon, 15 Jul 2013 15:09:34 +0300 | From | Adrian Hunter <> | Subject | Re: [PATCH V5 09/12] perf: make events stream always parsable |
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On 15/07/13 14:53, Stephane Eranian wrote: > On Mon, Jul 15, 2013 at 8:14 AM, Adrian Hunter <adrian.hunter@intel.com> wrote: >> On 12/07/13 17:55, Peter Zijlstra wrote: >>> On Fri, Jul 12, 2013 at 03:56:01PM +0300, Adrian Hunter wrote: >>>>> There's events where this isn't a possible location; take PERF_RECORD_MMAP for >>>>> instance; the tail is the complete filename. >>>> >>>> PERF_RECORD_MMAP falls in the category I have called non-sample events. >>>> Those events are appended with an ID sample. perf tools parses the ID >>>> sample backwards from header.size. So the ID is at the last position >>>> relative to header.size >>> >>> But why? Why make it different per PERF_RECORD type? >> >> There have always been two formats: >> >> 1. PERF_RECORD_SAMPLE as defined by perf_output_sample() >> >> 2. everything else as defined by __perf_event__output_id_sample() >> >> The two formats are not the same, and there is no reason for them to be. >> >> PERF_RECORD_SAMPLE is parsed forwards, so the ID is at the first position. >> >> ID samples are parsed backwards, so the ID is at the last position (i.e. the >> first position parsed). >> > I am missing something here. > Why do we need an event ID for RECORD_MMAP records? > I understand those are requested by events, but do we care which one? > The information is global to the monitored process and not specific to an event.
The ID sample has, for example, the time, so you still have to parse it - which means you need the sample_type which means you need the id.
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