linux-kernel - Re: [PATCH 1/2] perf tests: Fix switch tracking test for P4

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Date:   Sun, 4 Jun 2017 21:09:22 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Adrian Hunter <adrian.hunter@...el.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>,
        Michael Petlan <mpetlan@...hat.com>,
        lkml <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Namhyung Kim <namhyung@...nel.org>,
        David Ahern <dsahern@...il.com>,
        Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 1/2] perf tests: Fix switch tracking test for P4

On Fri, Jun 02, 2017 at 02:35:59PM +0300, Adrian Hunter wrote:
> On 01/06/17 16:11, Arnaldo Carvalho de Melo wrote:
> > Em Fri, May 26, 2017 at 02:31:40PM +0200, Jiri Olsa escreveu:
> >> The switch tracking test keeps failing on P4 cpu,
> >> when NMI watchdog is enabled.
> >>
> >> The reason is that P4 pmu uses substitute event for cycles
> >> when it's already taken (in our case by NMI watchdog), but
> >> this event does not give even results like cycles, and we
> >> could end up with no samples at all for our short
> >> measuring period.
> 
> Did you consider increasing the measuring period?

not really, in some cases I saw no samples generated for bigger
periods for another workloads, so I did not think of that in here,
but I'll check

SNIP

> >>  
> >>  static int spin_sleep(void)
> >>  {
> >> @@ -298,6 +299,27 @@ static int process_events(struct perf_evlist *evlist,
> >>  	return ret;
> >>  }
> >>  
> >> +static const char *get_hw_counter(void)
> >> +{
> >> +	const char *counter = "cycles:u";
> >> +	char *cpuid;
> >> +
> >> +	cpuid = get_cpuid_str();
> >> +
> >> +	/*
> >> +	 * P4 pmu uses substitute event for cycles if it's already
> >> +	 * taken, but it does not give even results like cycles,
> >> +	 * and we could end up with no samples at all for our short
> >> +	 * measuring period. Using "instructions:u" event instead,
> >> +	 * which seems to be stable enough.
> >> +	 */
> >> +	if (!strcmp("GenuineIntel-15-4", cpuid))
> 
> Why just model 4?  Isn't all family 15 P4?

I thought there's just one model.. but just based on the kernel code

> 
> >> +		counter = "instructions:u";
> >> +
> >> +	pr_debug("using '%s' HW counter");
> 
> tests/switch-tracking.c: In function ‘get_hw_counter’:
> tests/switch-tracking.c:319:2: error: format ‘%s’ expects a matching ‘char
> *’ argument [-Werror=format=]

omg.. sure ;-)

thanks,
jirka