Messages in this thread | | | Date | Mon, 15 Jul 2013 09:14:04 +0300 | From | Adrian Hunter <> | Subject | Re: [PATCH V5 09/12] perf: make events stream always parsable |
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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).
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