linux-kernel - Re: [RFC PATCH 6/6] perf cs-etm: Add warnings for missing DSOs

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Message-ID: <20210803140122.GC247709@leoy-ThinkPad-X240s>
Date:   Tue, 3 Aug 2021 22:01:22 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     James Clark <james.clark@....com>, mathieu.poirier@...aro.org,
        coresight@...ts.linaro.org, linux-perf-users@...r.kernel.org,
        suzuki.poulose@....com, mike.leach@...aro.org,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        John Garry <john.garry@...wei.com>,
        Will Deacon <will@...nel.org>, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC PATCH 6/6] perf cs-etm: Add warnings for missing DSOs

On Tue, Aug 03, 2021 at 10:24:09AM -0300, Arnaldo Carvalho de Melo wrote:
> Em Mon, Aug 02, 2021 at 11:41:45PM +0800, Leo Yan escreveu:
> > On Thu, Jul 29, 2021 at 04:58:05PM +0100, James Clark wrote:
> > > Currently decode will silently fail if no binary data is available for
> > > the decode. This is made worse if only partial data is available because
> > > the decode will appear to work, but any trace from that missing DSO will
> > > silently not be generated.
> > > 
> > > Add a UI popup once if there is any data missing, and then warn in the
> > > bottom left for each individual DSO that's missing.
> > > 
> > > Signed-off-by: James Clark <james.clark@....com>
> > > ---
> > >  tools/perf/util/cs-etm.c | 10 +++++++++-
> > >  1 file changed, 9 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
> > > index 32ad92d3e454..e6851260d059 100644
> > > --- a/tools/perf/util/cs-etm.c
> > > +++ b/tools/perf/util/cs-etm.c
> > > @@ -746,8 +746,16 @@ static u32 cs_etm__mem_access(struct cs_etm_queue *etmq, u8 trace_chan_id,
> > >  
> > >  	len = dso__data_read_offset(al.map->dso, machine, offset, buffer, size);
> > >  
> > > -	if (len <= 0)
> > > +	if (len <= 0) {
> > > +		ui__warning_once("CS ETM Trace: Missing DSO. Use 'perf archive' to export data from the traced system.\n");
> > > +		if (!al.map->dso->auxtrace_warned) {
> > > +			pr_err("CS ETM Trace: Debug data not found for address %#"PRIx64" in %s\n",
> > > +				    address,
> > > +				    al.map->dso->long_name ? al.map->dso->long_name : "Unknown");
> > > +			al.map->dso->auxtrace_warned = true;
> > > +		}
> > 
> > This is very useful.
> > 
> > Just one comment: in particularly if the perf fails to find the kernel
> > symbols, the user needs to enable config "CONFIG_PROC_KCORE=y" or
> > specify option "-k /path/to/vmlinux".  In this case, using 'perf
> > archive' is not helpful.  So I think the UI warning can be imporved
> > like:
> > 
> >         ui__warning_once("CS ETM Trace: Missing DSO. Use 'perf archive' to export data from the traced system.\n"
> >                          " Enable CONFIG_PROC_KCORE or use option '-k /path/to/vmlinux' for kernel symbols\n");
> 
> one can also use debuginfod-client, which, as time passes, probably will
> be the main way of finding DSOs now that we have build-ids in
> PERF_RECORD_MMAP2 and debuginfod servers such as:
> 
> export DEBUGINFOD_URLS=https://debuginfod.fedoraproject.org/

If so, maybe should use more general description for missing DSO.

> https://fedoraproject.org/wiki/Debuginfod
>  
> > With this improvement, the patch looks good to me:
> > 
> > Reviewed-by: Leo Yan <leo.yan@...aro.org>
> 
> Does this apply to the other 5 patches in this series?

I finished to reivew patches 01, 04, 05, 06/06, so my review tag can
apply on these patches.  Current patch 06/06 needs James to improve for
the comments.

Thanks,
Leo