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

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Message-ID: <Z9iHiTv_ud6GEhJh@x1>
Date: Mon, 17 Mar 2025 17:35:21 -0300
From: Arnaldo Carvalho de Melo <acme@...nel.org>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Chun-Tse Shao <ctshao@...gle.com>, 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 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.

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?

Anyway, the series as is seems ok.

I'll test a bit more and send my Tested-by

- Arnaldo