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

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Date:   Thu, 15 Nov 2018 21:02:10 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     "Liang, Kan" <kan.liang@...ux.intel.com>
Cc:     acme@...nel.org, mingo@...hat.com, peterz@...radead.org,
        linux-kernel@...r.kernel.org, namhyung@...nel.org,
        ak@...ux.intel.com
Subject: Re: [PATCH 1/2] perf vendor events: Add stepping in CPUID string for
 x86

On Thu, Nov 15, 2018 at 10:53:42AM -0500, Liang, Kan wrote:
> 
> > > > > +	/*
> > > > > +	 * 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.

ok, let's keep your way

jirk