Re: Getting PEBS to work

[Arnaldo Carvalho de Melo <acme@kernel.org>]

Em Tue, May 24, 2016 at 12:17:26PM +0200, Peter Zijlstra escreveu:
> On Mon, May 23, 2016 at 11:05:39AM -0300, Arnaldo Carvalho de Melo wrote:
> > > # dmesg | egrep -i 'pmu|pmc|pebs'
> > > [    0.381095] Performance Events: PEBS fmt1+, 16-deep LBR,
> > > SandyBridge events, full-width counters, Intel PMU driver.
> > > [    0.381101] perf_event_intel: PEBS disabled due to CPU errata,
> > > please upgrade microcode
> > > [    0.395348] NMI watchdog: enabled on all CPUs, permanently consumes
> > > one hw-PMU counter.
> > > [    1.231836] nouveau  [     PMC][0000:01:00.0] MSI interrupts enabled
> > > 
> > > Gah, it was there all along!
> > 
> > Wish this was exported by the kernel somehow, then tooling could emit a
> > sensible message :-\
> 
> You mean something like so?

Probably, I'll try prototyping the tooling part later.

Thanks!

- Arnaldo
 
> --- a/arch/x86/events/core.c
> +++ b/arch/x86/events/core.c
> @@ -1716,6 +1716,8 @@ ssize_t x86_event_sysfs_show(char *page,
>  	return ret;
>  }
>  
> +static struct attribute *x86_pmu_attrs[];
> +
>  static int __init init_hw_perf_events(void)
>  {
>  	struct x86_pmu_quirk *quirk;
> @@ -1779,6 +1781,9 @@ static int __init init_hw_perf_events(vo
>  			x86_pmu_events_group.attrs = tmp;
>  	}
>  
> +	if (!x86_pmu.pebs)
> +		x86_pmu_attrs[1] = NULL;
> +
>  	pr_info("... version:                %d\n",     x86_pmu.version);
>  	pr_info("... bit width:              %d\n",     x86_pmu.cntval_bits);
>  	pr_info("... generic registers:      %d\n",     x86_pmu.num_counters);
> @@ -2120,10 +2125,20 @@ static ssize_t set_attr_rdpmc(struct dev
>  	return count;
>  }
>  
> +static ssize_t pebs_show(struct device *cdev,
> +			 struct device_attribute *attr,
> +			 char *buf)
> +{
> +	return snprintf(buf, 40, "%d\n",
> +			!!(x86_pmu.pebs_active && !x86_pmu.pebs_broken));
> +}
> +
>  static DEVICE_ATTR(rdpmc, S_IRUSR | S_IWUSR, get_attr_rdpmc, set_attr_rdpmc);
> +static DEVICE_ATTR_RO(pebs);
>  
>  static struct attribute *x86_pmu_attrs[] = {
>  	&dev_attr_rdpmc.attr,
> +	&dev_attr_pebs.attr,
>  	NULL,
>  };
>