Re: [PATCH 4/5] perf metricgroup: Support metric constraint

[Liang, Kan]

On 2/21/2020 8:09 AM, Jiri Olsa wrote:
> On Thu, Feb 20, 2020 at 11:14:09AM -0500, Liang, Kan wrote:
> > On 2/20/2020 6:35 AM, Jiri Olsa wrote:
> > > On Wed, Feb 19, 2020 at 11:08:39AM -0800, kan.liang@xxxxxxxxxxxxxxx wrote:
> > >
> > > SNIP
> > >
> > > > +static bool violate_nmi_constraint;
> > > > +
> > > > +static bool metricgroup__has_constraint(struct pmu_event *pe)
> > > > +{
> > > > +	if (!pe->metric_constraint)
> > > > +		return false;
> > > > +
> > > > +	if (!strcmp(pe->metric_constraint, "NO_NMI_WATCHDOG") &&
> > > > +	    sysctl__nmi_watchdog_enabled()) {
> > > > +		pr_warning("Splitting metric group %s into standalone metrics.\n",
> > > > +			   pe->metric_name);
> > > > +		violate_nmi_constraint = true;
> > >
> > > no static flags plz.. can't you just print that rest of the warning in here?
> >
> > Because we only want to print the NMI watchdog warning once.
> > If there are more than one metric groups with constraint, the warning may be
> > printed several times. For example,
> >    $ perf stat -M Page_Walks_Utilization,Page_Walks_Utilization
> >    Splitting metric group Page_Walks_Utilization into standalone metrics.
> >    Try disabling the NMI watchdog to comply NO_NMI_WATCHDOG metric
> > constraint:
> >        echo 0 > /proc/sys/kernel/nmi_watchdog
> >        perf stat ...
> >        echo 1 > /proc/sys/kernel/nmi_watchdog
> >    Splitting metric group Page_Walks_Utilization into standalone metrics.
> >    Try disabling the NMI watchdog to comply NO_NMI_WATCHDOG metric
> > constraint:
> >        echo 0 > /proc/sys/kernel/nmi_watchdog
> >        perf stat ...
> >        echo 1 > /proc/sys/kernel/nmi_watchdog
> > Is it OK?
> >
> > If it's OK, I think we can remove the flag.
>
> we use the 'print once' static flags in functions,
> so plz keep it inside like WARN_ONCE, or use it directly

If using WARN_ONCE, the warning is always printed for the first 
violation. For example,

 #perf stat -M Page_Walks_Utilization,Page_Walks_Utilization
 Splitting metric group Page_Walks_Utilization into standalone metrics.
 Try disabling the NMI watchdog to comply NO_NMI_WATCHDOG metric 
constraint:
     echo 0 > /proc/sys/kernel/nmi_watchdog
     perf stat ...
     echo 1 > /proc/sys/kernel/nmi_watchdog
 Splitting metric group Page_Walks_Utilization into standalone metrics.


The output of current patch is as below.
 #perf stat -M Page_Walks_Utilization,Page_Walks_Utilization
 Splitting metric group Page_Walks_Utilization into standalone metrics.
 Splitting metric group Page_Walks_Utilization into standalone metrics.
 Try disabling the NMI watchdog to comply NO_NMI_WATCHDOG metric 
constraint:
     echo 0 > /proc/sys/kernel/nmi_watchdog
     perf stat ...
     echo 1 > /proc/sys/kernel/nmi_watchdog


Personally, I think the output of current patch looks better.
But there is nothing wrong with the output of WARN_ONCE.

Should I use WARN_ONCE in next V2?

Thanks,
Kan