Messages in this thread | | | Date | Sun, 27 Jun 2021 19:27:12 +0200 | From | Jiri Olsa <> | Subject | Re: [RFC 00/10] perf: Add build id parsing fault detection/fix |
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On Thu, Jun 24, 2021 at 01:44:43PM +0200, Michael Petlan wrote: > On Wed, 23 Jun 2021, Namhyung Kim wrote: > > Hi Jiri, > > > > Thanks for your work! > > > > On Tue, Jun 22, 2021 at 2:19 PM Jiri Olsa <jolsa@redhat.com> wrote: > > > > > > On Tue, Jun 22, 2021 at 03:14:04PM -0300, Arnaldo Carvalho de Melo wrote: > > > > Em Tue, Jun 22, 2021 at 10:47:54AM -0700, Ian Rogers escreveu: > > > > > On Tue, Jun 22, 2021 at 10:39 AM Arnaldo Carvalho de Melo > > > > > <acme@kernel.org> wrote: > > > > > > > > > > > > Em Tue, Jun 22, 2021 at 05:39:08PM +0200, Jiri Olsa escreveu: > > > > > > > hi, > > > > > > > this *RFC* patchset adds support to detect faults during > > > > > > > mmap2's build id parsing and a way to fix such maps in > > > > > > > generated perf.data. > > > > > > > > > > > > > > It adds support to record build id faults count for session > > > > > > > and store it in perf.data and perf inject support to find > > > > > > > these maps and reads build ids for them in user space. > > > > > > > > > > > > > It's probably best explained by the workflow: > > > > > > > > > > > > > > Record data with --buildid-mmap option: > > > > > > > > > > > > > > # perf record --buildid-mmap ... > > > > > > > ... > > > > > > > [ perf record: Woken up 1 times to write data ] > > > > > > > [ perf record: Failed to parse 4 build ids] > > > > > > > [ perf record: Captured and wrote 0.008 MB perf.data ] > > > > > > > > > > > > > > Check if there's any build id fault reported: > > > > > > > > > > > > > > # perf report --header-only > > > > > > > ... > > > > > > > # build id mmap stats: FAULTS 4, LOST 0, NOT FIXED > > > > > > > > > > > > > > There is, check the stats: > > > > > > > > > > > > > > # perf report --stat > > > > > > > > > > > > > > Aggregated stats: > > > > > > > TOTAL events: 104 > > > > > > > .... > > > > > > > BUILD_ID fails: 4 (14.3%) > > > > > > > > > > > > > > Yep, let's fix it: > > > > > > > > > > > > > > # perf inject --buildid-mmap2 -i perf.data -o perf-fixed.data > > > > > > > > > > > > Can we make it possible to automate this with --fixup-buildids or a > > > > > > perfconfig 'record' knob? > > > > > > > > > > > > This would entail requesting that build-ids that _fail_ be sent to the > > > > > > side-band thread we have in 'perf record', this way we wouldn't have to > > > > > > traverse the whole perf.data file, be it with 'perf-record' at the end > > > > > > of a session with faulty build ids, or in a similar fashion using 'perf > > > > > > inject' as you suggest. > > > > > > > > > > > > I even think that we can have all these modes and let the user to decide > > > > > > how important is this for them and how convenient they want the whole > > > > > > process to be. > > > > > > right, that might be good to decide first.. because as I said, > > > I never hit faulted build id, so it probably needs the special > > > setup you guys are using.. could you try on your setup and check > > > how many faulted build ids you see? > > > > Did you check data mmaps? It might be easy to get faults > > from data files and we don't know if it's an ELF or not > > before reading the ELF header in the first page. > > Hi. Long ago, I have noticed samples pointing to purely data files, > such as if the program execution was sampled just in the middle of > them. However, these files couldn't certainly contain any executable > code... It was quite hard to reproduce this. > > Maybe what Namhyung says might have been a culprit for it? Just an > idea...
yea, that sounds bad.. I guess you can no longer reproduce?
thanks, jirka
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