linux-kernel - Re: [PATCH v2 1/2] perf record: Add 8-byte aligned event type PERF_RECORD

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Message-ID: <aCePEgXqcfQ9BCQy@x1>
Date: Fri, 16 May 2025 16:16:34 -0300
From: Arnaldo Carvalho de Melo <acme@...nel.org>
To: Chun-Tse Shao <ctshao@...gle.com>
Cc: Namhyung Kim <namhyung@...nel.org>, linux-kernel@...r.kernel.org,
	peterz@...radead.org, mingo@...hat.com, mark.rutland@....com,
	alexander.shishkin@...ux.intel.com, jolsa@...nel.org,
	irogers@...gle.com, adrian.hunter@...el.com,
	kan.liang@...ux.intel.com, terrelln@...com, leo.yan@....com,
	james.clark@...aro.org, christophe.leroy@...roup.eu,
	ben.gainey@....com, linux-perf-users@...r.kernel.org
Subject: Re: [PATCH v2 1/2] perf record: Add 8-byte aligned event type
 PERF_RECORD_COMPRESSED2

On Fri, May 16, 2025 at 10:10:27AM -0700, Chun-Tse Shao wrote:
> Ping.
> 
> For suggestions from Namhyung and Arnaldo, it was merged in:
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/commit/?h=perf-tools-next&id=b1b26ce8bb0eab1d058353ab6fa1a2b652a9a020

Testing it now, fixed up this:

+It is deprecated and new files should use PERF_RECORD_COMPRESSED2 to gurantee
                                                                      guarantee
+8-byte alignment.

- Arnaldo
 
> Thanks,
> CT
> 
> On Mon, Mar 17, 2025 at 10:13 PM Namhyung Kim <namhyung@...nel.org> wrote:
> >
> > Hello,
> >
> > On Mon, Mar 17, 2025 at 06:49:32PM -0300, Arnaldo Carvalho de Melo wrote:
> > > On Mon, Mar 17, 2025 at 02:45:39PM -0700, Chun-Tse Shao wrote:
> > > > On Mon, Mar 17, 2025 at 1:35 PM Arnaldo Carvalho de Melo
> > > > <acme@...nel.org> wrote:
> > > > >
> > > > > On Mon, Mar 17, 2025 at 09:46:40AM -0700, Namhyung Kim wrote:
> > > > > > On Mon, Mar 17, 2025 at 01:17:46PM -0300, Arnaldo Carvalho de Melo wrote:
> > > > > > > On Mon, Mar 17, 2025 at 12:52:09PM -0300, Arnaldo Carvalho de Melo wrote:
> > > > > > > > Checking the discussion and the patch.
> > > > > > >
> > > > > > > My first impression yesterday when I saw this on the smartphone was: how
> > > > > > > will an old perf binary handle the new PERF_RECORD_COMPRESSED2? Will it
> > > > > > > ignore it while emitting a warning, since it can be skipped and then
> > > > > > > what we will get a partial view?
> > > > > > >
> > > > > > > Having some session output showing how an older perf binary handles
> > > > > > > PERF_RECORD_COMPRESS2 would be informative.
> > > > > >
> > > > > > I think it'll show the below warning:
> > > > > >
> > > > > >   <offset> [<size>]: failed to process type: 83
> > > > >
> > > > > Right that is what I got:
> > > > >
> > > > > ⬢ [acme@...lbox perf-tools-next]$ perf.old script -i /tmp/perf.data.ck8
> > > > > 0xbf0 [0x250]: failed to process type: 83 [Invalid argument]
> > > > > ⬢ [acme@...lbox perf-tools-next]$
> > > > >
> > > > > I think we should change that to something more informative, like:
> > > > >
> > > > > 0xbf0 [0x250]: failed to process unknown type 83, please update perf.
> >
> > That would be nice, but there are cases it can fail even without new
> > record formats.  So it should also check if the type number is greater
> > than or equal to the max.
> >
> > > > >
> > > > > And then does it stop at that record it doesn't grok?
> > > > >
> > > > >         if ((skip = perf_session__process_event(session, event, head, "pipe")) < 0) {
> > > > >                 pr_err("%#" PRIx64 " [%#x]: failed to process type: %d\n",
> > > > >                        head, event->header.size, event->header.type);
> > > > >                 err = -EINVAL;
> > > > >                 goto out_err;
> > > > >         }
> > > > >
> > > > >         head += size;
> > > > >
> > > > > So we're stopping there.
> > > > >
> > > > > Maybe we can just warn and skip?
> > > >
> > > > Thank you Arnaldo, it is a good suggestion and I will work on this later.
> > >
> > > Thank you for considering that, really appreciated!
> >
> > It would be hard to process misaligned data though.  Probably we also
> > want to add a check to make sure it's properly aligned.
> >
> > Thanks,
> > Namhyung
> >
> > >
> > > perf deals with so much stuff and code flux that all the help that we
> > > can get is what is needed for it to continue to be relevant and useful.
> > >
> > > After all what is the point of a tool that produces bad results? :-)
> > >
> > > - Arnaldo
> > >
> > > > -CT
> > > >
> > > > >
> > > > > Anyway, the series as is seems ok.
> > > > >
> > > > > I'll test a bit more and send my Tested-by
> > > > >
> > > > > - Arnaldo