Messages in this thread | | | Date | Wed, 20 Jan 2010 12:26:26 -0200 | From | Arnaldo Carvalho de Melo <> | Subject | Re: [PATCH] perf tools: fix write_event() |
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Em Wed, Jan 20, 2010 at 03:14:57PM +0100, Peter Zijlstra escreveu: > On Wed, 2010-01-20 at 12:09 -0200, Arnaldo Carvalho de Melo wrote: > > Em Wed, Jan 20, 2010 at 02:44:56PM +0100, Peter Zijlstra escreveu: > > > On Wed, 2010-01-20 at 14:41 +0100, Peter Zijlstra wrote: > > > > Uhm, how why? it didn't used to know about events and just copied the > > > > data. > > > > > > looks like acme wrecked it in f5a2c3dc.. anyway the fix is wrong, record > > > should not know or care about the actual events and simply write data > > > out. > > > > Oh well, I guess then we should do that after record finishes, > > reprocessing all the data in the file. > > Why do we need it at all? > > Can't report/archive/etc.. sort all this out?
We need to record the buildids at record time, preferrably at PERF_RECORD_MMAP time, from the kernel, for long running, low frequency sessions were DSOs may be updated.
Or for when a developer is updating his binary and doing perf record runs to then use perf diff:
perf record ./myapp vi myapp.c make perf record ./myapp perf diff
Works now because the first 'perf record' saved a copy of myapp so that 'perf diff', finding the right build-id in ~/.debug/.build-id/ can do the right thing.
But till we send the buildid in an extended PERF_RECORD_MMAP event sent from the kernel, I try to reduce the window by doing this at record time.
The current way of intercepting events at write_event() is deemed broken, so I can do it atexit(), when we go to write the header, but this will hurt because we'll have to reprocess it all.
Yes, since we'd still have the window, we could do it on perf archive, but it would be an extra explicit step and since I think the right place to do this is at perf record (with the kernel injecting the buildid, if present in the binary being loaded), I'd prefer to keep it that way.
Then work on having the buildid stored in some suitable kernel data structure and injected in the PERF_RECORD_MMAP event.
- Arnaldo
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