linux-kernel - Re: [PATCH 2/9] perf tools: Support the auxiliary event

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Message-ID: <20210203213028.GY854763@kernel.org>
Date:   Wed, 3 Feb 2021 18:30:28 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     "Liang, Kan" <kan.liang@...ux.intel.com>
Cc:     mingo@...nel.org, linux-kernel@...r.kernel.org,
        peterz@...radead.org, eranian@...gle.com, namhyung@...nel.org,
        jolsa@...hat.com, ak@...ux.intel.com, yao.jin@...ux.intel.com,
        maddy@...ux.vnet.ibm.com
Subject: Re: [PATCH 2/9] perf tools: Support the auxiliary event

Em Wed, Feb 03, 2021 at 04:20:38PM -0500, Liang, Kan escreveu:
> 
> 
> On 2/3/2021 3:02 PM, Arnaldo Carvalho de Melo wrote:
> > Em Tue, Feb 02, 2021 at 12:09:06PM -0800,kan.liang@...ux.intel.com  escreveu:
> > > From: Kan Liang<kan.liang@...ux.intel.com>
> > > diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> > > index c26ea822..c48f6de 100644
> > > --- a/tools/perf/util/evsel.c
> > > +++ b/tools/perf/util/evsel.c
> > > @@ -2689,6 +2689,9 @@ int evsel__open_strerror(struct evsel *evsel, struct target *target,
> > >   		if (perf_missing_features.aux_output)
> > >   			return scnprintf(msg, size, "The 'aux_output' feature is not supported, update the kernel.");
> > >   		break;
> > > +	case ENODATA:
> > > +		return scnprintf(msg, size, "Cannot collect data source with the load latency event alone. "
> > > +				 "Please add an auxiliary event in front of the load latency event.");
> > Are you sure this is the only case where ENODATA comes out from
> > perf_event_open()? Well, according to your comment in:
> > 
> >    61b985e3e775a3a7 ("perf/x86/intel: Add perf core PMU support for Sapphire Rapids")
> > 
> > It should be at that point in time, so its safe to merge as-is, but then
> > I think this is fragile, what if someone else, in the future, not
> > knowing that ENODATA is supposed to be used only with that ancient CPU,
> > Sapphire Rapids, uses it?:-)
> > 
> > Please consider adding a check before assuming ENODATA is for this
> > specific case.
> 
> Sure, I will add a check in V2.

Do it as a separate patch, on top of what is now in tmp.perf/core.

https://git.kernel.org/pub/scm/linux/kernel/git/acme/linux.git/log/?h=tmp.perf/core

- Arnaldo