linux-kernel - Re: [PATCH v2 2/5] perf pmu: Support more complex PMU event aliasing

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Date:   Thu, 20 Jun 2019 20:25:19 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     John Garry <john.garry@...wei.com>
Cc:     peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
        alexander.shishkin@...ux.intel.com, namhyung@...nel.org,
        tmricht@...ux.ibm.com, brueckner@...ux.ibm.com,
        kan.liang@...ux.intel.com, ben@...adent.org.uk,
        mathieu.poirier@...aro.org, mark.rutland@....com,
        will.deacon@....com, linux-kernel@...r.kernel.org,
        linuxarm@...wei.com, linux-arm-kernel@...ts.infradead.org,
        zhangshaokun@...ilicon.com
Subject: Re: [PATCH v2 2/5] perf pmu: Support more complex PMU event aliasing

On Mon, Jun 17, 2019 at 10:06:08AM +0100, John Garry wrote:
> On 16/06/2019 10:58, Jiri Olsa wrote:
> > On Fri, Jun 14, 2019 at 10:08:00PM +0800, John Garry wrote:
> > > The jevent "Unit" field is used for uncore PMU alias definition.
> > > 
> > > The form uncore_pmu_example_X is supported, where "X" is a wildcard,
> > > to support multiple instances of the same PMU in a system.
> > > 
> > > Unfortunately this format not suitable for all uncore PMUs; take the Hisi
> > > DDRC uncore PMU for example, where the name is in the form
> > > hisi_scclX_ddrcY.
> > > 
> > > For the current jevent parsing, we would be required to hardcode an uncore
> > > alias translation for each possible value of X. This is not scalable.
> > > 
> > > Instead, add support for "Unit" field in the form "hisi_sccl,ddrc", where
> > > we can match by hisi_scclX and ddrcY. Tokens in Unit field are
> > > delimited by ','.
> > > 
> > > Signed-off-by: John Garry <john.garry@...wei.com>
> > > ---
> > >  tools/perf/util/pmu.c | 39 ++++++++++++++++++++++++++++++++++-----
> > >  1 file changed, 34 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/tools/perf/util/pmu.c b/tools/perf/util/pmu.c
> > > index 7e7299fee550..bc71c60589b5 100644
> > > --- a/tools/perf/util/pmu.c
> > > +++ b/tools/perf/util/pmu.c
> > > @@ -700,6 +700,39 @@ struct pmu_events_map *perf_pmu__find_map(struct perf_pmu *pmu)
> > >  	return map;
> > >  }
> > > 
> > > +static bool pmu_uncore_alias_match(const char *pmu_name, const char *name)
> > > +{
> > > +	char *tmp, *tok, *str;
> > > +	bool res;
> > > +
> > > +	str = strdup(pmu_name);
> > > +	if (!str)
> > > +		return false;
> > > +
> > > +	/*
> > > +	 * uncore alias may be from different PMU with common
> > > +	 * prefix or matching tokens.
> > > +	 */
> > > +	tok = strtok_r(str, ",", &tmp);
> > > +	if (strncmp(pmu_name, tok, strlen(tok))) {
> > 
> 
> Hi Jirka,

heya,
sry for late reply

> 
> > if tok is NULL in here we crash
> > 
> 
> As I see, tok could not be NULL. If str contains no delimiters, then we just
> return same as str in tok.
> 
> Can you see tok being NULL?

well, if there's no ',' in the str it returns NULL, right?
and IIUC this function is still called for standard uncore
pmu names

> 
> > > +		res = false;
> > > +		goto out;
> > > +	}
> > > +
> > > +	for (; tok; name += strlen(tok), tok = strtok_r(NULL, ",", &tmp)) {
> > 
> > why is name shifted in here?
> 
> I want to ensure that we match the tokens in order and also guard against
> possible repeated token matches in 'name'.

i might not understand this correctly.. so

str is the alias name that can contain ',' now, like:
  hisi_sccl,ddrc

and name is still pmu with no ',' ... please make this or
proper version that in some comment

thanks,
jirka