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Date: Mon, 11 Feb 2019 11:30:07 -0800 From: Stephane Eranian <eranian@...gle.com> To: Arnaldo Carvalho de Melo <acme@...nel.org> Cc: Jiri Olsa <jolsa@...hat.com>, Alexey Budankov <alexey.budankov@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, lkml <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...nel.org>, Namhyung Kim <namhyung@...nel.org>, Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, Adrian Hunter <adrian.hunter@...el.com>, Andi Kleen <ak@...ux.intel.com>, Song Liu <songliubraving@...com> Subject: Re: [RFC/PATCH 00/14] perf record: Add support to store data in directory Arnaldo, On Mon, Feb 11, 2019 at 10:55 AM Arnaldo Carvalho de Melo <acme@...nel.org> wrote: > > Em Mon, Feb 11, 2019 at 10:34:16AM -0800, Stephane Eranian escreveu: > > Jiri, > > > > On Mon, Feb 11, 2019 at 2:20 AM Jiri Olsa <jolsa@...hat.com> wrote: > > > > > > On Tue, Feb 05, 2019 at 02:37:27PM +0100, Jiri Olsa wrote: > > > > On Mon, Feb 04, 2019 at 02:44:37PM -0800, Stephane Eranian wrote: > > > > > Jiri, > > > > > > > > > > While you're looking at the output format, I think it would be good > > > > > time to simplify the code handling perf.data file. > > > > > Today, perf record can emit in two formats: file mode or pipe mode. > > > > > This adds complexity in the code and > > > > > is error prone as the file mode path is tested more than the pipe mode > > > > > path. We have run into multiple issues with > > > > > the pipe mode in recent years. There is no real reason why we need to > > > > > maintain two formats. If I recall, the pipe format > > > > > was introduced because on pipes you cannot lseek to update the headers > > > > > and therefore some of the information present as tables > > > > > updated on the fly needed to be generated as pseudo records by the > > > > > tool. I believe that the pipe format covers all the needs and could > > > > > supersede the file mode format. That would simplify code in perf > > > > > record and eliminate the risk of errors when new headers > > > > > are introduced. > > > > > > > > yep, I think we have almost all the features covered for pipe mode, > > > > and we have all necessary events to describe events features > > > > > > > > so with some effort we could switch off the superfluos file header > > > > and use only events to describe events ;-) make sense, I'll check > > > > on it > > > > > > so following features are not synthesized: > > > > > > FEAT_OPN(TRACING_DATA, tracing_data, false), > > > FEAT_OPN(BUILD_ID, build_id, false), > > > FEAT_OPN(BRANCH_STACK, branch_stack, false), > > > FEAT_OPN(AUXTRACE, auxtrace, false), > > > FEAT_OPN(STAT, stat, false), > > > FEAT_OPN(CACHE, cache, true), > > > > > What do you need for BRANCH_STACK? > > > > > I think all could be added and worked around with exception > > > of BUILD_ID, which we store at the end (after processing > > > all data) and we need it early in the report phase > > > > > Buildids are injected after the fact via perf inject when in pipe mode. > > > > > maybe it's time to re-think that buildid -> mmap event > > > association again, because it's pain in current implementation > > > as well > > > > > Sure, but what do you propose? > > this keeps resurfacing, the idea is to have the building go together > with the PERF_RECORD_MMAP3 event, i.e. as part of setting up an > executable mapping the loader would get the buildid and ask the kernel > to keep it aroung, then when a PERF_RECORD_MMAP needs to be issued, it > can include the build id, so tooling will not need to get it. > And how would the dynamic loader (ld.so) communicate the buildid to the kernel? How would that work for statically linked binaries. I think you're say the kernel would parse the ELF header looking for that note section and extract the buildid from there. Is that what you are proposing? > Alternatively, we would have a separate thread to process > PERF_RECORD_MMAP events, and as soon as it gets one from the kernel, > augment it straight away with the build-id it reads from the ELF file, > i.e. no need to have the kernel provide it, do it just like we do with > PERF_RECORD_BPF_EVENT, which reminds me Song probably already posted > thise bits... > But that would not work in pipe mode, wouldn't it? Unless that thread intercepts everything pushed to the pipe looking for MMAP records. > > > looks like bpf code is actualy getting build ids and storing > > > it for the callchains in kernel.. we can check if we can do > > > something similar for mmap events > > > > > > jirka > > -- > > - Arnaldo
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