Re: [PATCH 1/2] perf vendor events: Add stepping in CPUID string for x86

[Liang, Kan]

> > > > +	/*
> > > > +	 * Full CPUID format is required to identify a platform.
> > > > +	 * Error out if the cpuid string is incomplete.
> > > > +	 */
> > > > +	if (full_mapcpuid && !full_cpuid) {
> > > > +		pr_info("Invalid CPUID %s. Full CPUID is required, "
> > > > +			"vendor-family-model-stepping\n", cpuid);
> > > > +		return 1;
> > > > +	}
> > > > +
> > > > +	if (regcomp(&re, mapcpuid, REG_EXTENDED) != 0) {
> > > > +		/* Warn unable to generate match particular string. */
> > > > +		pr_info("Invalid regular expression %s\n", mapcpuid);
> > > > +		return 1;
> > > > +	}
> > > > +
> > > > +	match = !regexec(&re, cpuid, 1, pmatch, 0);
> > > > +	regfree(&re);
> > > > +	if (match) {
> > > > +		size_t match_len = (pmatch[0].rm_eo - pmatch[0].rm_so);
> > > > +		size_t cpuid_len;
> > > > +
> > > > +		/* If the full CPUID format isn't required,
> > > > +		 * ignoring the stepping.
> > > > +		 */
> > > > +		if (!full_mapcpuid && full_cpuid)
> > > > +			cpuid_len = strrchr(cpuid, '-') - cpuid;
> > > > +		else
> > > > +			cpuid_len = strlen(cpuid);
> > > > +
> > > > +
> > > > +		/* Verify the entire string matched. */
> > > > +		if (match_len == cpuid_len)
> > > > +			return 0;
> > >
> > > why is this necessary?
> >
> > It's from previous common code. As my understanding, it just double check
> > the matched strings. There is no harmful. So I keep it.
>
> right.. did you consider using the wildcard in the map file
> so it'd cover the stepping, having entries like:
>
>    GenuineIntel-6-1F-*,v2,nehalemep,core
>
> I haven't thought this one through, but seems we could bypass
> those '-stepping' checks.. but probably other changes would be
> necessary for the wildcard

If using wildcard, the full cpuid format is required for all platforms.
The script which using environment string "PERF_CPUID" will definitely 
be broken on all platforms.
This patch (non-wildcard) only breaks the script on Skylake server and 
Cascadelake server.

I think that's the only drawback of using wildcard.

Thanks,
Kan