Messages in this thread | | | Date | Thu, 25 Nov 2010 15:07:25 +0100 | Subject | Re: [RFC PATCHv3] perf tools: add event grouping capability to "perf stat" | From | Stephane Eranian <> |
| |
On Thu, Nov 25, 2010 at 3:02 PM, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote: > On Thu, 2010-11-25 at 14:19 +0100, Stephane Eranian wrote: > >> I think using PERF_SAMPLE_READ may expose a problem in the >> perf.data format. To correctly parse a sample created with SAMPLE_READ, >> you need to know the attr.read_format. But for that you need to know the >> event which caused the sample, but for that you need the SAMPLE_ID, >> and you don't know if it's there or not. In other words, there is a chicken >> and egg problem. >> >> I think the issue is that PERF_RECORD_SAMPLE is missing a mandatory >> piece of information: overflow event ID. This must a mandatory field, not >> optional as it is today. It is okay when you have only one group, but we'd >> like to go beyond that. > > > > I'm not sure I get it, there's both PERF_FORMAT_ID and PERF_SAMPLE_ID, > so afaict there's a working combination for what you want to do. > Ok, I had forgotten about PERF_SAMPLE_ID. But that means that if the number of groups > 1, then if you use PERF_SAMPLE_READ, you MUST also use PERF_SAMPLE_ID. Otherwise you cannot get back to the event that generated the sample and thus attr.read_format.
| |