linux-kernel - Re: [PATCH v8 2/4] perf inject: add jitdump mmap injection support

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Date:	Fri, 12 Feb 2016 17:43:10 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Andi Kleen <andi@...stfloor.org>, Jiri Olsa <jolsa@...hat.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Rose Belcher <cel@...ibm.com>,
	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>,
	Sonny Rao <sonnyrao@...omium.org>,
	John Mccutchan <johnmccutchan@...gle.com>,
	David Ahern <dsahern@...il.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Pawel Moll <pawel.moll@....com>
Subject: Re: [PATCH v8 2/4] perf inject: add jitdump mmap injection support

Em Fri, Feb 12, 2016 at 12:32:53PM -0800, Stephane Eranian escreveu:
> On Thu, Feb 11, 2016 at 2:16 PM, Arnaldo Carvalho de Melo <acme@...nel.org> wrote:
> > Em Mon, Feb 08, 2016 at 10:53:48AM -0800, Stephane Eranian escreveu:
> >> > I.e. the MMAP records for the kernel modules comes in ok, humm, because
> >> > probably you don't hook on PERF_RECORD_MMAP in perf-inject, just on MMAP2, and
> >> > in those the only difference is the second field, 0x6b98 -> 0x42a0, what is
> >> > that?

> >> I have both MMAP and MMAP2 hooks for the jit mode of perf inject.

> > IIRC the different in the offsets came from 'perf inject' not preserving
> > FINISHED_ROUND events.

> That's an oversight. Is there code to repipe this event already?

Unsure, please check
 
> >> > static void dump_event(struct perf_evlist *evlist, union perf_event *event,
> >> >                        u64 file_offset, struct perf_sample *sample)
> >> > {
> >> >         if (sample)
> >> >                 perf_evlist__print_tstamp(evlist, event, sample);
> >> >
> >> >         printf("%#" PRIx64 " [%#x]: PERF_RECORD_%s", file_offset,
> >> >                event->header.size, perf_event__name(event->header.type));
> >> >
> >> > File offset, what changed?
> >> >
> >> As for this, the offset is not recorded in the MMAP2 record, this is
> >> an artifact of the __perf_Session__process_events()
> >> which passes the file_offset in the perf.data file (read by mmapping).
> >> The offsets are changed because we inject
> >> new mmap records, and thus the existing MMAP may be moved to a later
> >> position in the file.
> >>
> >> Hope this helps.
> >
> > IIRC it was the missing FINISHED_ROUND, haven't checked if that was on
> > purpose an oversight or even if so if it ends up being harmless for most
> > workloads, have you tried this with long running or high sample freq?
> >
> Not yet, let me try.
> 
> >
> >> >
> >> > -0x7c18 [0x8]: event: 68
> >> > -.
> >> > -. ... raw event: size 8 bytes
> >> > -.  0000:  44 00 00 00 00 00 08 00                          D.......
> >> > -.
> >> > -0x7c18 [0x8]: PERF_RECORD_FINISHED_ROUND
> >> > -
> >> > -0x6a80 [0x28]: event: 9
> >> >
> >> > Humm, inject doesn't preserves PERF_RECORD_FINISHED_ROUND? Or user events in
> >> > general? On purpose?
> >
> > What about this question? Do you know? Oversight?
> >
> Oversight.
> 
> I pulled tip.git and jvmti does not compile anymore for me because of
> the alternative vs.
> update-java-alternatives problem.
> Is it the case that on Fedora, you do not have
> update-java-alternatives? If so, we could
> have the Makefile check if it exists and if not default to what you have.

right, we need to make it test and use what is available, here:

[root@...et ~]# dnf search alternatives
Last metadata expiration check performed 1:01:59 ago on Fri Feb 12
16:38:51 2016.
================================================================= N/S
Matched: alternatives
==================================================================
galternatives.noarch : Alternatives Configurator
ghc-base-unicode-symbols.x86_64 : Unicode alternatives for common
functions and operators
[root@...et ~]# rpm -qf `which update-alternatives`
chkconfig-1.7-1.fc23.x86_64
[root@...et ~]# rpm -ql chkconfig | grep alternativ
/etc/alternatives
/usr/sbin/alternatives
/usr/sbin/update-alternatives
/usr/share/man/man8/alternatives.8.gz
/usr/share/man/man8/update-alternatives.8.gz
/var/lib/alternatives